Tag: control valves
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How to Size a Control Valve
Control valve sizing refers to the procedure determining the correct size of a valve body. A valve sizing equation for incompressible fluids is given by: Which is the same as: Where Cv is the valve flow coefficient/valve capacity P1 = Upstream fluid pressure P2 = Downstream fluid pressure ρ = Mass density of fluid Q…
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Steam Traps – Basic Features, Types & Applications
A steam trap is a control valve whose basic function is to allow condensate to flow, while preventing the passage of steam until it has given up its heat by condensing back to water; in other words, a steam trap is a self-contained valve which automatically drains condensate and discharges air and non-condensable gases from…
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Control Valve Selection Guide
Valves are manual or automatic fluid controlling elements in a piping system; in other words, valves isolate, switch, and control fluid flow in piping systems. They are constructed to withstand specific range of temperature, pressure, corrosion, and mechanical stress. Valves can be operated manually using levers or gear operators or remotely using electric, pneumatic, electro-pneumatic…
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Electro-Pneumatic Valve Positioners: Function & Features
Valve positioners are motion-control devices that are made in such a way to actively compare valve stem position against the control signal, adjusting the actuator diaphragm or piston till the correct stem position is achieved, that is, in a nutshell a valve positioner’s goal is to ensure the mechanical valve’s position matches the command signal…
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Valve Positioners: Function & Types
Basic Features of a Positioner Pneumatically operated valves depend on a positioner to take an input signal from the process controller and convert it to valve travel. In other words, a positioner is a motion control device made to actively compare the stem position against the control signal, adjusting the pressure to the actuator diaphragm…
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Directional Control Valves: Function & Principle of Operation
Directional control valves are used to regulate the flow rate of hydraulic fluid; they are also utilized in pneumatic systems for flow control. Directional control valve works by regulating the movement of the piston in the cylinder. It admits pressurized fluid to either end of the cylinder while providing a return path for fluid being…
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Key Factors to Consider in Selection of Valves
Valves are the final element in a control loop, and are critical in providing the correct flow. The valve, usually operates in very harsh conditions, and is one of the most costly elements in the process control system. Their selection and correct installation require both knowledge and experience. Understanding system requirements and manufacturers specifications is…
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Pneumatic Actuators
Valves cannot control a process by themselves. Manual valves require an operator to position them to control a process variable. Valves that must be operated remotely and automatically require special devices to move them. These devices are called actuators. Actuators may be pneumatic, hydraulic, electric solenoids or motors. In this article we look at specifically…