Close-off pressure is an important parameter that defines the differential pressure required to seat the valve and stop flow completely and is a function of the hydraulic design of the system and the criteria for deciding the type of valve actuator. Typically, actuators are either electronic or pneumatic. The significant performance differentiator between the two is speed of operation. While the electric actuators are better known for their high levels of precision the pneumatic actuators are very popular due
to their relatively low cost, high power output, and reliability. The choice of pneumatic or electric actuators involves
an evaluation of performance, component costs,
system costs, and productivity gains. Each has inherent advantages and disadvantages. Refer to Section 1 fora detailed comparison.
Note- Automatic control valves are not designed to produce tight shutoff and will likely to be prone to small amount of leakage when closed. Consequently, most control valve installations include block valves or manual valves which can be turned when complete shutoff is needed.
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