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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.
The servo valves of the World War II-era were similar to this — using a solenoid to drive a spool valve. Advancement of EHSVs took off in the 1950s, largely due to the adoption of permanent magnet torque motors as the first stage (as opposed to solenoids). This resulted in greatly improved response times and a reduction in power used to ...
After receiving an operation command, the actuator moves the valve in direction OPEN or CLOSE. When reaching the end position, an automatic switch-off procedure is started. Two fundamentally different switch-off mechanisms can be used. The controls switch off the actuator as soon as the set tripping point has been reached. This is called limit ...
The inside of an extremely large butterfly valve Duplex ball valve Three check valves in corrosion-resistant Hastelloy Stainless steel gate valve. Valves can be categorized into the following types, based on their operating mechanism: Ball valve, for on–off control without pressure drop. Ideal for quick shut-off, since a 90° turn completely ...
Diaphragm valves (or membrane valves) consists of a valve body with two or more ports, a flexible diaphragm, and a "weir or saddle" or seat upon which the diaphragm closes the valve. The valve body may be constructed from plastic , metal or other materials depending on the intended use.
Tilting-disc inconel check valve Check valve symbol on piping and instrumentation diagrams.The arrow shows the flow direction. Vertical lift check valve. A check valve, non-return valve, reflux valve, retention valve, foot valve, or one-way valve is a valve that normally allows fluid (liquid or gas) to flow through it in only one direction.