The calculation of variable pressure flowmeters is reduced to determining the diameter of the hole and other sizes of the nozzle or diaphragm, the flow coefficient, the dynamic range of measurement, determined by the Reynolds numbers, the pressure drop and pressure loss on the orifice device, the expansion correction factor, as well as the measurement error of the gas flow rate. For the calculation, the maximum (limit), average and minimum flow rates, ranges of pressure and temperature changes of the gas, internal diameter and material of the measuring pipeline, gas composition or density under normal conditions, allowable pressure loss or limiting pressure drop corresponding to the maximum flow rate, as well as the average barometric pressure at the installation site of the differential pressure gauge-flowmeter.

Method of calculation. Before starting the calculation, we select the types and accuracy classes of the differential pressure gauge-flowmeter, pressure gauge and thermometer. The calculation is carried out as follows.

1. Determine the auxiliary coefficient rounded to three significant figures WITH when substituting into it the value of the maximum (limiting) flow Q n. etc, temperature and pressure, gas density under normal conditions ρ n, compressibility factor Z and measuring pipeline diameter D:

With the found value of C, two types of calculation are possible: according to a given pressure drop or according to given pressure losses. If the limit pressure drop Δ r pr, then according to the nomogram in Fig. 11 determine the preliminary relative narrowing m (modulus) of the narrowing device according to the found coefficient WITH and the specified limiting pressure drop across the constriction device Δ r pr, . Found preliminary modulo value m substitute in the formula by definition tα and calculate the preliminary flow rate α .

2. We calculate with an accuracy of four significant figures the auxiliary coefficient mα

Where ε - correction factor for gas expansion for the upper limit differential pressure of the differential pressure gauge Δ r pr , ; Δ r pr, - the upper limiting pressure drop on the narrowing device, kgf/m 2 .

3. Determine the refined value of the module m with an accuracy of four significant digits according to the formula

m = mα/α.

4. According to the refined value of the module m we find the new value of the correction factor for the extension e and calculate the difference between the originally calculated value ε and refined. If this difference does not exceed 0.0005, then the calculated values m And ε considered final.

5. Determine the diameter d diaphragm openings at the final selected m

6. Found values ​​of the flow coefficients α , correction factor for expansion ε , diameter d diaphragm openings, as well as Δ r pr, p 1, T 1, r n And Z use to determine the gas flow rate and check the calculation of the maximum gas flow rate Q n. etc. Received value Q n. etc. should not differ from the specified value by more than 0.2%. If the found value of the limiting gas flow rate differs from the specified value by more than 0.2%, then the calculation is repeated until the required error in calculating the limiting gas flow rate and the diaphragm parameters is obtained.

7. Define new refined module values m, diameter d orifice openings, as well as the flow coefficient α and recalculate. If the adjusted calculated value of the limiting gas flow rate does not differ from the specified value by more than 0.2%, then the adjusted values m, d And α , are fixed in the calculation sheet of the narrowing device.

8. Calculate the minimum and maximum Reynolds numbers and compare the minimum Reynolds number with the boundary values

9. Determine the thickness of the diaphragm E, the width of the cylindrical part of the diaphragm e c, the width of the annular gap With, as well as the dimensions of the annular chambers a And b.

10. We select the lengths of the straight sections of the measuring pipelines before and after the diaphragm.

11. Calculate the flow measurement error

The obtained data are recorded in the calculation sheet of the narrowing device and are the basis for its manufacture and installation.

Gas metering unit

Designed for commercial accounting of gas (measurement of its consumption). The number of measurement lines depends mainly on the number of outlet gas pipelines from the GDS. The technical implementation of gas flow measurement units must comply with the "Rules for measuring the flow of gases and liquids by standard restrictive devices" RD50-213-80.

Orifice area ratio F 0 to the cross-sectional area of ​​the gas pipeline F G is called the module T(or relative area): m = F 0 /F G.

On gas pipelines, a diaphragm with a diameter of at least 50 mm is used as a narrowing device, provided that its module has the following limits:

m \u003d 0.05-0.64 - for diaphragms with an angular method of sampling the pressure drop and gas pipelines with D y \u003d 500-1000 mm;

t = 0.04 - 0.56 - for diaphragms with a flanged pressure drop selection method and gas pipelines with D y \u003d 50 -760 mm.

Rice. 27 - Natural gas temperature-enthalpy curve

The smaller the module, the higher the accuracy of gas flow measurement, but the greater the pressure loss Δр in the diaphragm.

The aperture diameter of the diaphragm, regardless of the method of pressure drop, is assumed to be d ≥ 12.5 mm, and the ratio of the absolute pressure at the outlet of the diaphragm and at the inlet to it is ≥0.75.

In the gas pipeline near the diaphragm, the following conditions must be observed:

1) turbulent and stationary movement of the gas flow in straight sections must be ensured;

2) there should be no change in the phase state of the gas flow, for example, vapor condensation followed by condensate;

3) precipitation in the form of dust, sand, etc. should not accumulate inside the straight sections of the gas pipeline;

4) deposits (for example, crystalline hydrates) that change its design parameters should not form on the diaphragm.

However, on the inner wall of the gas pipeline, at the place of installation of the narrowing device, the deposition of solid crystalline hydrates is quite possible. And this leads to a significant error in the measurement of gas flow and a decrease in the throughput of the pipeline, as well as blockage of the impulse lines.

When designing a GDS gas metering unit operating in the hydrate formation mode, it is necessary to provide for measures that exclude hydrate formation. Their occurrence can be prevented by heating the gas, introducing inhibitors into the gas pipeline, and purging the narrowing device. An opening should be provided in the gas pipeline to remove precipitation or condensate. The diameter of such a hole should not exceed 0.08D 20, and the distance from it to the hole for measuring the pressure drop should not be less than D 20 or found from Table. 6. The axes of these holes should not be located in the same plane passing through the axis of the pipe.

There should be a straight section between the local resistance on the gas pipeline and the diaphragm, the length of which is the distance between the end surfaces of the diaphragm and local resistance (Fig. 28). The boundary of local resistances is considered:

1) for a bend - a section passing perpendicular to the axis of the gas pipeline through the center of the bend radius;

2) for weld-in constrictions and expansions - a welded seam;

3) for a tee at an acute angle or a branching flow - a section located at a distance of two diameters from the point of intersection of the axes of the pipelines;

4) for a welded group of elbows - a section located at a distance of one diameter from the weld closest to the elbow diaphragm.

Figure 28. Diaphragm installation diagram 1 - pressure gauge, 2 - thermometer, 3 - local resistance

In accordance with the requirements of Rules RD50-213-80, the measuring section of the gas pipeline must be straight and cylindrical, with a circular cross section. The actual inner diameter of the section in front of the diaphragm is determined as the arithmetic mean of the results of measurements in two cross sections directly at the diaphragm and at a distance from it 2D 20, moreover, in each of the sections in at least four diametrical directions The results of individual measurements should not differ from the average value by more than 0.3% ±2%.

Limit deviations for the inner diameter of pipes should not exceed the corresponding limit deviations for the outer diameter, i.e. ± 0.8%. It is allowed to mate the holes of the flange and the pipeline along a cone with a slope towards the diaphragm of not more than 1:10 and smooth rounding at the ends.

Sealing gaskets between the diaphragm and the flanges must not protrude into the internal cavity of the gas pipeline. When installing a diaphragm between the mounted flanges, the end of the gas pipeline must be directly adjacent to it.

The temperature behind the narrowing device is measured at a distance of at least 5 D20, but not more than 10 D20 from its rear end. The diameter of the thermometer sleeve should not exceed 0.13 D20. Immersion depth of thermometer sleeve (0.3 - 0.5) D20.

The inner edge of the hole for pressure tapping in the gas pipeline, in the flange and in the chamber should not have burrs, it is recommended to round it along the radius r = 0,ld of the hole. The angle between the axes of the hole and the chamber diaphragm is 90°.

Size d(single hole diameter) with module T< 0,45 не должен превышать 0,03D20, and with modulus m > 0.45 be within 0.01 D20d< 0.02D20.

