ACTUATOR: A fluid-powered or electrically powered device that supplies force and motion to a VALVE CLOSURE MEMBER.

AIR SET: Also SUPPLY PRESSURE REGULATOR. A device used to reduce plant air supply to valve POSITIONERS and other control equipment. Common reduced air supply pressures are 20 and 35 psig.

AIR-TO-CLOSE: An increase in air pressure to the ACTUATOR is required to cause the valve to close. This is another way of saying the valve is Fail Open or Normally Open.

AIR-TO-OPEN: An increase in air pressure to the ACTUATOR is required to cause the valve to open. This is another way of saying the valve is FAIL CLOSED or NORMALLY CLOSED.

ANSI: An abbreviation for the American National Standards Institute.

ANTI-CAVITATION TRIM: A special trim used in CONTROL VALVES to stage the pressure drop through the valve, which will either prevent the CAVITATION from occurring or direct the bubbles that are formed to the center of the flow stream away from the valve BODY and TRIM. This is usually accomplished by causing the fluid to travel along a torturous path or through successively smaller orifices or a combination of both.

API: An abbreviation for the American Petroleum Institute.

ASME: An abbreviation for the American Society of Mechanical Engineers.

ASTM: An abbreviation for the American Society for Testing and Materials.

BALANCED TRIM: A trim arrangement that tends to equalize the pressure above and below the valve plug to minimize the net static and dynamic fluid flow forces acting along the axis of the stem of a GLOBE VALVE. Some regulators also use this design, particularly in high pressure service.

BELLOWS SEAL BONNET: A BONNET which uses a BELLOWS for sealing against leakage around the valve plug stem.

BENCH SET: The proper definition for bench set is the INHERENT DIAPHRAGM PRESSURE RANGE, which is the high and low values of pressure applied to the diaphragm to produce rated valve plug travel with atmospheric pressure in the valve body. This test is often performed on a work bench in the instrument shop prior to placing the valve into service and is thus known as Bench Set.

BODY: The body of the valve is the main pressure boundary. It provides the pipe connecting ends and the fluid flow passageway. It can also support the seating surface and the valve CLOSURE MEMBER.

BONNET: The bonnet or bonnet assembly is that portion of the valve pressure retaining boundary which may guide the stem and contains the PACKING BOX and STEM SEAL. The bonnet may be integral to the valve body or bolted or screwed. The bonnet, if it is detachable, will generally provide the opening to the valve body cavity for removal and replacement of the internal TRIM. The bonnet is generally the means by which the actuator is connected to the valve body.

BOOSTER: A pneumatic relay that is used to reduce the time lag in pneumatic circuits by reproducing pneumatic signals with high-volume and or high-pressure output. These units may act as volume boosters or as amplifiers. A 1:2 booster will take a 3 to 15 psig input signal and output a 6 to 30 psig signal. It has also been shown that a booster may improve the performance of a control valve by replacing a positioner. It can provide the same stroking speed and can isolate the controller from the large capacitive load of the actuator.

BUBBLE TIGHT: A commonly used term to describe the ability of a control valve or regulator to shut off completely against any pressure on any fluid. Unfortunately, it is completely unrealistic. Control valves are tested to ANSI B16.104 and FCI 70-2-1976 which is the American National Standard for Control Valve Seat Leakage. This standard uses 6 different classifications to describe the valves seat leakage capabilities. The most stringent of these is Class VI which allows a number of bubbles per minute leakage, depending on the port size of the valve. The correct response to the question