regulating valve - Selection guide and replacement guide
Selection importance
Selection valve applications , in addition to the quality of the product itself , the user is installed correctly, use, maintenance , the correct calculation, selection is very important. Selection of calculation errors , it will affect the entire system can not even put into use or cause huge economic losses. Therefore, the user purchases , system designers must pay attention on the control valve selection should be experienced design institutes, research institutes, state Chung controlled valve technology professional engineer calculation, selection .
Selection Actuator
1 according to the site conditions are selected to perform the mechanical drive type: When the site can only provide gas supply and control signals , the selected pneumatic actuators ; When the scene can only provide power and control signals , selected electric actuator ; If the gas supply and power supply as well as sometimes no control signal , only selected force regulating valve .
2 features electric actuator : The advantage is the driving source ( power ) to facilitate the control circuit is simpler than the pneumatic actuator , the disadvantage is reliability, water proof protective performance , stability, life as pneumatic actuators , and high -volume cost recommended preferred pneumatic.
3 Features pneumatic actuator : the advantage of stable performance, protective , and can save significantly when the bulk cost, and light weight, long life , the disadvantage is relatively complex control circuit ( required gas supply piping and signal distribution lines ) , optional accessories cumbersome, high gas source if no single cost.
Select the type of structure
Structure type regulating valves are commonly used: single-seat valves, sleeve valves , valve seat , three-way valve straight stroke ( confluence , shunt ) , right angle valve , ball valve angle stroke O , V ball valve, butterfly valve.
Process parameters according to the site conditions and requirements , combined with the characteristics of the control valve in the following table to select a different structure :
Structure Type Features and use the occasion
Single seat valve Small seat leakage , allow pressure , suitable for general fluid , or both requires good sealing off function occasions.
Valve seat Unbalanced force is small, single-seat valves allow pressure than the large, but the channel complex than single-seat valve seat leakage and sleeve valve should be large . For larger pressure, tightness is not required for the occasion .
Sleeve valve Good stability, allow pressure large , easy to replace maintenance trim . For general fluid , the pressure drop , flow rate, adjustable wide range of dynamic stability, low noise, small cavitation corrosion , which combines the advantages of single-seat and two-seat .
Angle Valve There are single-seat and two structures in the form of a sleeve , a simple flow path , entrances, exits into a 90 degree angle to facilitate purification and cleaning. Right angle connector suitable for the occasion as well as highly viscous medium containing particles and other substances .
Three-way valve Linear three-way mixing valve and the valve is divided into two bypass valves , merging the two different media are mixed in different proportions or request into a medium , a medium sucked shunt ratio according to the type or requirements into two -way outflow valve is often used for both heating or cooling systems , heat exchangers.
V-ball Adjust better performance than the O- Ball , flow coefficient, allow a large pressure difference , sealing, compact structure, suitable for paper pulp , sewage, contain fiber, particles and other fluids.
O- Ball Flow coefficient , sealing, compact structure, but the flow characteristics of a single , he is just an approximation and butterfly as a percentage flow characteristic , worse than the performance of its structural adjustment . It is suitable for water containing a small amount of fluid particles , adjusting performance is not particularly stringent requirements and simultaneously cut off occasion.
Butterfly Flow coefficient, compact structure , large diameter range , light weight, low cost , but the flow characteristics of a single , as he and the O- Ball is just an approximate percentage of the flow characteristics , worse than the performance of its structural adjustment . It is suitable for water , air conditioning systems to adjust the beginning , the control characteristic is not particularly critical situations .
body materials and sealing materials choice
1 , aspects of the valve pressure rating , temperature and corrosion resistance , etc. should not be less than the required process connection pipes and styling products should be preferred manufacturer
2 , water vapor or water more wet gas and explosive media , should not use cast iron valves.
3 , when the ambient temperature is below -20 ℃ ( especially in the north ) , should not use cast iron valves.
4, strong corrosion , corrosion resistant alloy selection must be based on the type of media concentration , temperature, pressure difference , select the appropriate corrosion-resistant materials .
5 , the temperature of the lining material ( fluorine rubber, plastic , PTFE) the selection of the working medium , the pressure must satisfy the concentration range of the material, its physical and mechanical damage and to consider the operation of the valve ( such as cut damage ) .
6 , the typical special media should choose typical corrosion resistant alloy materials.
Select flow characteristics
1 , equal percentage flow characteristic .
2 , linear flow characteristics, divided into linear and parabolic .
Percentage of 3 , approximately equal flow characteristics.
failsafe mode of action and choice ;
1 electric control valve , mode choice : Electric open , electricity off type , fault protection ( required to maintain power ) , the signal is interrupted : fully closed , hold, fully open.
2 pneumatic control valve , mode of action options: open air , air -to-close , fault protection ( air source signal is interrupted ) : fully closed ( open air ) , full ( air -to-close ) .
(3) Self-pressure regulating valve , mode options: front control valves, pressure relief role play ; After the control valve , pressure regulator from the role .
Select accessories
When the control system is proposed for a variety of special valve requirements , the following must be optional accessories to meet these requirements:
An electrical positioning device receives the control signal for regulating the control valve to improve the performance characteristics of the work , to achieve the correct positioning.
2 , back to the hearing , also known as limit switches, valve position switch for display or working position valve stroke remote runtime feedback .
3 , for the purification of air filter regulator air source , adjust the air pressure.
4 , the solenoid valve to perform switching control of the air supply , ensure that the valve is in a power failure the valve opening degree of the desired safety position .
5, the hand wheel when the control system controller fails, the valve can be operated manually .
6 , valve position transmitter, the valve position timely motion to form a feedback signal to a remote control room or the receiving device .
7 , to secure his position pneumatic valve , also called the lock valve , control valve when the gas supply fails to keep the valve in the open position before the air supply failure .