If the distance between the knees exceeds 15 D20, then each knee is considered single; if it is less than 15 D20, then this group of knees is considered as a single resistance of this type. In this case, the inner radius of curvature of the elbows must be equal to the diameter of the pipeline or greater than it. The reduced length of the straight section in front of the diaphragm for any type of resistance, except for the thermometer sleeve, must be less than 10 D20.

General gas consumption

Where QM And Q V , - mass and volumetric flow rates of the gas flow; A - diaphragm flow coefficient; ξ- gas expansion coefficient; d- diaphragm opening diameter; ∆P- pressure drop across the diaphragm; ρ is the density of the gas.

In addition to diaphragms, restrictive devices complete with differential pressure gauges, as well as pressure gauges, are used to measure gas flow.

The device narrowing quick-change (USB). Together with a differential pressure gauge, this device (Fig. 29) makes it possible to measure the flow rate of gas transported through the GDS by measuring the pressure drop that occurs across the diaphragm and registering it with a differential pressure gauge.

Rice. 29 - Quick-change narrowing device USB 00.000.

1 - case: 2, 18 - loops; 3 - flange: 4, 16 - pads: 5. 9 - gaskets: b - cap nut: 7. 11 - rubber rings: 8 - studs: 10 - diaphragm: 12 - traffic jams: 13 - cuff: 14 - nozzle: /5 - handle: 17 - cover: /9 - plate.

The gas pressure is taken in front of the diaphragm from cavity B of the plus chamber, made in the chamber housing, and behind the diaphragm - from the cavity IN minus chamber in the flange (Fig. 29). Pressure is taken from these cavities through holes above the horizontal axis of the diaphragm (Fig. 29) A-A and static pressure - from the cavity B through a separate hole (Fig. 29) B-B.

Tightness between the plus and minus chambers is ensured by uniform pressing of the rubber ring to the flange plane with studs. The movement of gas through the gas pipeline causes additional pressing of the diaphragm by the velocity pressure. The diaphragm extraction window is sealed with a gasket. The gasket is preloaded with pins. With an increase in pressure in the pipeline, the gasket is additionally pressed against the surface of the positive chamber. In order to prevent the gasket from being bitten by the stud thread, a copper cuff is provided.

The joint between the flange and the body is sealed with an O-ring. Drainage lines are located at the bottom of the CSS. Impulse and drainage lines are muffled by process plugs. To facilitate the installation and dismantling of the lining with D y = 200 mm and above, two handles allow.

The pad is designed to increase the rigidity and centering of the lid, and the loop is used to set the lid in its working position.

Pressure gauges differential bellows self-recording (DSS). Used to measure gas flow at gas distribution stations by pressure drop in standard constriction devices.

The sensitive part of these differential pressure gauges is the bellows block, the principle of which is based on the relationship between the measured pressure drop and the elastic deformation of helical coil springs, bellows and torque tube. The scheme of the self-recording bellows differential pressure gauge and the device of the bellows block are shown in fig. thirty.

The bellows block has two cavities (+ and -) separated by a base 8 and two nodes of bellows 5 and //. Both bellows are rigidly connected to each other by a rod 12, the ledge of which rests the lever 7, fixed on the axis 2. The output of the axis from the working pressure cavity is carried out using a torsion tube /, the inner end of which is welded to the axis 2. a outer - with a torsion outlet base. stem end 12 connected with a block of range helical coil springs by means of a bushing 10. The movement of the rod by lever 7 is converted into a rotation of axis 2, which is perceived through the system of levers by the pointer of a self-recording or indicating instrument. The internal cavity of the bellows and the base to which they are attached is filled with a liquid consisting of 33% pure glycerol and 67% distilled water. The freezing point of this mixture is 17°C.

Both bellows have special valve devices that reliably keep fluid from flowing out of the bellows during one-sided overloads. The valve device consists of a cone on the bottom of the bellows and a sealing rubber ring 6. In case of one-way overload, the bellows conical valve with the O-ring sits on the base cone seat and blocks the passage of fluid from the bellows, protecting it from destruction.

To reduce the effect of temperature on instrument readings due to changes in the volume of liquid, the bellows 5 has a temperature compensator. Each nominal pressure drop corresponds to a certain range spring block 9.

Adjustment of bellows differential pressure gauges is carried out by changing the length of the adjustable leashes. Setting the flow rate arrow to zero is achieved by changing the angle of the lever 4. The zero position of the device corresponds to an angle of inclination equal to 28 ". The upper limit of measurement is regulated by changing the length of the rod 3.

Odorization block

For timely detection of gas leaks in gas pipeline connections, in stuffing boxes of shut-off and control valves, in connections of control and measuring equipment, etc., substances with a sharp unpleasant odor, called an odorant, must be added to natural gas. As such, ethyl mercaptan, pentalarm, captan, sulfan, etc. are used, most often ethyl mercaptan (its chemical formula C 2 H 5 SH), which is a colorless transparent liquid with the following basic physical and chemical properties:

The minimum amount of odorant in the gas must be such that the presence of gas is felt in the room at a concentration equal to 1/5 of the lower explosive limit, which corresponds to 16 g of odorant per 1000 m 3 of gas for natural gas.

Currently, synthetic ethyl mercaptan is used as an odorant, which has the same chemical formula C 2 H 5 SH and is in short supply. Instead, the SPM odorant developed by VNIIGAZ (TU 51-81-88) is used, which is a mixture of low-boiling mercaptans: 30% ethyl mercaptan and 50-60% iso- and n-propyl mercaptans and 10-20% isobutyl mercaptans. Industrial tests of the SPM odorant showed that its efficiency is higher than that of ethyl mercaptan at the same consumption rate: 16 g per 1000 m 3 of gas.

Abroad, mixtures of C 3 - C 4 mercaptans are widely used as odorants. They have been found to be chemically more stable than ethyl mercaptan.

It is usually higher in winter than in summer. In the initial period of operation of a newly constructed gas pipeline, the odorization rate is also insufficient.

For gas odorization, drip-type odorizers (manual), universal UOG-1 and automatic AOG-30 are used.

Drip type odorizing plant. It is universal, but it is mainly used at gas flow rates of more than 100,000 m3 / h. The odorizing plant consists of (Fig. 33) supply tank 5 with a supply of odorant, which is a cylindrical vessel with a level tube 13, which serves to determine the amount of odorant in the tank and its consumption per unit time: viewing window /6 and the corresponding piping with impulse tubes and valves; underground tank 7 for storing odorant and valves 8, 10 for connecting hoses when overflowing the odorant from the storage tank into the underground one.

Universal gas odorizer type UOG-1 (Fig. 34). When the main gas flow passes through the flow-measuring diaphragm, on which a pressure drop is created, under the influence of which, when the plus and minus cavities of the diaphragm are connected, a branched gas flow is formed. This stream flows through an injector dispenser, which is used as an ejector stream.

The latter, passing through the dispenser along the annular gap, creates a rarefaction in it, under the action of which it enters the gas pipeline with a branched flow through the filter and the float chamber from parallel tanks (consumable and measuring, having a level glass and a scale for controlling the flow of odorant per unit time) odorant

The float chamber is designed to eliminate the influence of the odorant level on dosing. To this end, the float chamber and the dispenser are positioned in such a way that the nozzle through which the odorant enters the dispenser coincides with the level of the odorant maintained in the float chamber by the float. When the chamber is filled with odorant, the float moves down and opens the valve. During normal operation of the dispenser, the float makes an oscillatory movement with an amplitude of 3-5 minutes and a frequency proportional to the flow rate of the odorant.

In order to reduce the consumption of odorant, the dispenser is equipped with a valve that shuts off the flow of odorant into the injector for a specified time. The valve is controlled by membranes. When pulsed pressure is applied to the cavity A(see fig. 35) the valve blocks the passage of the odorant; when pressure is released from the cavity A the membrane under the action of odorant pressure returns to its original position and the valve opens the passage to the odorant.

Cavity pressure gauge A The dispenser is served by a control system consisting of a time relay, an adjustable container and a valve.

