Control Valves Match Size with Application 2

Here are two good articles about control valve sizing and application. If you deal with control valve selection and sizing then you will find them very informative.

http://www.manufacturing.net/ctl/article/CA192829

http://www.manufacturing.net/ctl/article/CA192621

 

[SamHui]

do anyone know what is the difference between control valve and butterfly valve??? THanks.

 

[JimCasey]

SamHui: A butterfly valve can be a control valve, but it should be matched carefully to the capacity needs of the system. Generally, a full-sized butterfly valve will have vastly too much capacity and you will find that the control point will correspond to having the valve open very slightly. Rubbber-lined butterfly valves have excessive friction at small openings, and resolution is lost both by the tiny amount of available motion and the large amount of resistance to motion.
Double-offset butterfly valves are broken out of the seat by 10 degrees rotation so the friction goes away and control is much improved.

Butterfly valves have a dynamic torque peak at around 70 degrees open, also, and moving past that peak can cause problems as the actuator torque drops off rapidly.

Size your butterfly valve to throttle between 20 degrees open and 60 degrees open. Differential pressure when at max flow should be 1 bar or less, to prevent excessive velocity. Use a rack and pinion actuator (not diaphragm) one size larger than you would normally use, and be sure to use a good positioner and a clamped coupling.

 

[rjudy55]

This site is very helpful and contains a lot of good info on valves.

http://www.valvebid.com/index2.asp

If you need any bids on valves for any state go to

http://www.valvebid.com