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A control valve is a valve used to control fluid flow by varying the size of the flow passage as directed by a signal from a controller. [1] This enables the direct control of flow rate and the consequential control of process quantities such as pressure , temperature , and liquid level.
A petcock is a small shut-off valve used to control the flow of liquid or gas.Historically, petcocks were threaded valves controlled by a butterfly handle; [citation needed] modern petcocks are typically ball valves.
A common example is the Johnson bar-controlled parking brake found on many trucks and buses. Johnson bar is also the North American term for a steam engine's reversing lever, used to control the valve gear. [1] [2] The forward/reverse lever on Caterpillar tractors is also called a Johnson bar.
Isolation valves must effectively stop the passage of fluids. [4] Gate valves, ball valves and plug valves are generally considered to provide tight and effective shut-off. Globe valves and Butterfly valves may not be tight shut-off due to wear on the plug or the seat, or due to their design, and may not be appropriate to provide effective ...
Control valves can also work with hydraulic actuators (also known as hydraulic pilots). These types of valves are also known as automatic control valves. The hydraulic actuators respond to changes of pressure or flow and will open or close the valve. Automatic control valves do not require an external power source, meaning that the fluid ...
The blue valve body is visible in-line with the pipe. The valve actuator opens or closes the butterfly disc of the valve based on electrical signals sent to the actuator. Another valve actuator is visible in the background, with windows to indicate the valve position. A valve actuator is the mechanism for opening and closing a valve. Manually ...