Gas from the outlet gas pipeline enters the gas preparation unit to feed the odorizer pneumatic system. The preparation unit consists of a filter, a reducer and a pressure gauge. The gas in this unit is cleaned, the pressure is reduced to a supply pressure of 2 kgf/cm 2 .

The cycling of the command to the dispenser valve is controlled by moving the piston of the adjustable container; the ratio of the time of the entire cycle to the time of the open position of the valve - with a throttle using a stopwatch and a pressure gauge.

Below are the technical characteristics of the UOG-1 and AOG-30 odorizers

Technical characteristics of the universal odorizer UO G-1
Working pressure of gas, kgf/cm 2 ............ 2-12
Pressure drop across the diaphragm, kgf/cm 2 , at a maximum gas flow rate of 0.6
Odorant throughput, cm 3 /h.. 57-3150
Maximum gas consumption for feeding the installation, m 3 / h 1
Odorization accuracy, % ± 10
Ambient temperature. ° C. . . .	.... -40 to 50
Overall dimensions, mm: length.............	.... 465
width.................	.... 150
height.................	. . 800
Weight, kg.............	. . 63
Technical characteristics of automatic odorizing unit AOG-30
Working pressure of gas, kgf/cm 2 ............	2-12
Odorant throughput, cm/h....
The ratio of the highest flow rate of the odorized gas to the smallest .................... Nominal number of strokes of the pump plunger in 1 min. Odorization accuracy, %................	5:1 4 to 12 ±10
Maximum gas consumption for powering the installation, m 3 / h
Ambient temperature, °С........	-40 to 50

Odorization block. It consists of an odorant dispenser, a float chamber, a viewing window, an odorant filter, a valve, a ball valve, a filter, a reducer, pressure gauges, a time switch, an adjustable container and a valve.

Odorant dispenser(Fig. 35). It is an injector, where the odorant is fed through the nozzle 1, and the ejecting gas flow - through the annular gap

RU. Dosing chambers are sealed with rubber rings 3.

The operation of the dispenser with the control system for shutting off the odorant flow is carried out using valve 5 and a seat 4. Spring 8 ensures the tightness of the overlap of the valve 5 with the seat 4. The pressure in the cavity A the seat is closed under the action of the movement of the membrane 7. When pressure is released from the cavity A valve 5 returns to its original position. Membrane 6 moves under the pressure of the odorant.

The dispenser is equipped with a clutch 9, due to the rotation of which the gap changes T between nozzle 1 and mixer 10. Gap size T changes when calibrating the dispenser by capacity, after which the position of the coupling 9 is fixed with a lock nut 2.

float chamber(Fig. 36). It consists of a body with a cover, inside of which a hermetically sealed float is placed, attached to the stem with a cotter pin. The stem is equipped with a spool that sits on the saddle in the upper position. The sensor of the alarm system is installed in the cover on the bracket. In the slot of the sensor, a flag is moved, which, crossing the working area of ​​the sensor, causes it to operate.

viewing window(Fig. 37). Consists of body, sleeve and glass tube. The elements of the viewing window are sealed using rubber sealing rings.

Odorant filter(Fig. 38). Represents the cylindrical case with a cover in which the cartridge with a mesh bottom is screwed. The cassette is filled with a filter element - glass wool. The lid is sealed with an O-ring. The lower part of the body is used as a sump and has a sludge drain valve.

Rice. 39. Time relay.

/ - choke: 2 - intermediate ring: 3, 5 - membranes: 4 -

stem: b - cover: 7 - flange: 8 - screw: 9 - guides: 10 -

spring: 11 - valve: 12 - start button

Time relay(Fig. 39). The gas pressure is supplied to the cavity formed by the intermediate ring and two membranes, which are rigidly connected by screws through the flange and the ring with the stem. The rod has axial and radial holes. Under the action of the spring, the stem is in the upper position and rests against the flange.

Gas through the axial hole in the rod and the throttle enters the cavity formed by the cover and the membrane, on which it presses. The stem moves down and opens the relief valve. A button is provided to start the time relay.

Adjustable capacity(Fig. 40). Consists of body, covers, piston, screw and sealing tracks. Designed to regulate the supply of odorant to the gas pipeline.

Valve(Fig. 41). Its main elements are membranes, which have different affective areas and form two cavities: L and b, connected to each other by a valve through a control throttle. The flow area of ​​the throttle is regulated by a needle. The needle is moved by a screw with a flywheel. There is a scale on the face of the flywheel. The scale pointer is attached to the valve body with two screws.

Measuring capacity (Fig. 42). It is a cylindrical vessel with a level measuring glass tube equipped with a scale 2. The glass tube is protected by a casing and sealed with rubber rings.

Proportional gas odorizer OGP-02. Designed to automatically introduce an odorant (ethyl mercaptan) into a natural gas stream (in proportion to its flow rate) in order to give the gas a specific odor that will help detect leaks. The OGP-02 odorizer can be operated outdoors in a moderately cold climate at facilities with a conditional pressure of 16 kgf/cm2 and a gas flow rate of 1000 to 100,000 m3/h.

The odorizer consists (Fig. 43) of a dispenser and a control container. The dispenser contains a nozzle and an odorant level regulator. Inside the control tank there is a stainless steel float, a rod, on the upper part of which a magnet is fixed. A magnetic odorant level indicator slides along the outer surface of the tube.

The principle of operation of the OGP-02 odorizer is as follows (Fig. 43, 44). The odorant flows from the control tank through the valve until its level overlaps the lower edge of the level regulator. In the dispenser, with the help of a level regulator and technological piping of the containers, a constant, predetermined, level of odorant is maintained. Its supply to the gas pipeline is carried out due to the pressure drop on the flow-measuring diaphragm with the help of gas flow from the "plus" chamber through the impulse tube, nozzle, collector, through the tubes through the "minus" chamber into the gas pipeline. The gas flow from the nozzle, passing through the layer of odorant, takes out vapors and small droplets of it into the collector, and from it into the gas pipeline.

Replenishment of the dispenser with odorant is carried out from the supply and control containers with the valve open.

The adjustment of the odorizer to the required degree of gas odorization is carried out by changing both the thickness of the odorant layer above the upper end of the nozzle by the level controller and the gas flow through the nozzle by the valve.

The consumption of the odorant at any time for a certain interval (15-30 minutes) can be measured using a control container by closing the valve. The odorizer for the odorant consumption proportional to the gas consumption is adjusted twice: when switching from winter gas consumption to summer, and vice versa.

In the future, the consumption of the odorant, depending on the change in gas consumption, is automatically adjusted.

Maintenance of the OGP-02 odorizer is reduced to periodic filling of the working tank with odorant and subsequent start-up of the odorizer.

Rice. 44. Scheme of the gas odorizer OGP-02.

/ - dispenser: // - working (consumable) capacity. /// - control capacity. 1 - 10 - valves.

Switch block

Designed, firstly, to protect the consumer's gas pipeline system from possible high gas pressure; secondly, to supply gas to the consumer, bypassing the gas distribution station, through the bypass line using manual gas pressure control during repair and maintenance work of the station.

The switching unit consists of valves on the inlet and outlet gas pipelines, a bypass line and safety valves. As a rule, this unit should be located in a separate building or under a canopy that protects it from precipitation.

Safety valves. Two safety valves are mounted on the gas pipeline, one of which is working, the other is reserve. Valves of the CPPK type (special full-lift safety valve) (Fig. 45; Table 10) and PPK (spring full-lift safety valve) are used. A three-way valve of the KTPP type is placed between the safety valves, always open to one of the safety valves. Shut-off fittings must not be installed between the gas pipeline and the valves. The setting limits of the safety valves must exceed the rated gas pressure by 10%.

During operation, the valves should be tested for operation once a month, and in winter - once every 10 days with an entry in the operational log. Safety valves are checked and adjusted twice a year. about which they make an appropriate entry in the journal.

