Speed limiter or speed controller on shutdown valves

The term of speed limiter or speed controller on shutdown valves is referring to an adjustable flow control valves. This flow control valves usually also called as needle valves. The operating principle is the same with a globe control valves except it utilize its small plug to control the opening of its internal orifice.

In most application the flow control valve is putted in the downstream of the solenoid valve right before the instrument air supply line to the actuator. With this configuration, if we want to slower the valve opening, we just need to adjust this flow control valves so that the flow of instrument air supply to the actuator is slow. Otherwise, if we want to make the opening or closing of the valve faster, we just need to adjust this flow control valves so that the flow of instrument air supply is faster.

In most application, this flow control valves is already equipped with an integral check valves. This check valves will makes the flow in opposite direction of the needle valve flow faster than goes through the needle valves. By using this integral check valves, the instrument air venting from the actuator will be faster. In other words, when the solenoid valve energized, the instrument air supply will be controlled by the needle valve to the actuator. But when the solenoid valve de-energized, the instrument air from the actuator will be vented through the check valve instead of through the needle valve again (see below picture).

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