Control valve interview question and answers

controlvalve

#1

What is a valve?

A valve is a device used to control the flow of fluid in a stream.

What is a control valve ?

A control valve changes the flow rate in the stream as a response to the controller output to change the manipulated variable. The controller can adjust the valve opening at any stage between ON & OFF.

What are check valves ?

Check valves allow flow only in one direction. If there is a higher pressure opposite to the allowed flow direction then the valve closes.

What is a Pressure relief valve?

Pressure relief valves are safety valves. Pressure relief valves are connected parallel to the mainstream of flow, when there is an excesses pressure above setpoint in the line, the relief valve opens and feedback the fluid to the compressor or tank.

What are Gate valves?

Gate valves are used as shut off valves. There is only two action for Gate valves, ON & OFF. Mostly Gate valves are manually operated in industries.

What is cavitation?

Cavitation can occur in valves when used in throttling or modulating service. Cavitation is the
sudden vaporization and condensation of a liquid downstream of the valve due to localized low
pressure zones.

When flow passes through a throttled valve, a localized low pressure zone forms immediately downstream of the valve. If the localized pressure falls below the vapour pressure of the fluid, the liquid vaporizes (boils) and forms a vapour pocket. As the vapour bubbles flow downstream, the pressure recovers and the bubbles violently implode causing a popping or rumbling sound similar to tumbling rocks in a pipe.

What is Flashing?

If the local pressure within the restricted flow area drops below the vapor pressure of the liquid, which is a condition called the “vena contracta,” vaporization occurs (i.e., vapor bubbles would form in the liquid). If the downstream pressure remains below the vapor pressure, the process is said to be a flashing service,