GLOSSARY
OF TERMS

Steam at a temperature equal to the boiling point of water and condensing temperature of steam, at the specified pressure.

The contact force between the seat and the valve plug. When an actuator is selected for a given control valve, it must be able to generate enough force to overcome static, stem and dynamic unbalance with an allowance made for seat load.

A part of the flow passageway that is used in conjunction with the closure member to modify the rate of flow through the valve.

A device used to reduce noise generated by flowing gases.

A connection made by entering a pipe into a matching socket in the end of a valve fitting, and welding the two together.

A term used to describe a valve trim with an elastomeric or plastic material used either in the value plug or seat ring to provide tight shutoff with a minimal amount of actuator force. A soft-seated valve will usually provide CLASS VI seat leakage capability.

The local speed of sound in the fluid.

A term applied to a Class designated threaded or weld end valve, where the body and cover have been subjected to non-destructive examination (NDE) and any defects removed. This allows the valve to have a higher pressure capacity than a standard class valve.

A valve whose body is split. This design allows for easy plug and seat removal. Split-bodied valves are made in both the straight-through and angle versions.

The net force produced on the valve stem by the fluid pressure acting on the closure member and stem within the pressure retaining boundary. The closure member is at a stated opening with a stated flow condition. This is one of the forces that an actuator must overcome.

Also called Stellite 6 or Alloy 6. A material used in a valve trim known for its hardness, wear and corrosion resistance. Stellite is available as a casting, barstock material and may be applied to a softer material such as 316 stainless steel by means of spray coating or welding.

The valve plug stem is a rod extending through the bonnet assembly to permit positioning of the plug or closure member. The actuator stem is a rod or shaft which connects to the valve stem and transmits motion or force from the actuator to the valve.

A guide bushing closely fitted to the valve stem and aligned with the seat. Good stem guiding is essential to minimise packing leakage.

See travel.

The subsea manifold is the distribution part of a subsea installation. A subsea manifold is a large metal piece of equipment, made up of pipes and valves and designed to transfer oil or gas into a pipeline. 

Subsea technology is a general term for equipment, technology, and methods employed in marine biology, undersea geology, offshore oil and gas developments and offshore wind power industries. 

Subsea trees monitor and control the flow from a subsea well. Fixed to on top of the well, subsea trees can also manage fluids or gas injected into the well. 

The pressure at the supply port of a device such as a controller, positioner or transducer. Common values of control valves supply pressure are 20 psig. for a 3-15 psig. output and 35 psig. for a 6-30 psig. output.