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1. The basic parameters of the valve are: nominal pressure PN, nominal diameter DN
2, the basic function of the valve: cut off the medium, adjust the flow, change the flow direction
3, the main way of valve connection: flange, thread, welding, clip
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4, the pressure of the valve - temperature grade means: different materials, different working temperatures, the maximum allowable non-impact working pressure is different
5. There are two main systems for pipe flange standards: the European system and the US system.
The pipe flange connections of the two systems are completely different in size and cannot be matched;
It is most appropriate to distinguish by pressure level:
The European system is PN0.25, 0.6, 1.0, 1.6, 2.5, 4.0, 6.3, 10.0, 16.0, 25.0, 32.0, 40.0 MPa;
The US system is PN1.0 (CIass75), 2.0 (CIass150), 5.0 (CIass300), 11.0 (CIass600), 15.0 (CIass900), 26.0 (CIass1500), 42.0 (CIass2500) MPa.
The types of pipe flanges are: integral (IF), plate flat welding (PL), neck flat welding (SO), neck butt welding (WN), socket welding (SW), screw (Th), butt weld ring Loose sleeve (PJ/SE) / (LF / SE), flat welding ring loose (PJ / RJ) and flange cover (BL).
The flange sealing surface types mainly include: full plane (FF), convex surface (RF), concave (FM) convex (M) surface, 榫 (T) groove (G) surface, ring connection surface (RJ), and the like.
Common (universal) valve
1. Valve type code Z, J, L, Q, D, G, X, H, A, Y, S respectively: gate valve, globe valve, throttle valve, ball valve, butterfly valve, diaphragm valve, plug valve, stop Return valve, safety valve, pressure reducing valve, steam trap
2, the valve connection code 1, 2, 4, 6, 7 respectively: 1 - internal thread, 2 - external thread, 4 - flange, 6 - welding, 7 - clip
3, the transmission mode of the valve code 9, 6, 3 respectively: 9 - electric, 6 - pneumatic, 3 - worm
4, valve body material code Z, K, Q, T, C, P, R, V respectively: gray cast iron, malleable cast iron, ductile iron, copper and alloy, carbon steel, chrome-nickel stainless steel, chrome-nickel-molybdenum stainless steel, Chrome molybdenum vanadium steel
5. Seat seal or lining code R, T, X, S, N, F, H, Y, J, M, W respectively: austenitic stainless steel, copper alloy, rubber, plastic, nylon plastic, fluoroplastic, Cr-based stainless steel, hard alloy, rubber, Monel, valve body material
6. Where the cast iron valve body is not suitable for use:
1) water vapor or wet gas with a large water content;
2) Flammable and explosive fluids;
3) When the ambient temperature is lower than -20 °C;
4) Compressed gas
Control valve
1. The control valve consists of a valve body and an actuator and its accessories.
2. The pneumatic diaphragm actuator has two forms: positive action and reverse action; as the signal pressure increases, the push rod moves down to a positive effect, whereas the push rod moves up to a reaction; usually accepts a standard signal pressure of 20~100KPa; with a positioner The maximum pressure is 250KPa. There are six basic strokes (mm): 10; 16; 25; 40; 60;
3. What are the characteristics of electric actuators compared with pneumatic actuators, and what are the output forms?
The driving source is simple and convenient for electric power, with large thrust and torque, and high rigidity. However, the structure is complicated and the reliability is poor. It is more expensive than pneumatics in small and medium sizes. It is often used in applications where there is no gas source or no strict explosion-proof or flameproof.
There are three output forms: angular stroke, straight stroke, and multi-turn.
4. What are the characteristics of the straight-through single-seat control valve? Where is the application?
1) The discharge flow is small, because only one spool is easy to seal. The standard discharge flow is 0.01% KV and is further designed as a shut-off valve.
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2) The allowable pressure difference is small, because the unbalanced force is large. The valve ΔP of DN100 is only 120KPa.