On the stem of the SPPK4R safety relief valve (Fig. 45), on the one hand, the gas pressure from the outlet gas pipeline acts, and on the other hand, the force of the compressed spring. If the gas pressure at the GDS outlet exceeds the set value, then the gas, overcoming the force of the compressed spring, raises the rod and connects the outlet gas pipeline to the atmosphere. After reducing the gas pressure in the outlet gas pipeline, the stem returns to its original position under the action of a spring, blocking the passage of gas through the valve nozzle, thus separating the outlet gas pipeline from the atmosphere. Depending on the setting pressure, safety valves are equipped with replaceable springs (Table 11). Table 11 - Choice of springs for safety valves type SPKK and PPK

Valve	Setting pressure, kgf/cm	Spring number	Valve	Setting pressure. kgf / cm 2	Spring number
SPPK4R-50-16	1.9-3.5		PPK4-50-16	1,9-3,5
	3.5-6.0			3,5-6,0
SPPK4R-80-16	2.5-4.5			6,0-10,0
	4.5-7,0			10,0- 16,0
SPPK4R-100-16	1 ,5-3,5		PPK4-80-16	2,5-4,5
	3,5-9,5			4,5-7,0
SPPK4R-150-16	1,5-2,0			7.0-9.5
	2,0-3,0			9.5-13.0
	3,0-6,5		PPK4-100-16	1.5-3.5
SPPK4R-200-16	0,5-8,0			3.5-9.5
				9.5-20
			PPK4-150-16	2.0-3.0
				3.0-6.5
				6.5-11.0
				11 - 15,0

Table 12 - Overall and connecting dimensions, mm, and weight of valves type PPK4

In addition to valves of the SPPK type, spring safety flange valves of the PPK-4 type (Fig. 46. Table 12) for a nominal pressure of 16 kgf / cm 2 are widely used. Valves of this type are equipped with a lever for forced opening and control purge of the gas pipeline. The spring is adjusted with an adjusting screw.

The gas pressure from the gas pipeline enters under the shut-off valve, which is held in the closed position by a spring through the stem. The tension of the spring is adjusted by a screw. The cam mechanism makes it possible to carry out control purge of the valve: by turning the lever, the force is transmitted to the stem through the shaft, cam and guide sleeve. It rises, opens the valve and purge occurs, which indicates that the valve is working and the discharge line is not clogged.

Valves PPK-4, depending on the number of the installed spring, can be adjusted to operate in the pressure range from 0.5 to 16 kgf/cm 2 (Table 13).

Capacity of safety valves G. kg/h:

G - 220Fp .

Where F- valve section, cm, determined for full-lift valves with h ≥ 0.25d by addiction F = 0.785d2; for partially lifted h≥ 0.05d - F= 2,22dh; d- inner diameter of the valve seat, cm; h- valve lift height, cm; R - absolute gas pressure, kgf/cm 2 ; T - absolute gas temperature, K; M - molecular weight of gas, kg.

To discharge gas into the atmosphere, it is necessary to use vertical pipes (columns, candles) with a height of at least 5 m from ground level; which lead out of the GDS fence at a distance of at least 10 m. Each safety valve must have a separate exhaust pipe. It is allowed to combine exhaust pipes into a common manifold from several safety valves with the same gas pressures. In this case, the common manifold is counted on the simultaneous discharge of gas through all safety valves.

Cranes. Cranes installed in switching blocks, as well as in other sections of GDS gas pipelines, differ in types of drives (Table 14).

1) crane type 11s20bk and 11s20bk1 - with a lever drive (Fig. 47, Table 15);

2) crane type 11s320bk and 11s320bk1 - with a worm drive (reducer) (Fig. 48; Table 16);

3) crane type 11s722bk and 11s722bk1 - with a pneumatic drive (Fig. 49; Table 17);

4) crane type 11s321bk1 - for a wellless installation (Fig. 50; Table 18);

5) crane type 11s723bk1 - for a wellless installation (Fig. 51 table I9)

Rice. 47. Cranes 1s20bk and 11s20bk1.

1 - body; 2 - cork; 3 - bottom cover: 4 - adjusting screw; 5 - spindle 6 - check valve for lubrication: 7 - grease bolt. 8 - lever: 9 - stuffing box.

Rice. 48. Cranes 11s320Bk and 11s320bk1.

1-body: 2-plug: 3 - bottom cover; 4 - adjusting screw: 5 - worm sector: b - worm. 7 - flywheel: 8 - grease bolt: 9 - check valve: 10 - gearbox housing: 11 - stuffing box. 12 - spindle: 13 - lid.

Rice. 49. Cranes 11s722bk (a) and 11s722bk1 (b) with D at 50 and 80 mm.

/ - body: 2 - stopper: 3 - heel; 4 - ball. 5 - set screw; 6 - coupling bolt: 7 - cap; 8 - bottom cover: 9 - gland packing: 10 - spindle: 11 - bracket: 12 - lever arm; 13 - in and lka: 14 - stock: 15 - pneum drive; 16 - multiplier: 17 - terminal switch; 18 - nipple. /- execution of flanged valves 1s722bks D at 50, 80, 100 mm.

Rice. 50 Crane 11s321bk1

All of the listed valves are made with ends both for flange connection (the designation ends with the letters "bk"), and for welding (the designation ends with the letters and the number "bk1"). The faucet body is made of steel, and the plug is made of cast iron. Cranes are mounted at an ambient temperature of -40 to 80 ° C.

On valves with a bypass, a through valve D y \u003d 150 mm is installed to facilitate the opening of the main valve by equalizing the pressure on both sides of the gate. The bypass valve is connected to the body of the main valve by bypass pipes.

The crane with a pneumatic drive consists of a crane assembly, a pneumatic drive and a multiplier. If necessary, the crane is controlled manually using a handwheel. The pneumatic actuator is pivotally connected to the valve body and provides reciprocating movement of the stem and rotation of the lever rigidly connected to the spindle with a key. The position of the rod is regulated by a fork pivotally connected to the lever.

A limit switch is installed on the cover of the gearbox, which cuts off the electric current in the control circuit at the end positions of the valve plug.

The multiplier is designed to supply special lubricant to the cavity under the top cover, as well as to the grooves of the body and plug. Lubrication seals and makes turning easier

traffic jams. To fill the multiplier with special grease, as it is consumed, a pneumatic grease blower is used.

The faucet assembly consists of the following main parts: body, plug, bottom cover and an adjusting screw that presses the plugs against the body seal. A lever (hand) operated faucet consists of a faucet assembly, gearbox or handle.

The main unit of the three-way valves used at the GDS is the shut-off valve, which consists of a body, a plug and a reducer.

6) Ball valves are also used on GDS (Fig. 52), the advantages of which over others are in simplicity of design, direct flow, low hydraulic resistance, and constant mutual contact of sealing surfaces. Distinctive features of ball valves from others:

1) the valve body and plug, due to their spherical shape, have

smaller overall dimensions and weight, as well as greater strength;

2) the design of valves with a spherical gate is less sensitive to manufacturing inaccuracies and provides much better tightness, since the contact surface of the sealing surfaces of the body and plug completely surrounds the passage and seals the valve gate;

3) the manufacture of these cranes is less laborious. In ball valves with plastic rings, there is no need to grind the sealing surfaces. Usually the cork is chrome plated or polished.

Ball valves are distinguished from others by a wide variety of designs. There are two main types of faucets: floating plug and floating ring.

Ball valves type KSh-10 and KSh-15 are designed to shut off pipelines, technological, control and safety equipment.

The tightness of the shut-off assembly (ball plug-seat) is ensured by tight coverage of a part of the spherical surface of the ball plug with a seat with some interference due to the ability of the seat material to deform when the valve parts are fastened with tie bolts. Materials for the manufacture of the saddle can be fluoroplastic, vinyl plastic, rubber or others with plastic deformation properties close to the properties of these materials. In case of wear of the sealing surfaces of the seat and loss of tightness by the shut-off assembly, the design of the valve provides for the possibility of restoring tightness by removing one or two gaskets installed on both sides between the body and the cover.

