When sizing actuators for control or automated on-off valves what is the general rule?
while this seems like a simple question actuator sizing is probably one of the most misunderstood components of valve sizing. Actuator sizing is based on providing sufficient energy to overcome the process pressure P1, P2. In some cases sizing can be calculated on the differential pressure but the preferred practice is to use the maximum shut-off pressure (P1) and assume the downstream pressure (P2) is zero. this provides a safeguard in the event there is a process upset and the valve must close. When sizing actuators for highly viscous service, a process with entrained solids or even dry gases such as O2 it is wise to multiply the calculated shut-off of the actuator size by 1.5. this provides a safety margin needed to overcome the dynamic forces of these unique mediums to close the valve. When calculating friction loading from packing, such as grafoil, it is wise to multiply the calculated actuator sizing by a factor of 1.15. It is also recommended that when using high friction packin
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