3) Small circulation capacity. The KV of the DN100 is only 120. It should be applied to occasions where the leakage is small and the pressure difference is not large.
5. What are the characteristics of the straight-through two-seat control valve? Where is the application?
1) The allowable pressure difference is large because it can offset many imbalance forces. The valve ΔP of DN100 is 280 KPa.
2) Large circulation capacity. The KV of the DN100 is 160.
3) The amount of leakage is large because two spools cannot be sealed at the same time. The standard discharge is 0.1% KV, which is a multiple of 10 for a single seat valve.
Mainly used in high pressure difference, where the leakage requirements are not strict.
6. What are the main advantages of the sleeve control valve?
It has the advantages of single and double seat valves. There are:
1) Good stability. The valve plug throttling is replaced by a valve plug throttling, and the valve plug is provided with a balance hole to reduce the imbalance force of the medium acting on the valve plug. At the same time, the guiding surface between the sleeve and the valve plug is large, and the unbalanced force changes little, so it is not easy to cause the valve core to vibrate.
2) Interchangeability and versatility. Different flow coefficients and different flow characteristics can be obtained by replacing the sleeve.
3) The pressure difference is allowed to be large, and the thermal expansion effect is small. The balance principle of the sleeve valve with the balance hole is the same as that of the double seat valve, so the allowable pressure difference is large. Since the sleeve and the valve plug are made of the same material, the expansion caused by the temperature change is basically the same.
4) The throttle window provided by the sleeve has two kinds of opening and small holes (jet type). The latter has the function of noise reduction and vibration reduction, and further improves the special low noise valve.
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It is suitable for occasions where the pressure difference between the valve and the valve is large and the noise requirement is low.
7. What other valves with adjustment function besides single, double seat and sleeve valves?
Diaphragm valve, butterfly valve, O-type ball valve (mainly cut), V-type ball valve (large adjustment ratio, with shearing action), eccentric rotary valve.
8. What is the adjustable ratio R of the regulating valve, the ideal adjustable ratio, and the actual adjustable ratio?
The ratio of the maximum flow to the minimum flow that can be controlled by the regulating valve is called the adjustable ratio R.
When the pressure difference across the valve remains constant, the ratio of the maximum flow to the minimum flow is called the ideal adjustable ratio.
In actual use, the pressure difference between the two ends of the valve changes, and the adjustable ratio at this time is called the actual adjustable ratio.
9. What is the flow coefficient C, Cv, KV of the regulating valve?
The flow capacity of the regulating valve is expressed by the flow coefficient.
1) Engineering unit system Cv definition: When the regulating valve is fully open, the differential pressure before and after the valve is 1kgf/cm2, and the number of cubic meters of water passing through the temperature of 5~40°C per hour.
2) Inch unit system C definition: When the regulating valve is fully open, the pressure difference between the valve and the front is 1bf/in2 (1 degree 60. F. The water per minute passed by the F.
3) International system of units KV: When the regulating valve is fully open, the differential pressure before and after the valve is 100 kPa, and the number of cubic meters of water passing through the temperature of 5 to 40 ° C per hour.
Cv=1.17 KV
KV=1.01 C
10. What is the force required by the actuator to meet the required force of the regulating valve?
1) Overcome the static imbalance caused by the spool.
2) Provide the tight pressure of the seat load.
3) Overcome the friction of the packing.
4) Additional forces (eg bellows, soft seals, etc.) required for a particular application or structure.
11. What is the flow opening and closing of the regulating valve?
It is related to the flow direction of the medium, and it is independent of the air opening and air closing of the regulating valve. The importance of flow is that it affects stability, leakage and noise.
Definition: At the orifice, the flow direction of the medium is the same as the opening direction of the valve.
12. Which valves need to be selected for flow direction? how to choose?
Single-sealed regulator valves such as single-seat valves, high-pressure valves, and single-sealed sleeve valves without balance holes require flow direction selection.
