Control Valve Manufacturers

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About Control Valves

Control valves (also known as proportional valves) are designed to respond to signals from controlling mechanisms to regulate conditions such as pressure, flow, temperature, and liquid level. Conditions are monitored by sensors that compare operating values to standard values within an accepted range, and controllers respond by opening or closing the valve a certain amount to compensate if the reading is not within those bounds. The valves are moved via electrical, hydraulic or pneumatic inputs, which direct positioners to move the valve actuators.

A control valve is an important part of a process in which control loops are employed to maintain process variables such as pressure, flow, level, temperature, and other factors within a required operating range to ensure the quality of an end product. Such processes are subject to load disturbances, and control valves manipulate flow to reduce or eliminate the effect of these disturbances.

A control valve assembly usually is made up of the valve body, an actuator that responds to a controller to move the valve, internal trim, and there may be additional accessories such as positioners, transducers, supply pressure regulators, manual operators, snubbers, or limit switches.

Types of Control Valves

Angle seat piston valves use a piston actuator to lift a seal in a linear motion. This valve is pneumatically-controlled. If the valve is spring-loaded, the spring returns the seal to its original position when the piston is deactivated. In a double-action angle seat piston valve, the action of the piston provides motion in both directions. These valves are ideal for applications in which high temperatures and/or large flow rates are encountered. The valve seat is set at an angle to provide maximum flow when unseated. Examples of angle valves are cage-style valve bodies and disk-stack style valve bodies.

A globe valve (sometimes known as a stop valve in plumbing) was named for its originally spherical body, although that general shape is not necessarily a requirement today. This valve uses an internal plug or disc attached to a stem. The stem is turned via a screw to seat it or unseat it in an internal baffle, thus regulating the flow through the valve.

A rotary valve uses the rotation of the passages of a plug to control flow. As the plug moves, it presents a changing pathway for the flow material, either altering the length of the pathway (as in a musical instrument) or allowing for the introduction or expelling of materials from two chambers.

A gate valve or knife valve uses linear motion to slide a plate or disc into place to control or stop flow. A gate control valve uses either parallel or wedge-shaped discs. The parallel gate uses a flat disc between two parallel seats. The knife valve has a sharper edged disc that enables it to cut through remnant solids (such as slurries) to completely close.

A needle valve has a tapered point on a stem that passes through the seat until a seal is made.

A pinch valve, as the name implies, is "pinched" closed via a mechanism or pressure, to stop or regulate flow. Therefore these are usually made of a flexible or elastic type material.

A diaphragm valve is similar to a pinch valve, but uses an internal diaphragm that is pushed into the valve seat.

Plug valves are simple stop or control valves that are also known as cock or stop-cock valves.

Butterfly valves and ball valves can also be considered control valves in some cases, as that type of construction is employed in many control valves assemblies.

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