Aleksinsky plant "Tyazhpromarmatura" has mastered the serial production of ball valves with D y - 50, 80, 100. 150. 200. 700, 1000. 1400 mm per ru - 80 kgf / cm 2 of a modernized design with a plug in the supports and a seal made of elastomeric material (polyurethane or other materials with high wear resistance).

Valve bodies with D y - 50 - 200 mm are stamped, with a flange connector, and with D y \u003d 700. 1000. 1400 mm - all-welded, from stamped hemispheres (Fig. 53). The control units used in cranes (BUEP-5; EPUU-6) do not require additional piping in operating conditions, as they have a built-in terminal box and a limit switch. The cylinderless design of drives has significantly reduced the consumption of scarce hydraulic fluid for the hydraulic system of cranes. In addition, hand hydraulic pumps of a fundamentally new design are used in the cranes.

Rice. 52. Ball valve KSh without lubrication.

1- case: 2 - ball plug (rotary valve). 3 - saddle: 4 - spindle; 5 - cover (flanks): b - handle: 7 - sealing gasket: 8. 9 - sealing rubber rings: 10 - bolt: 11 - gasket

The plant manufactures the following ball valves:

МА39208 - D У 50, 80, 100, 150, 200 mm; RU 80 kgf / cm 2; with manual and pneumatic drive

MA39003 - D at 300 mm; p y 80 kgf / cm 2; with manual and pneumatic actuator MA39113 - D at 400 mm; p y 160 kgf / cm 2; with pneumohydraulic drive

MA39I12 - D at 1000 mm; p at 80 and 100 kgf / cm 2

MA39183 - D at 700 and 1400 mm: p at 80 kgf/cm2

MA39096 - DN 1200 mm; RU 80 kgf / cm 2

MA39095 - D at 1400 mm; r y 80 kgf / cm 2

MA39230 - D at 50. 80. 100. 150. 200 mm; p y 200 kgf / cm 2

Ball valves MA39208 with manual control D y - 50, 80, 100, 150 mm; r y 80 kgf / cm 2 are intended for use as a shut-off device on pipelines transporting natural gas (Table 20). There are a large number of original devices in the design of cranes. The valve assembly D y 50, 80. 100. 150 mm consists of two compact forged semi-bodies with one connector, the presence of one connector reduces the likelihood of depressurization of the valve assembly relative to the external environment. The central connector is sealed with a specially shaped rubber seal.

The design of the locking body is made according to the “plug in the supports” scheme, with self-lubricating plain bearings made of metal-fluoroplastic. The valve seal is made of polyurethane, which

Rice. 53. Ball valve with pneumohydraulic actuator.

1- crane body: 2 - gearbox manual: 3 - flywheel; 4 - column pipe. 5 - extension; 6 - Column: 7 - pipeline for supplying sealant to the seal: 8 - hydraulic drive: 9 - oil bottles

Table 20 - Overall, connecting dimensions, mm, and weight of ball valves

0,	p	ABOUT	D1	A		L	WITH	H	h,	Weight, kg
with pneumohydraulic drive	manually operated
	80- 160	190- 205					2155 (360)			580 (470)
							2215 (440)			820 (650)
	80- 125		386-398				2420 (625)	2815 (1020)	-	1475- 1480	-
							2530 (935)	3670 (2055)	3570 (1975)	4000 (3600)	3800 (3400)
							2610 (1015)	3970 (2375)	-	5560 (5110)	-
	80- 100		978- 988				2480 (1180)	4010 (2770)	-	10815 (10020)	-
									-		-
									-		-

Note. Dimensions and weights in brackets - for overhead cranes

pressed into a metal seat. Soft polyurethane seals of the gate are highly wear resistant, resistant to abrasive wear, erosion resistance and provide reliable sealing of the gate in all pressure ranges. Seats are pressed against the gate by the pressure of the transported medium and the force of the springs, which serve for reliable tightness of the gate at low pressures. Cranes are made with a manual drive, which is a lever. The technical characteristics of the crane are given below.

Proper use of the lens your camera is equipped with has a much greater impact on the sharpness of the resulting image than the choice of the lens itself. It makes no sense to look for the best lens. It just doesn't exist. One of the most important parameters when shooting is aperture. It is this that has the greatest impact on image quality. The difference between shots taken at different apertures with the same lens will be much more noticeable than the difference between shots taken at the same aperture but with different lenses.

F10 aperture, 1/400 shutter speed, ISO 64

F5 aperture, 1/400 shutter speed, ISO 64

What is aberration

As already mentioned, there is simply no perfect lens. The laws of physics have not been repealed and will never be repealed. And they do not allow the light beam to follow exactly the path that the opticians calculated for it within some ideal optical system. This is what leads to (spherical, chromatic, etc.). And the lens engineers can't fix it. In the center the lens is perfect. But closer to the edges, it distorts the light to some extent. The closer to the edge of the lens, the more the light is scattered and refracted.

When the aperture is fully open, the film or matrix of a digital apparatus receives light that is collected from the entire surface of the lens. In this case, all aberrations of the lens appear very clearly. When we cover the diaphragm opening, a part of the light flux passing through the edges of all lenses of the objective is cut off. Thus, only the center of the lens, which is free from distortion, takes part in the formation of the image.

Everything seems pretty simple. The smaller the aperture opening, the sharper the image. But it's not. When shooting at the smallest apertures, an unexpected big nuisance awaits us.

As the aperture aperture decreases, more of the light rays that pass through this aperture touch the edges of the aperture and deviate slightly from their main path. They seem to wrap around the edges. This phenomenon is called diffraction. During diffraction, each point of the object being photographed, even if it is clearly in focus, is projected onto the matrix not as a point, but as a small blurry spot, which is commonly called the Airy disk. And the size of this disk is the larger, the smaller the diaphragm opening. And when the diameter of the Airy disk exceeds the size of a single photodiode on the matrix, the blurring of the image becomes very noticeable. And the smaller we make the aperture, the more the diffraction increases.

The resolution of modern lenses is so high that even a slight blurring of the image caused by diffraction is already noticeable at aperture 11 and less. And compact cameras, which have very tiny sensors, do not allow, in principle, to use an aperture smaller than 8. At the same time, the small size of the matrix diodes makes diffraction very noticeable.

The focal length of the lens also matters. You need to remember what the f-number is. This is the ratio of the aperture diameter to the focal length of the lens. Simply put, at the same aperture value, the physical size of the hole in different lenses is very different. The physical size of the aperture is larger, the longer the focal length of the lens. Hence the conclusion: in lenses with different focal lengths at the same aperture value, diffraction manifests itself to different degrees. For example, at aperture 22 on a wide-angle lens, it is very noticeable, but on a lens focuser it is quite tolerable.

Sweet spot

The best aperture value for each lens individually. Usually it's 5.6 - 11 or so. It all depends on the lens model. Try opening the aperture wider - optical distortion will be more noticeable. And if you cover the aperture narrower - diffraction will begin to blur the image. At small apertures, for example, at 11 - 16, almost all lenses "draw" the same way. But at wide apertures, different lenses have very different image quality. The better the lens, the better the picture “drawn” by it with an open aperture.

Choosing the right aperture is a kind of balance between overall sharpness and depth of field. Here theoretical reasoning and recommendations are unlikely to help. In this case, you need to trust your experience, a clear understanding of the task, and, in the end, your artistic instinct, taste. But, nevertheless, some recommendations will not be superfluous.

How to choose the right aperture

• Determine the aperture at which your camera lens will produce the sharpest image, and always use that aperture whenever possible.
• If shooting takes place in low light, or you want to highlight something in the frame with a shallow depth of field, then the aperture can be increased. But without special need, do not open it completely.
• If such a need arose, the diaphragm must be boldly opened. Especially worry about this leash is not worth it. Aperture is not the most important thing that affects the sharpness of photos. Don't forget the "shake". It spoils the "picture" much more strongly than any aberrations.
• If, according to your plan in the picture, a large depth of field is required, the aperture must be covered. But no more than 11 for wide-angle lenses and 16 for telephoto lenses.
• If you still don’t have enough, then you can shoot with wide-angle lenses at 16 and long-focus lenses at 22. But no more. Otherwise, the overall sharpness of the image will noticeably drop.

