GLOSSARY
OF TERMS

A trim arrangement that tends to equalise the pressure above and below the valve plug to minimise the net static and dynamic fluid flow forces.

A valve where the closing member is a spherical ball. Closure is achieved by turning the ball.

A bonnet which uses a bellows for sealing against leakage around the valve plug stem.

The proper definition for bench set is the inherent diaphragm pressure range, which defines the high and low values for 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.

The body of the valve is the main pressure boundary. It provides the pipe connecting ends and the fluid flow passageway.

The bonnet is that portion of the valve pressure retaining boundary that 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.

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 3-15 psig input signal and output a 6-30 psig signal.

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 totally 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 six different classifications to describe a valve’s 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 “Will that valve go ‘Bubble Tight’?” is to say that it is tested to meet Class VI shutoff requirements.

Profiles that are machined on the ends of the pipework components, to allow the joining of components by circumferential weld.

A valve with a circular body and a rotary motion disk closure member which is pivotally supported by its stem. Butterfly valves come in various styles, including eccentric and high-performance valves. Butterfly valves are high recovery valves and thus tend to induce cavitation in liquid services at much lower pressure drops and fluid temperatures than the globe style valve. Due to instability problems with the older design butterfly valves, many people will limit the travel of the valve at 60 degrees of rotation on throttling services. This can also help to prevent cavitation problems.