There are advantages and disadvantages to opening and closing. The flow-opening valve works stably, but the self-cleaning performance and the sealing performance are poor, and the service life is short; the flow-closed valve has a long service life, self-cleaning performance and good sealing performance, but the stability is poor when the valve stem diameter is smaller than the spool diameter. .
Single-seat valves, small-flow valves, and single-seal sleeve valves are usually selected for flow-opening. When flushing is strong or self-cleaning is required, flow closure is optional. The two-position quick-opening characteristic regulating valve is selected for flow closing type.
13. What are the three main factors that should be considered when choosing an implementing agency?
1) The output of the actuator is greater than the load of the regulator and is reasonably matched.
2) When checking the standard combination, the allowable pressure difference specified by the regulating valve meets the process requirements. When the pressure difference is large, the imbalance force of the spool is calculated.
3) Whether the response speed of the actuator meets the requirements of the process operation, especially the electric actuator.
14. What are the seven steps to determine the valve diameter?
1) Determine the calculated flow rate - Qmax, Qmin
2) Determine the calculated pressure difference - select the resistance ratio S value according to the characteristics of the system, and then determine the pressure difference when calculating (the valve is fully open);
3) Calculate the flow coefficient - select the appropriate calculation formula chart or software to find the max and min of KV;
4) KV value selection - according to the KV max value in the selected product series closest to the first gear KV, get the primary diameter;
5) Checking the opening degree - 90% valve opening is required when Qmax is required; 10% valve opening is required when Qmin is used;
6) Actual adjustable ratio check - general requirements should be ; 10; R actual > R requirements
7) Determine the caliber - if it is not qualified, re-select the KV value and verify.
15. What are the auxiliary devices (accessories) for pneumatic control valves? What role does each play?
1) Valve positioner - used to improve the working characteristics of the regulating valve to achieve correct positioning;
2) Valve position (stroke) switch - displays the stroke working position of the upper and lower limits of the regulating valve;
3) Pneumatic retaining valve - keep the position of the valve at the time of gas source failure;
4) Solenoid valve - automatic switching of the gas path. Single gas control with two three,; dual gas control with two five-way;
5) Manual mechanism - manual operation can be switched when the system is faulty;
6) Pneumatic relays - speed up the action of the pneumatic diaphragm actuator and reduce the transmission time;
7) Air filter pressure reducer - air source purification, pressure regulation;
8) Gas storage tank - When the gas source is faulty, the valve can continue to work for a period of time, generally requiring three sections of protection.
16. Under what circumstances do you need to use a valve positioner?
1) Where the friction is large and precise positioning is required. For example, high temperature, low temperature regulating valves or regulating valves using flexible graphite packing;
2) The slow process needs to increase the response speed of the regulating valve. For example, adjustment systems for parameters such as temperature, liquid level, and analysis.
3) It is necessary to increase the output force and cutting force of the actuator. For example, a single seat valve with DN ≥ 25 and a double seat valve with DN > 100. When the pressure drop across the valve is ΔP>1MPa or the inlet pressure P1>10MPa.
4) When the split-range adjustment system and the regulating valve are operated, it is sometimes necessary to change the air opening and air-closing forms.
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5) It is necessary to change the flow characteristics of the regulating valve.
17. What are the characteristics of the self-regulating valve? What do K and B in the self-operated pressure regulating valve model mean?
Self-operated regulating valve is also called direct acting regulating valve. There is no need for any additional energy, and the three functions of measurement, adjustment and execution are unified into one, and the regulating valve that uses the energy of the object itself to drive its action is utilized. It has the characteristics of simple structure, low price and reliable operation.
It is suitable for occasions where the flow change is small, the adjustment accuracy is not high, or the instrument air supply is difficult.
Self-operated regulating valves can be divided into pressure, liquid level, temperature and flow regulating valves according to their applications. Currently the most produced are pressure regulating valves and nitrogen sealing valves.
K——pressure type, pressure relief, stable before valve;
B——Compressed type, used for voltage regulation, stable after valve.