Here, in fact, is the whole simple science. Now you, knowing about the weaknesses of your equipment, will be able to avoid those situations when they appear. And, therefore, it's time to squeeze all the juice out of your offspring.

Send your good work in the knowledge base is simple. Use the form below

Students, graduate students, young scientists who use the knowledge base in their studies and work will be very grateful to you.

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Course work

on the course "Technical measurements and devices"

"Calculation of standard narrowing devices"

• 1. Assignment for a course project
• 2. Calculation of the standard aperture
• 2.1 Theoretical part
• 2.2 Calculation procedure
• 2.3 Settlement part
• Conclusions on the course work
• Bibliography

1. Assignment for a course project

The calculation of the standard aperture is carried out according to the following data.

Medium: par.

Highest measurable mass flow.

Lowest measurable mass flow.

Absolute steam pressure in front of the CS.

Steam temperature in front of SS.

The greatest pressure difference on SU.

The inner diameter of the pipeline at a temperature of 20 o C .

The length of the straight sections of the pipeline before and after the SS.

The radius of the input edge of the SU.

Steel grade SU: 08X22H6T.

Pipeline steel grade: 20L.

Way of selection of pressure: flange.

Condition of the inner wall of the pipeline: new.

Permissible calculation error.

2. Calculation of the standard aperture

2.1 Theoretical part

Consumption is one of the most important technological parameters in thermal and nuclear power plants. Accurate flow measurement is necessary to ensure the required quality of process control, maintain reliable and trouble-free operation of equipment, and calculate the technical and economic performance of a power plant.

The method of measuring the flow rate by a variable pressure drop across a narrowing device (DR) is one of the most common and well-studied. The advantages of this method include the relative simplicity of design and compactness of primary flow converters.

Among constriction devices of various designs (diaphragms, nozzles, tubes and Venturi nozzles), diaphragms are most widely used. Their main advantages are the ease of manufacture and installation, as well as the possibility of using them to measure the flow rate of a substance in a wide range of flow rates in pipelines with a diameter of 0.05 to 1 m.

In this course project, the calculation of a standard diaphragm with a flanged method of pressure extraction through annular chambers was made.

nuclear power plant constricting diaphragm

Fig.1. Standard diaphragm.

1 - input end of the diaphragm; 2 - outlet end of the diaphragm.

2.2 Calculation procedure

1. According to the given parameters of the measured medium (temperature t and pressure p), the density, dynamic viscosity and adiabatic index k are found.

2. Based on the given temperature of the measured medium, the temperature coefficients of expansion of the material of the pipeline and the diaphragm are found according to the formula adj. 2:

,

,

Where

4. Determine the value of the equivalent surface roughness of the pipeline and the arithmetic mean deviation of the roughness profile according to the table app. 3 .

5. Calculate the upper and lower limits of the operating range of Reynolds number values:

;

,

6. Calculate the value of the auxiliary quantity A:

,

7. The values ​​of the lower and upper limits of the range of change relative to the diameter of the narrowing device are set.

8. Determine the values ​​of the expansion coefficients of the measured medium (at) and (at) by the expression:

,

9. Calculate the values ​​of the entry speed coefficients (at) and (at) according to the formula:

.

10. Calculate the values ​​of the expiration coefficients (at Re=Re max and) and (at Re=Re max and) according to the formula adj.4

Where, .

Values ​​and take

- for the angular method of pressure sampling;

, - for the three-radius method of pressure sampling.

11. Determine the values ​​of the roughness coefficients of the inner surface of the pipeline (at Re=Re max and) and (at Re=Re max and) according to the formulas of App.5

If the value of the standard deviation of the pipeline roughness profile satisfies the condition

, That.

Values ​​are calculated using the formula

The values ​​of the coefficients A 0 , A 1 and A 2 are determined by the formula

where are constant coefficients, the values ​​of which are given in

tab. P5.1.

If

, That.

The value is calculated by the formula

If or then.

If or, then the correction factor is calculated by the expression

The coefficients and are calculated by the formula

,

where, and - coefficients, the values ​​of which are given

in table. P 5.2.

12. Determine the values ​​of the diameter of the hole of the narrowing device (at) and (at according to the formula.

13. Determine the values ​​of the coefficients of blunting of the input edge of the tapering device (at and (at

If the radius of the leading edge, then the coefficient of blunting.

If the radius of the leading edge, then the value is calculated by the expression

.

14. Calculate the value of auxiliary quantities and by the expressions:

,

.

15. Consider the values ​​​​of auxiliary quantities and according to the formulas

,

.

If the values ​​and have the same sign, then the calculation is stopped, since in the range of acceptable values ​​there is no value that satisfies the initial data.

If the values ​​and have different signs, then the calculation is continued.

16. Calculate the value using the formula

.

17. Calculate the value of the auxiliary quantity B:

,

where the calculation of E is performed similarly to paragraph 9, - similarly to paragraph 13, C and in accordance with paragraphs 10 and 11 with, and the value in accordance with paragraph 8 with, and.

18. Check the fulfillment of the inequality.

If the above inequality is not satisfied, then repeat steps 16 - 18, replacing in the formula of paragraph 16 and with and (for B A).

If the above inequality is satisfied, then the found values ​​are considered final.

19. Check the condition

.

20. Determine the diameter of the hole under operating conditions d according to the expression from paragraph 12.

21. Calculate the diameter of the hole of the narrowing device when

temperature 20:

.

.

,

where is the maximum mass flow rate, kg/s; - allowable calculation error, %.

,

- yield strength of the diaphragm material under operating conditions, Pa

,

,

.

,

where, is the modulus of elasticity of the diaphragm material, Pa.

The values ​​and are found by .

.

27. The remaining aperture sizes are selected depending on the type by ,,,,.

2.3 Settlement part

1. According to the given parameters of the measured medium (temperature t and pressure p), we find the density, dynamic viscosity and adiabatic index k.

Po and Pa:

2. Based on the given temperature of the measured medium, we find the temperature coefficients of expansion of the material of the pipeline and the diaphragm according to the formula adj. 2:

,

where t is the temperature of the measured medium, o C; - constant coefficients, the values ​​of which are given in table. P2.1.

Because the temperature of the steam in front of the SU is 415 o C, and the temperature measurement limits of the SU 08X22N6T material are from -40 o C to 300 o C, then I choose another SU material - 08X18H10T.

Temperature expansion coefficients of pipeline material

Thermal expansion coefficients of diaphragm material

3. We calculate the value of the internal diameter of the pipeline under operating conditions:

,

where is the diameter of the pipeline at a temperature of 20 °C, m; t - temperature, °C.

m.

4. We determine the value of the equivalent surface roughness of the pipeline and the arithmetic mean deviation of the roughness profile according to the table adj. 3 .

5. Calculate the upper and lower limits of the operating range of Reynolds number values:

;

,

where and - respectively, the largest and smallest mass flow, kg / s.

6. Calculate the value of the auxiliary quantity A:

,

where is the maximum pressure drop across the constriction device, Pa.

7. We set the values ​​of the lower and upper limits of the range of change relative to the diameter of the narrowing device.

;

.

8. Determine the values ​​of the expansion coefficients of the measured medium (at) and (at) by the expression:

,

where is the absolute vapor pressure in front of the restrictor, Pa.

At:

.

At:

.

9. Calculate the values ​​of the entry speed coefficients (at) and (at) according to the formula

.

At:

.

At:

.

10. Calculate the values ​​of the coefficients of expiration (at and) and (at and) according to the formula adj.4

Where,

.

- for the flange method of pressure sampling;

At and:

,

,

.

At and:

,

,

.

11. We determine the values ​​of the roughness coefficients of the inner surface of the pipeline (at and) and (at and) according to the formulas of App.5

At and:

.

m.

The value is calculated by the formula

Since, then m.

Since then.

