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Device used to open or close or control valves. Key types are electrical, hydraulic and pneumatic. Movement may be quarter-turn or multi-turn. Actuators may be used when (i) valves are remotely located (eg, on pipelines) (ii) valves are located in hazardous areas (iii) manual operation would be time-consuming (eg, with larger valves)

Air valves
Valve that is used to control the flow rate of air.

Back pressure
The pressure exerted on the downstream side of a valve .

Ball valve
Normally a quarter-turn valve with a ball type closing element held between two seats. Characteristics include quick opening and tight shut-off. Ball valves are widely used as on/off valves in the chemical process and other industries. Special designs (with V notches ) are available for throttling applications. Larger valves with heavier balls (eg, on pipelines) may use trunnions to help support the ball and prevent damage to soft internals. Designs are typically, one, two or three piece.

Sealing device which prevents line media leaking between the stem and the body.

Bypass valve
A small bore valve fitted in parallel to a larger main valve. Bypass valves are used to reduce the differential pressure across the main valve before this latter valve is opened (as otherwise this larger, more expensive valve, may suffer damage to internal components).

Butterfly valve
A quarter-turn valve which has a circular disk as its closing element. The standard design has the valve stem running through the disk, giving a symmetrical appearance. Later designs off-set the stem, so that the disk ‘cams’ into the valve seat. Advantages include less wear and tear on the disk and seats, and tighter shut-off capabilities. Many design types are available including inexpensive Teflon or resilient seats for use in water (treatment) plants. More expensive metal seats can be used where high temperatures or aggressive chemicals are encountered. So-called “High Performance” butterfly valves which offer zero leakage designs and have been applied in both the chemicals and hydrocarbon processing sectors.

Check valve
A valve that is designed to allow the fluid to flow in a given direction but closes to prevent backflow. Types include swing check, tilting disc check and wafer check. Check valves (also called non-return valves) are usually self-acting.

Control valve
A valve which regulates the flow or pressure of a fluid. Control valves normally respond to signals generated by independent devices such as flow meters, temperature gauges, etc. Control valves are normally fitted with actuators and positioners. Pneumatically-actuated globe valves are widely used for control purposes

Cryogenic valve
These are valves suited for use at very low temperatures (cryongenic service)

Diaphragm valve
A bi-directional valve which is operated by applying an external force to a flexible element, or diaphragm (typically an elastomer). Diaphragm valves may be used for slurries (where other valve designs might clog) or in hygienic applications.There are several types of these valves but the general operation is the same.

Diverter valve
A valve which can change the direction of the flow of a medium to two, three or more different directions. This will save the user having to connect several single valves and piping together to achieve the same thing

Double block and bleed
A valve configuration in which positive shut-off is achieved at both the inlet and outlet sides. A small port is fitted to discharge fluid or gas in the intermediate space. This port can help a user check if the valve is leaking.

Electric actuator
Actuator which uses an electric motor to operate the valve stem.

Extended bonnet
Used when the media is at high or low temperatures, to avoid damage to the sealing elements.

Float valve
A valve which automatically opens or closes as the level of a liquid changes. The valve is operated mechanically by a float which rests on the top of the liquid.

Full bore
Term used e.g. of a ball valve, to indicate that the internal diameter of the valve opening is the same as that of the piping to which it is fitted as opposed to "Reduced Bore"

Gate valve
A multi-turn valve which has a gate-like disk and two seats to close the valve. The gate moves linearly, perpendicular to the direction of flow. This type of valve is normally used in the fully opened or fully closed position; it is not suited to throttling applications. Gate valves provide robust sealing, and are used extensively in the petrochemicals industries. This class of valves also includes knife gate valves, conduit gate valves and wedge gate valves. Knife gate valves have much thinner gates with a knife-like edge, making them suited to use with floating solids, eg, as in the pulp & paper industries. Conduit gate valves have a rectangular disk as the closing element. One half of the disk is solid, to close the valve, the other has a circular port, which can be used to open the valve. Wedge gate valves have a wedge-shaped gate which ‘wedges’ between floating seats to close the valve tightly.

Used to ensure easier operation of larger valves by requiring less torque to open or close and are used when people want to use smaller actuators or use less force to open or close.

Globe valve
A multi-turn valve with a closing element that moves perpendicularly to the valve body seat and generally seals in a plane parallel to the direction of flow. This type of valves is suited both to throttling and general flow control.

Hydraulic actuator
A device fitted to the valve stem than uses hydraulic energy to open and close the valve. Depending on the configuration, the hydraulic fluid may both open and close the valve, or just open the valve. Hydraulic actuators can also incorporate springs or compressed air/ gas circuits

Jacketed valves
This valve is design incorporates a so-called jacket around the valve body. Steam is introduced into the jacket to keep the fluids being controlled at the required temperature.

Line blind
A pipeline shut-off device, whereby a flat disk is forced between two flanges.

Multi-ported valves include additional inlet/outlet ports, to allow fluids to be directed. The ball and plug valve types are ideally suited to multi-port designs.

Category of valves (such as gate, globe, needle) which require multiple turns of the stem to move the valve from the fully open to the fully closed positions. Also known as linear valves.

Needle valve
This multi-turn valve derives its name from the needle-shaped closing element. The design resembles that of the globe valve. Typically available in smaller sizes, they are often used on secondary systems for delicate control and shut off e.g with analysers

Penstock valve
A type of simple gate valve, used to contain fluids in open channels. Often found in waste water treatment plants.

Pilot valve
Small valve requiring little power which is used to operate a larger valve.

Pinch valve
A valve in which a flexible hose is pinched between one or two moving external elements to stop the flow. This valve is often used in slurry and mining applications, as its operation is not affected by solid matter in the medium.

Plug valve
This multi-turn valve derives its name from the rotating plug which forms the closing element. The plug may be cylindrical or truncated.

Pneumatic actuator
A device fitted to the valve stem than uses air or gas to open/close or regulate the valve. Depending on the configuration, the compressed air may both open and close the valve, or just open the valve. In that latter case, a spring will typically be fitted inside the actuator to shut or open the valve.

Devices that help control the opening and closing of valves remotely by controlling pneumatic or hydraulic elements. Positioners can be controlled by adjusting currents to its circuits or by using air. More and more positioners have feedback control options

Pressure reducing valve
A self-operating valve used to reduce any excess pressure in a system, for example- steam. Also known as a PRV. The valve opens if the internal pressure exceeds that holding the valve disc onto the seat.

Quarter-turn Valve
Category of valves (such as ball and plug valves) which require just a 90 degree turn of the stem to move from the fully open to the fully closed positions.

Reduced bore
Indicates that the internal diameter of the valve is lower than the piping to which the valve is fitted as opposed to full bore (see full bore)

Regulating valve
This valve type is used to regulate flows to provide a constant pressure output.

Sampling valve
A valve which is fitted to a pipeline to allow samples of a fluid to be withdrawn for analysis

Solenoid valve
Solenoid valves are operated by an electrical solenoid. They are often deployed as piloting valves, i.e., fitted to actuators which in turn control larger valves.

Subsea valve
A valve which is designed for use in sea water. For example, installed in a pipeline on the sea bed.

Swing check Valve
This non-return valve has a hinged disk as the closing element.

Tank valve
A valve arranged for fitting at the bottom of a tank or process vessel.

Wellhead valve
Wellhead valves are used to isolate the flow of oil or gas at the takeoff from an oil or gas well. The design is usually a plug or gate valve.

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