What is a valve?

A valve is a device that regulates and controls the flow of a fluid (gas, liquids, fluidized solids, or slurries) by opening, closing, or partially obstructing various passageways.

What are some components that describe a valve?

Body – The body is a key element: It contains the moving components in contact with the fluid and must withstand the pressure existing in the piping system.

Disk and Seat – The disk provides the capability for permitting and prohibiting fluid flow, in some designs the body is machined to serve as the seating surface and seal rings are not used.

Bonnet – The very top of the valve body which fastens (bolts) onto the body, thereby retaining the internals of the vavle, providing support and stability for the actuation and accessories.

Stem – The stem is linked to the valve actuator or to the manual handwheel (or lever), at one end, and is connected to the valve disc on the other end. There are 5 main types: Rotary, sliding, rising with outside screw, rising with inside screw, and non-rising with inside screw.

Trim – A control valve trim refers to the internal parts that create a change in flow velocity and pressure energies – often referred to as the wetted surfaces, or parts (usually the plug seat, stem, and cage if present.) It is a fundamental component and materials should be chosen wisely. Some factors to consider are pressure, temperature, and fluid type.

Packing – Commonly a fibrous material or another compound (such as Teflon) that forms a seal between the internal parts of a valve and the outside where the stem extends through the body. It acts as a dynamic seal between the valve stem and the bonnet and must be properly compressed to prevent fluid loss and damage to the stem.

Actuator – Devices used to position the valves, they can be fully open, shut, or partial in any application that requires constant and precise control. May be a manually operated handwheel, manual lever, motor operated, solenoid operated, pneumatic operated, or by a hyrdaulic ram.