Valve type selection:
(1) Determine the nominal pressure. Instead of using Pmax to set the PN, the temperature, pressure, and material conditions are used to find the corresponding PN from the table and satisfy the PN value of the selected valve.
(2) The determined valve type, the leakage amount meets the process requirements.
(3) For the determined valve type, the working pressure difference should be less than the allowable pressure difference of the valve. If not, the valve should be considered or selected from a special angle.
(4) The temperature of the medium is within the operating temperature range of the valve, and the ambient temperature meets the requirements.
(5) Consider the anti-blocking problem of the valve according to the unclean condition of the medium.
(6) Consider the corrosion resistance of the valve according to the chemical properties of the medium.
(7) Consider the erosion and wear resistance of the valve according to the differential pressure and the medium containing the hard material.
(8) Performance and price ratio considering comprehensive economic effects. There are three issues to consider:
a. The structure is simple (the simpler the higher the reliability), the maintenance is convenient, and the spare parts have sources;
b. Service life
c. price.
(9) Preferred order.
Butterfly valve - single seat valve - double seat valve - sleeve valve - angle valve - three way valve - ball valve - eccentric rotary valve - diaphragm valve.
Executive agency selection:
(1) Zui is simple pneumatic type, followed by piston type, and after Zui is electric type.
(2) The main advantage of the electric actuator is that the drive source (power supply) is convenient, but the price is high, the reliability, waterproof and explosion-proof are not as good as the pneumatic actuator, so the pneumatic type should be preferred.
(3) The old electric actuator is cumbersome, and we have provided electronic precision small and high-reliability electric actuators (the price is correspondingly high).
(4) The old ZMA and ZMB film actuators can be eliminated, replaced by a multi-spring light actuator (performance improvement, weight and height drop of about 30%).
(5) There are many varieties of piston actuators. The old, big and stupid suggestions are no longer used, but the light new structure is selected.
Material selection:
(1) The pressure resistance grade, service temperature and corrosion resistance of the valve body should not be lower than the requirements of the process connection pipe, and the manufacturer's styling products should be preferred.
(2) Water vapor or wet air containing more water and flammable and explosive medium should not be used.
(3) When the ambient temperature is lower than -20 °C (especially in the north), it is not suitable to use cast iron valves.
(4) In the Cartesian coordinates of the medium temperature and pressure difference where the cavitation and erosion are more serious, the temperature is 300 ° C, and the pressure difference is 1.5 MPa. Wear-resistant materials such as cobalt-based alloys or surface-stacked steels are used.
(5) For highly corrosive media, the selection of corrosion-resistant alloys must be based on the type, concentration, temperature and pressure of the medium to select suitable corrosion-resistant materials.
(6) The valve body and the throttle member are treated separately, the throttle wall of the valve body has a small throttle speed and allows a certain corrosion, and the corrosion rate can be about 1 mm/year; the throttle member is subjected to high-speed erosion and corrosion, and the bow is increased. Large, its 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 physical and mechanical damage (such as shear failure) when the valve is actuated. .
(8) Vacuum valve should not be used to line the rubber and plastic structure of the valve body.
(9) The two-way shut-off valve of the water treatment system should not be made of rubber-lined 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: Inconel and Hastelloy.
g. Urea: 316L.
h. Caustic soda: Monel.
i. Chlorine: Hastelloy C.
j. Seawater: Due to Niel, 316L.
(11) So far, Zui's versatile corrosion-resistant material is PTFE, which is called “corrosion-resistant king”. Therefore, the PTFE corrosion-resistant valve should be selected first, and the alloy should be selected only when it is necessary (such as temperature >180 °C, PN>1.6).
Choice of flow characteristics:
The following is a preliminary selection. For detailed selection, see the special information:
(1) When S>0.6, the logarithmic property is selected.
(2) When the small opening degree is working and the imbalance force changes greatly, the logarithmic characteristic is selected.
(3) The required adjusted parameters reflect the line when the speed is fast, and the logarithm when the speed is slow.
(4) The linear characteristics of the pressure regulation system are optional.
(5) Optional linear characteristics of the liquid level adjustment system.
Mode of action selection:
(1) The common faults in foreign countries are turned on or off to indicate that the fault is open and the fault is closed. It is opposite to the air opening and air closing in China. The fault opens corresponding to the gas closing valve, and the fault close corresponds to the gas opening valve.
(2) The new light-duty valve and fine-sized valve have not emphasized the positive and negative effects of the execution of the machine, so it must be marked on the endnote.
B (gas shut) K (air open)
Spring range selection:
(1) First, select the spring range and determine the working spring range.
(2) Determining the working spring range involves calculating the output force to overcome the imbalance force. If there is any difficulty, the condition (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 working range (currently, many manufacturers do not calculate at all).
Flow direction selection:
(1) At the orifice, the medium flows in the direction in which the spool is opened, and flows in the closing direction.
(2) The choice of flow direction is mainly a single-sealed type regulating valve, which has three categories: single-seat valve, angle valve, and single-seal sleeve valve. It is intended to regulate the flow direction (such as double seat valve, V ball) and any flow (such as O ball).
(3) When dg>15, the flow is usually selected. When the dg≤15 small-diameter valve, especially the high-pressure valve, can be closed to improve the life.
(4) The two-way switch valve can be selectively closed.
(5) If the flow-closing valve oscillates, change it, and the flow-open type can be eliminated.
Packing choice:
(1) The regulating valve is commonly used as a tetrafluoro "V" shaped packing and a graphite "O" shaped packing.
(2) The PTFE filler has small friction, but the temperature difference is short and the service life is short; the graphite filler has large friction, but the temperature resistance is good and the service life is long; the graphite filler is recommended for the valve at high temperature and with the positioner.
(3) If the PTFE filler is changed frequently, graphite filler can be considered.
Selection of attachments:
(1) The accessories of the regulating valve mainly include: positioner, converter, relay, booster valve, retaining valve, pressure reducing valve, filter, oil mister, travel switch, position transmitter, solenoid valve, Handwheel mechanism.
(2) The accessory functions to supplement the function and ensure the operation of the valve. If necessary, increase, unnecessary increase. Increasing attachments when not necessary increases price and reliability.
(3) The main function of the positioner is to increase the output force and the speed of movement. When these functions are not needed, it is not necessary to bring it, not with a positioner.
(4) For fast response systems, do not operate the valve quickly, optional converter.
(5) Strict explosion-proof occasions, optional: electrical converter + pneumatic positioner.
(6) Solenoid valve should choose a reliable product to prevent it from acting when it is moving.
(7) It is recommended that the hand wheel mechanism is not used in important occasions to prevent human error.
(8) Zui is supplied by the manufacturer and the assembly is supplied 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 accessory should be provided.
(10) Reaffirm: Please note the importance of these “small things”, especially reliability, and if necessary, pneumatic components such as solenoid valves.