Valve Terminology - IV

Safety-relief valve:

A pressure-relief valve characterized by rapid opening pop action, or by opening generally proportional to the increase in pressure over the opening pressure.

Safety valve:

A pressure-relief valve actuated by inlet static pressure and characterized by rapid opening or pop action.

Seat:

The portion of the valve against which the closure member presses to effect shutoff.

Seat ring:

A separate piece inserted in the valve body to form a seat against which the valve-closure member engages to effect shut-off. Set pressure: The inlet static pressure of the system at which a relief valve starts to open, or safety valve pops open.

Short pattern valve:

A valve that has face-to-face or end-to-end dimension for a short pattern design according to standard ASME B16.10.

Steam working pressure (SWP):

The maximum rated or working pressure corresponding to the steam temperature that must not be exceeded when valve is used in steam service. It is marked with S, SP, or SWP on the valve.

Stroke:

 The amount of travel the valve-closure member is capable of from a fully closed position to a fully open position or vice versa. In linear-motion valves it is expressed in in (mm) and in degrees, 0 to 90, for rotary motion valves.

Throttling:

The process of regulating the fluid flow rate or pressure by controlling the position of the closure member between the full-open and full-closed positions.

Trim:

Functional parts of a valve which are exposed to the line fluid. Usually refers to the stem, closure member and, seating surfaces. The removable or replaceable valve metal internal parts that come in contact with the flow medium are collectively known as valve trim. Valve parts such as body, bonnet, yoke, and similar items are not considered trim.

Venturi port:

A valve bore or port that is substantially smaller than the full port, approximately 40 to 50 percent of full port. It is normally found in plug valves.

Wafer body:

A valve body that has a short face-to-face dimension in relation to pipeline diameter and is designed to be installed between two flanges using special length studs and nuts.

Wedge:

A gate valve–closure member with inclined sealing surfaces which come in contact with valve-seating surfaces that are inclined to the stem centerline. Wedge is available in solid, split, and flex designs.

Yoke:

That part of the valve assembly used to position the stem nut or to mount the valve actuator.

Yoke bushing, yoke nut:

Yoke nut, yoke bushing, or stem nut is the valve part that is held in a recess at the top of the yoke through which the stem passes. It converts rotary-actuating effort into thrust on the valve stem.