At and:

The value is calculated by the formula

The value is calculated by the formula

, because Re<3·10 6 , то

Since then

12. Determine the values ​​of the diameter of the hole of the narrowing device (at) and (at according to the formula

.

At:

m.

At:

m.

13. Determine the values ​​of the coefficients of blunting of the leading edge of the tapering device (at and (at

At:

Since then

.

At:

Since then

14. Calculate the value of auxiliary quantities and by expressions

15. We consider the values ​​of auxiliary quantities and according to the formulas

.

.

Since the quantities and have different signs, we continue the calculation.

16. Calculate the value using the formula

.

17. Calculate the value of the auxiliary quantity B:

Calculate the value of the entry speed coefficient

.

Calculate the value of the expiration coefficient

At and:

.

.

Determine the value of the roughness coefficient of the inner surface of the pipeline

At and:

The value is calculated by the formula

.

Because

>15 then.

The value is calculated by the formula

,

Because.

Since then.

Let us determine the value of the coefficient of blunting of the input edge of the tapering device

At m.

Since then

.

Let us determine the value of the expansion coefficient of the measured medium

At:

.

18. Checking the fulfillment of the inequality

,

.

Since the above inequality is not satisfied, we repeat steps 16–18, replacing in the formula of step 16 and with and (for B A). We summarize all subsequent iterations in a table.

	1 experience	2 experience	3 experience	4 experience	5 experience	6 experience	7 experience
	8 experience	9 experience	10 experience	11 experience	12 experience	13 experience	14 experience	15 experience

Since the above inequality holds (0.0000346<0.00005), то найденные значения считают окончательными.

19. Check the condition

.

Since for diaphragms with flanged pressure tapping

,

.

The condition is met.

20. We determine the diameter of the hole under working conditions d according to the expression from paragraph 12:

m.

21. Calculate the diameter of the hole of the narrowing device at a temperature of 20:

m.

22. Calculate the value of the mass flow rate corresponding to the largest pressure drop across the narrowing device:

.

23. Check the condition

,

,

.

The condition is met.

24. Choose the thickness of the diaphragm disk according to the formulas adj. 6

MPa, E y \u003d 1.623 10 11 Pa.

The maximum value of the disk thickness must satisfy the condition

,

where is the diameter of the pipeline opening under operating conditions, m.

m.

.

.

The values ​​of and are found by expressions

,

.

The values ​​of the coefficients and included in the formula are found by the expressions

.

The minimum disc thickness must meet the following conditions

;

,

where is the largest pressure drop across the narrowing device, Pa;

is the yield strength of the diaphragm material under operating conditions,

- relative aperture diameter.

Received mm.

25. Choose the length of the cylindrical part of the diaphragm hole e within

.

.

Received mm.

26. The angle of inclination of the generatrix of the cone to the axis of the aperture of the diaphragm is chosen within.

Accepted

27. The remaining aperture sizes are selected depending on the type.

For diaphragms with a flanged pressure tap, the location of the holes is shown in Figure b. Distance l 1 is measured from the inlet end of the diaphragm, and the distance l"2 - from the outlet end of the diaphragm.

Values l 1 and l" 2 can be within the following limits:

(25.4 ± 0.5) mm with v > 0.6 and D< 0,15 м;

(25.4 ± 1) mm in other cases.

l 1 = 26.4 mm, l" 2 \u003d 26.4 mm.

The center line of the hole must intersect with the center line of the IT at an angle of 90° ± 3°.

The edges of the hole at the point of exit to the IT should be flush with the internal surface of the IT and as sharp as possible. To eliminate burrs on the inner edge of the hole, it is allowed to blunt it with a radius of not more than one tenth of the hole diameter. No unevenness is allowed on the inner surface of the hole and on the IT itself near the hole.

The hole diameter must be no more than 0.13 D and no more than 13 mm. I took the diameters of the holes equal to 10 mm.

When choosing the diameter of the hole, it is necessary to exclude the possibility of clogging.

The orifice inlet face (see Figure 1) must be flat. The non-flatness of the surface of the inlet end of the diaphragm is determined before its installation.

The slope, characterized by the ratio N D / l D, must satisfy the condition:

If l = D, That

2H D /( D - d) < 0,005.

Table 1 (GOST 8.586.2-2005) shows the maximum allowable values ​​of H D depending on D and in at l = D.

At v=0.3405 and D=0.35213 m, N D max =0.58109 10 -3 m.

Let's take N D \u003d 0.55 10 -3 m, l D \u003d 0.116115 m.

Conclusions on the course work

In the course of the course work, a standard diaphragm with a flanged pressure tap was calculated.

The calculation of a standard orifice is based on solving the flow equation and consists in determining the relative diameter of the orifice in an iterative way.

At the first stage, the relative diameter was determined by an iterative method and the value of the mass flow rate kg/s was calculated.

At the second stage, the required dimensions were calculated for the manufacture of a standard diaphragm m, m, .

At the third stage, a drawing was made according to the found dimensions.

Bibliography

1. Kochetkov A.E., Malkova E.L. Calculation of the standard aperture: method. instructions / Ivan. state energy un-t. - Ivanovo, 2014.

2. GOST 8.586.2-2005 State system for ensuring the uniformity of measurements. Measurement of flow and quantity of liquids and gases using standard orifice devices. Part 2. Diaphragms. Technical requirements. - M.: Standartinform, 2006. - 43 p.

3. GOST 8.586.1-2005 State system for ensuring the uniformity of measurements. Measurement of flow and quantity of liquids and gases using standard orifice devices. Part 5. Measurement technique. - M.: Standartinform, 2006. - 87p.

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The aperture of a camera is one of three factors that affect exposure. Therefore, understanding the action of the aperture is a prerequisite in order to take deep and expressive, correctly exposed photographs. There are both positives and negatives to using different apertures, and this tutorial will teach you what they are and when to use which.

Step 1 - What is a camera aperture?

The best way to understand what a diaphragm is is to think of it as the pupil of the eye. The wider the pupil is open, the more light enters the retina.

Exposure consists of three parameters: aperture, shutter speed and ISO. The aperture diameter regulates the amount of light entering the matrix, depending on the situation. There are various creative uses for the aperture, but when it comes to light, it's important to remember that wider apertures let in more light and narrower apertures less.

Step 2 - How is aperture determined and changed?

Aperture is determined using the so-called aperture scale. On the display of your camera, you can see the F/number. The number means how wide the aperture is, which in turn determines the exposure and depth of field. The lower the number, the wider the hole. This can cause confusion at first - why does a small number correspond to a large aperture? The answer is simple and lies in the plane of mathematics, but first you must know what the f-series or standard f-stop scale is.

Diaphragm row:f/1.4f/2,f/2.8f/4,f/5.6f/8,f/11,f/16f/22

The main thing you need to know about these numbers is that there is one exposure step between these values, that is, when moving from a smaller value to a larger one, half the light will enter the lens. In modern cameras, there are also intermediate aperture values ​​that allow you to more accurately adjust the exposure. The tuning step in this case is ½ or 1/3 steps. For example, between f/2.8 and f/4 there will be f/3.2 and f/3.5.

Now for more complex things. More precisely, why the amount of light between the main aperture values ​​\u200b\u200bis two times different.

It comes from mathematical formulas. For example, we have a 50mm lens with an aperture of 2. To find the diameter of the aperture, we have to divide 50 by 2 to get 25mm. The radius will be 12.5 mm. The formula for the area is S=Pi x R 2 .

Here are some examples:

50mm lens with f/2 = 25mm. The radius is 12.5 mm. The area according to the formula is 490 mm 2. Now let's calculate for f / 2.8 aperture. The diaphragm diameter is 17.9 mm, the radius is 8.95 mm, the hole area is 251.6 mm 2 .

Dividing 490 by 251 is not exactly two, but that's only because f-numbers are rounded to the first decimal place. In fact, the equality will be exact.

This is how the ratios of the diaphragm openings really look.

Step 3 - How Does Aperture Affect Exposure?

As the aperture size changes, the exposure also changes. The wider the aperture, the more strongly the matrix is ​​exposed, the brighter the image is obtained. The best way to demonstrate this is to show a series of photographs where only the aperture changes and the rest of the parameters remain unchanged.

