❷Choice of Actuator

     (1) The simplest is the pneumatic film type, followed by the piston type, and finally the electric type.

     (2) The main advantage of electric actuators is that the driving source (power supply) is convenient, but the price is high, reliability, waterproof and explosion-proof are not as good as pneumatic actuators, so the pneumatic type should be preferred.

     (3) The old electric actuator is cumbersome, and the electronic, small and highly reliable electric actuator produced by Shanghai Chuanhu Valve is provided (the price is correspondingly high).

     (4) The old ZMA and ZMB thin-film actuators can be eliminated and replaced by multi-spring light actuators (the performance is improved, and the weight and height are reduced by about 30%).

     (5) There are many varieties and specifications of piston actuators, and the old, big and stupid ones are no longer recommended, but a new light structure is selected.

❸ Material selection

    (1) The valve body pressure rating, operating temperature and corrosion resistance should not be lower than the requirements of the process connection pipeline, and the manufacturer's finalized products should be preferred.

    (2) Cast iron valves are not suitable for water vapor or wet gas with more water 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 the Cartesian coordinates formed by the medium temperature and pressure difference with serious cavitation and erosion, when the temperature is 300°C and the pressure difference is 1.5MPa in the area beyond the line connecting the two points, the throttling sealing surface should be Choose wear-resistant materials, such as cobalt-based alloys or surface surfacing Stellite alloys.

    (5) For strong corrosive media, the selection of corrosion-resistant alloys must be based on the type, concentration, temperature and pressure of the medium, and appropriate corrosion-resistant materials must be selected.

    (6) The valve body and the throttling part are treated separately. The throttling speed of the valve body wall is small and a certain degree of corrosion is allowed. The corrosion rate can be about 1mm/year; the throttling part is eroded by high speed and corroded, which will cause leakage and increase. If it is 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 use range of the material, and consider the physical and mechanical damage (such as shear damage) of the valve when it acts. .

    (8) The vacuum valve should not be lined with rubber or plastic in the valve body.

    (9) The two-position shut-off valve of the water treatment system should not be made of rubber-lined materials.

    (10) Typical corrosion-resistant alloy material selection for typical media:

    a. Sulfuric acid: 316L, Hastelloy, Alloy 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: Inconel, 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 tetrafluoroethylene, which is called "corrosion-resistant king". Therefore, the PTFE corrosion-resistant valve should be selected first, and the alloy should be selected only in the case of unavoidable circumstances (such as temperature>180℃, PN>1.6).

❹ Choice of flow characteristics

  The following are preliminary selections. For detailed selections, please refer to the special materials:

     (1) When S>0.6, logarithmic characteristic is selected.

     (2) The logarithmic characteristic is selected when working with small opening and when the unbalanced force changes greatly.

     (3) The required adjusted parameter reflects the straight line when the speed is fast, and the logarithm when it is slow.

     (4) The linear characteristic of the pressure regulation system is optional.

     (5) The linear characteristic of the liquid level adjustment system is optional.

❺Choice of action

     (1) It is commonly used in foreign countries to indicate that it is open or closed under fault, that is, fault open and fault closed, which is exactly the opposite of my country's air open and air closed.

     (2) The new light valve and fine small valve no longer emphasize the positive and negative effects of the execution machinery, so they must be marked on the endnote.

     B (air to close) K (air to open)

     Choice of spring ranges:

     (1) The first is to select the spring range, and also to determine the working spring range.

     (2) Determining the working spring range involves calculating the output force to overcome the unbalanced force. If there is any difficulty, the conditions (mainly the pressure difference when the valve is closed) should be told to the manufacturer to assist in the calculation and adjustment of the spring and the working range before leaving the factory (at present, many manufacturers do not do the calculation at all).

❻ choice of flow

     (1) At the throttling port, the flow of the medium in the opening direction of the valve core is flow opening, and the flow in the closing direction is flow closing.

     (2) The choice of flow direction is mainly single-sealed regulating valve, which includes three categories: single-seat valve, angle valve, and single-sealed sleeve valve. It is based on the specified flow direction (such as double seat valve, V ball) and arbitrary flow (such as O ball).

     (3) When dg>15, the flow is usually selected to be open. When dg≤15, the small-diameter valve, especially the high-pressure valve, can be selected to be closed to improve the service life.

     (4) Optional flow and close for the two-position switch valve.

     (5) If the flow-closed valve oscillates, change it and the flow-open type can be eliminated.

❼Choice of filler

     (1) Commonly used in regulating valves are tetrafluoro "V"-shaped packing and graphite "O"-shaped packing.

     (2) The tetrafluoro packing has small friction, but has a short temperature difference and short life; the graphite packing has large friction, but has good temperature resistance and long life; it is recommended to choose graphite packing under high temperature and for valves with positioners.

     (3) If the tetrafluoro packing is often replaced, graphite packing can be considered.

❽Choice of accessories

      (1) The accessories of the regulating valve mainly include: positioner, converter, relay, booster valve, position retaining valve, pressure reducing valve, filter, lubricator, travel switch, position transmitter, solenoid valve, Handwheel mechanism.

     (2) The accessories play a supplementary function and ensure the operation of the valve. Increase when necessary, not increase when unnecessary. Adding accessories when not necessary increases the price and reduces reliability.

    (3) The main function of the positioner is to improve the output force and action speed. When these functions are not required, it can be omitted. It is better not to bring the positioner.

    (4) For fast response systems, the valve does not act quickly, and a converter is optional.

    (5) For strict explosion-proof occasions, optional: electrical converter + pneumatic positioner.

    (6) The solenoid valve should choose a reliable product to prevent it from not moving when it is required to act.

    (7) In important occasions, it is recommended not to use the handwheel mechanism to prevent human error.

    (8) It is best to provide by the manufacturer and supply the assembly on the valve to ensure the reliability of the connection between the system and the assembly.

    (9) When ordering, the name, model, specification, input signal, output signal, etc. of the accessories should be provided.

    (10) To reiterate: Please pay attention to the importance of these "little things", especially reliability. If necessary, pneumatic components such as solenoid valves can be provided.