Valve selection basis
There are many articles on the selection of regulating valves. If the benevolent sees the wise and sees the wisdom, in this article, the valve engineers of Shenzhen Ming Valve confirm the control valve from the three aspects of the actuator, the valve body material, and the attachment according to the knowledge and industry experience. Selection:
First, the choice of executing agency
The actuators of the regulating valve can be divided into electric actuators, pneumatic actuators, and self-acting actuators.
1. The main advantage of the electric actuator is that the drive source (power supply) is convenient, but the price is high, and the reliability, waterproof and explosion-proof are not as good as the pneumatic actuators. The self-actuated actuator is cheap and easy to use, no gas source or power supply is required, but the adjustment performance is relatively Poor electric and pneumatic, the error will be a little larger, and it is not suitable for the occasion of normal temperature and high pressure
2. The commonly used foreign faults are opened or closed to indicate that the fault is open and the fault is closed. This is in contrast to the air-opening and air-closing indications in China. The fault opens the corresponding air-closed valve and the fault shuts off the corresponding air-opening valve. Choose according to need
3, some need to add hand wheel switch, in the case of failure of the actuator, manual operation
4, can choose according to the following
1) Reliability
Pneumatic actuators are simple and reliable: The poor reliability of old electric actuators is its past weaknesses. However, in the 1990s, the development of electronic actuators completely solved this problem. It can be repaired in 5 to 10 years, and its reliability is even greater. Exceeded pneumatic actuators. Therefore, the Shenzhen valve engineers believe that the electric control valve will become the mainstream of the next century regulating valve.
2) Drive source
The biggest deficiency of pneumatic actuators is the need to set up additional air source stations and increase the cost; the drive source for the electric control valve is desirable anywhere.
3) Price
Pneumatic actuators must be equipped with a valve positioner, plus a gas source. The cost is comparable to that of an electric control valve (imported electric valve positioner is equivalent to imported electronic actuators;
4) Thrust and stiffness
Both are equivalent.
5) Fire and explosion protection
The "pneumatic actuator + electric valve positioner" is slightly better than the electric actuator.
2.3 Recommendations
(1) When possible, it is recommended to use imported electronic actuators with domestic control valves (such as full-function ultra-light control valves) for localization and new projects.
(2) Although the film actuator has a lack of thrust, small rigidity, and large size, it has a simple structure. Therefore, it is still the most used actuator. But here we emphasize that it is best to use ZNA, ZHB fine small-film actuators instead of ZMA, ZMB type of old film actuators to get lighter weight, smaller size and large output force.
Second, the choice of valve body material
(1) The valve body pressure rating, service temperature and corrosion resistance should not be lower than the requirements of the process connection pipe
(2) Cast iron valves should not be used for water vapor or more wet gases and flammable and explosive media.
(3) When the ambient temperature is lower than -20°C (especially in the north), cast iron valves should not be used.
(4) In rectangular coordinates formed by medium temperature and pressure difference of cavitation and erosion, where the temperature is 300°C and the differential pressure is 1.5 MPa outside the area where the two points are connected, the throttle sealing surface shall be Wear resistant materials such as cobalt-based alloys or surfacing alloys.
(5) For highly corrosive media, corrosion resistant alloys must be selected based on the type, concentration, temperature, and pressure of the media.
(6) The valve body and the throttling element are treated separately. The throttling speed of the valve body wall is small and allows a certain degree of corrosion. The corrosion rate can be around lmm/year; the throttling piece is subject to high-speed erosion and corrosion will increase Large, the corrosion rate should be less than 0.1mm/year.
(7) When selecting the lining material (rubber, plastic), the temperature, pressure and concentration of the working medium must meet the scope of use of the material, and consider the physical and mechanical damage (such as shear failure) when the valve moves. .
(8) Vacuum valve should not use valve body lining rubber and plastic structure.
(9) The two shut-off valves of the water treatment system should not use lining rubber material.
(10) Typical corrosion resistant alloy material selection for typical media:
a. Sulfuric acid: 316L, Hastelloy, Alloy No. 20.
b. Nitric acid: Aluminum, C4 steel, C6 steel.
c. Hydrochloric acid: Hastelloy B.
d. Hydrofluoric acid: Monel.
e. Acetic acid, formic acid: 316L, Hastelloy.
f. Phosphoric acid: due to nickel, Hastelloy.
g. Urea: 316L.
h. Caustic soda: Monel.
i. Chlorine: Hastelloy C.
j. Seawater: Inconel, 316L.
(11) So far, the most versatile corrosion resistant material is tetrafluoride, known as "Corrosion Resistant King." Therefore, the PTFE corrosion resistant valve should be used first. In the last resort (eg, temperature>180°C, PN>1.6), the alloy is selected.
Third, the choice of flow characteristics:
(1) Logarithmic characteristics are selected when S>0.6.
(2) Logarithmic characteristics are selected when the small opening degree work and the imbalance force change greatly.
(3) The required adjusted parameters reflect the straight line when the speed is fast, and the logarithm when it is slow.
(4) Optional linear characteristics of the pressure regulation system.
(5) Optional linear characteristics of the liquid level adjustment system.
Fourth, the choice of attachments:
(1) The accessories for adjusting the control valve include: positioner, converter, relay, booster valve, retention valve, pressure reducing valve, filter, oil mister, travel switch, position transmitter, Solenoid Valve Handwheel mechanism.
(2) The attachment functions as a supplement and assures valve operation. Necessary increases, unnecessary increase. Adding attachments when they are not necessary increases prices and reduces reliability.
(3) The main function of the positioner is to increase the output force and the operation speed. When these functions are not required, it is not necessary to carry the positioner.
(4) For fast response system, do not valve fast, optional converter.
(5) Strict explosion-proof occasions, optional: electrical converter + pneumatic positioner.
(6) The solenoid valve should be chosen to be a reliable product that prevents it from moving when it is actuated.
(7) It is recommended that hand-wheels are not used in important situations to prevent human error.
(8) Preferably supplied by the manufacturer and supplied on the valve to ensure the reliability of the system and the assembly.
(9) When ordering, the name, type, specification, input signal, output signal, etc. of the accessories should be provided.
(10) Reiterate: Please note the importance of these "little things", especially the reliability. If necessary, you can use pneumatic components such as solenoid valves.
Shenzhen Ming Valve Import & Export Trading Co., Ltd., is the United States Weidun VTON valve, Germany Lutet LIT Valve Co., Ltd. official authorized agent, responsible for the United States Weidun VTON, Germany Lute LIT regulating valve product sales promotion, technical support With services, the main products are: imported regulating valve, imported electric regulating valve, imported pneumatic regulating valve, imported self-regulating valve, imported self-operated temperature regulating valve, imported self-operated flow regulating valve, imported self-operated pressure regulating valve, imported Steam regulating valve, imported pneumatic diaphragm control valve, imported three-way regulating valve, etc.; consulting hotline; 13760336133; Contact: Huang Gong; Weidun Website: http://;
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