All images below were taken at ISO 200, shutter speed 1/400 sec, no flash, and only the aperture was changed. Aperture values: f/2, f/2.8, f/4, f/5.6, f/8, f/11, f/16, f/22.

However, the main property of the aperture is not exposure control, but a change in the depth of field.

Step 4 - Depth of field effect

Depth of field is a vast topic in itself. To open it, you need several dozen pages, but now we will consider it very briefly. We are talking about the distance that will be transmitted sharply in front and behind the subject.

All you really need to know, in terms of the relationship between aperture and depth of field, is that the wider the aperture (f/1.4) the shallower the depth of field, and the narrower the aperture (f/22) the greater the field of field. Before I show you a selection of photos taken with different apertures, take a look at the chart below. It helps to understand why this is happening. If you do not understand exactly how it works, it's okay, as long as it is important for you to know about the effect itself.

The image below shows a photo taken at f/1.4. It has a pronounced DOF effect (Depth of Field)

Finally, a selection of photos taken in aperture priority, so the exposure remains constant, and only the aperture changes. The aperture row is the same as in the previous slide show. Notice how the depth of field changes as you change the aperture.

Step 5 - How to use different apertures?

First of all, remember that there are no rules in photography, there are guidelines, including when it comes to choosing an aperture. It all depends on whether you want to apply an artistic technique or capture the scene as accurately as possible. To make it easier to make a decision, here are some of the most traditionally used aperture values.

f/1.4: Excellent for shooting in low light, but be careful, this setting has very little depth of field. Best used for small objects or to create a soft focus effect.

f/2: The use is the same, but a lens with this aperture may cost one third of a lens with aperture 1.4

f/2.8: Also good for low light conditions. It is best used for portraits, as the depth of field is greater and the entire face will be included, not just the eyes. Good zoom lenses usually have this aperture value.

f/4: This is the minimum aperture used to take a picture of a person in sufficient light. Aperture can limit autofocus performance, so you risk missing wide open.

f/5.6: Good for 2 person photography, but for low light it is better to use flash light.

f/8: Used for large groups as it guarantees sufficient depth of field.

f/11: At this setting, most lenses are at their sharpest, so it's good for portraits.

f/16: Good value when shooting in bright sunlight. Great depth of field.

f/22: Suitable for shooting landscapes where attention to detail in the foreground is not required.

The most fully studied constriction devices, which are recommended for widespread use by Technical Committee 30 (TC 30) of the International Organization for Standardization (ISO), are the so-called normal diaphragm and normal nozzle [?]. Based on periodically issued ISO recommendations, almost all industrialized countries have developed standards or regulations for the use of these restrictive devices.

In our country, similar standards for the methodology and formulas for calculating standard narrowing devices, the basic requirements for flow meters, the methodology for their verification, as well as the methodology for determining the error in measuring flow are established by Rules 28-64 of the State Committee for Standards, Measures and Measuring Instruments under the Council of Ministers of the USSR. The rules apply to flow measurements of single-phase liquids and gases, as well as superheated vapors using standard restrictors installed inside a pipeline with a diameter of at least 50 mm, provided that the flow is steady, Reynolds numbers exceed certain values ​​and the pressure ratio before and after the restrictor does not reach a critical value.

Normal or standard diaphragm and nozzle are not chosen and recommended for use by chance. Their discharge coefficients in a wide range of Reynolds numbers almost do not change. An appreciable change occurs only at comparatively small Re. Therefore, at small R, standard diaphragms and nozzles are not used.

The standard diaphragm is a constriction device made in the form of a flat disk with a concentric hole for the fluid to flow out. A schematic representation of the diaphragm is shown in Fig. 3.

Above the axis, the measurement of the differential pressure through the annular chambers is shown, below the axis - through the individual holes. The following designations are adopted in the figure: D 20 - the inner diameter of the pipeline in front of the narrowing device at a temperature of 20 ° C; d 20 - the inner diameter of the diaphragm at the same temperature.

Rice. 3

The thickness of the disc should be in the range from 0.005D to 0.05D, where D is the diameter of the pipeline. If the disc thickness is more than 0.02D, then the hole on the exit side must have a conical bore with an angle ranging from 45 to 60° (previously from 30 to 45°). Thus, the thickness of the cylindrical hole of the diaphragm should be in the range from 0.005D to 0.02D. The entrance angle of the cylindrical hole should be strictly equal to 90 °, and the entrance edge itself should be sharp, without any burrs and notches. The degree of roughness k of the inlet end of the diaphragm is allowed by the Rules up to 0.005D, but it is stipulated that the wave (characterizing non-flatness) must exceed the height k by at least 200 times.

Rules 28-64 provide for only the angular method of taking pressures. In this case, two of its varieties are possible - point and chamber. In the first case, the selection is carried out by separate drillings, in the second, through the annular chambers, which are connected to the internal space of the pipeline using annular slots located directly at the diaphragm planes, or a group of holes evenly distributed around the circumference.

It is the latter method adopted in GOST 14321–73. Chamber diaphragms for R y up to 100 kgf / cm 2 (10 Pa). Annular chambers contribute to the selection of the average pressure in this section [?]. therefore, they are particularly useful when there is no certainty about the proper axial symmetry of the velocity profile, i.e. when there is insufficient length of straight pipe sections before and after the orifice.

Chamber diaphragms according to GOST 14321–73 are manufactured only with pipe diameters D no more than 400–500 mm. With large diameters, chamber pressure sampling is performed using two outer tubes of small (10–12 mm) diameter, bent into a ring around the main pipeline and connected to the space before and after the diaphragm using several (4–8) evenly spaced radial tubes.

The weak point of the diaphragm is the inlet edge, which becomes blunted under the action of the current flow, which leads to a gradual increase in its flow coefficient and the appearance of a negative sign error. In this regard, it is necessary to periodically monitor the condition of the diaphragm by removing it and inspecting it. To do this, it is necessary to turn off the section of the pipeline on which the diaphragm is installed. If an uninterrupted supply of the measured medium is required, then the diaphragm must be installed on a bypass line, equipped with locking devices to enable it to be turned off. The length of this line should be such that there are straight sections of sufficient length before and after the diaphragm. This greatly complicates the installation. In addition, the extraction process itself is laborious and is accompanied by damage to gaskets, and sometimes flanged pipes.

In this regard, in American practice, special devices have been widely used that allow you to remove diaphragms for revision and replacement without turning off the pipeline [?]. for this purpose, the disc diaphragm is placed in a special chamber, equipped with two flanges for installation in the pipeline. The chamber has two cavities separated by a locking element: in the lower one there is a diaphragm, the upper one acts as a gateway.

Diaphragms with one pair of differential pressure take-offs must be equipped with shut-off valves and nipples, as well as welded impulse pipes for connections 1-4; leveling condensation vessels according to GOST 14318-73 for connections 5-9; for connections 10-13 - impulse tubes and equalizing vessels in accordance with GOST 14319-73 or impulse tubes and separation vessels in accordance with GOST 14320-73. Diaphragms with several pairs of extractions are supplied with leveling condensate vessels, version 5 according to GOST 14319-73 without impulse tubes. The number of pairs of vessels must correspond to the number of differential pressure gauges supplied with the diaphragm. The designation of the chamber diaphragm indicates the conditional pressure, the conditional passage of the pipeline, the design of the seats, the material of the chamber and disk bodies, the connection number with impulse tubes or vessels and GOST.

Standard nozzles. Nozzles are especially convenient when measuring the flow of gases and superheated steam, as well as when measuring the flow of high pressure steam in pipelines with a diameter of D200mm. Compared to diaphragms, they are less sensitive to corrosion, contamination and provide somewhat greater measurement accuracy.

The standard Venturi nozzle consists of a shaped inlet, a cylindrical middle section and an outlet cone. The pressure loss in the Venturi nozzle increases with increasing cosine angle and decreasing cosine length. The Venturi nozzle is used where pressure loss is critical.