The image below shows how a control valve can be used to control rate of flow in a line. The "controller" receives the pressure signals, compares them with pressure drop for the desired flow and if the actual flow is different, adjusts the control valve to increase or decrease the flow.
Comparable arrangements can be devised to control any of numerous process variables. Temperature, pressure, level and flow rate are the most common controlled variables.
VALVE TYPES AND TYPICAL APPLICATIONS
|Valve type||Service and Function|
|Globe||YES||YES||NO||YES (note 1)|
|Ball||YES||(note 3)||NO||YES (note 4)|
|Plug||YES||(note 3)||NO||YES (note 4)|
|Service and Function|
DC = Directional Change
IOS = Isolation or Stop
PR = Pressure Relief
TH = Throttling
Only angle-globe valves can be used for a 90-degree change in direction of flow.
Check valves (other than the stop-check valves) stop flow only in one (reverse) direction. Stopcheck valves can be and are used as stop, block, or isolation valves, in addition to being used as a check valve.
Some designs of ball-and-plug valves (contact the valve manufacturer) are suitable for throttling service.
Multiport ball-and-plug valves are used for changing the direction of flow and mixing flows.
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