Parts of a valve

A valve comprises of the following parts: a body, a bonnet, a trim, an actuator and packing.

1. The body

The body is the outer casing of the valve; it contains all internal parts (also known as trim). Commonly known as shell, Valve bodies are made of Steel and Plastic. Valve made in Brass, Bronze, Gunmetal, Cast Iron, Steel, Alloy Steel and Stainless Steel is used across various industries. The valve body is manufactured with nozzles that are threaded, flanged, butt-welded or socket-welded, to fit on diverse piping systems.

2. Bonnet

The bonnet acts like the cover or lid of the body, it is connected to a valve by a joint that is either threaded or welded or bolted. Therefore, a bonnet is removed to access the core of the valve, either for maintenance or replacement. The bonnet and the body, both, are responsible to hold all iparts within. The weld joints or bolts, connecting the bonnet to the body, are pressure-retaining parts. Some valves like plug and ball valves do not have bonnets. Bonnets may leak; they vary in size and determine a share the cost of valve production.

3. Trim

The interior components of the valve collectively form a trim, consisting of a disc, seat, stem and sleeve. A trim facilitated the flow of the fluid and other motions and controls inside a valve.

The disc allows, restricts, stops and controls the flow of media according to its positioning. It can either move linear inside a valve or rotate around a stem or hinge. Being a pressure related piece, discs are hard surfaced making them durable.

The seat rests at the bottom of the valve and is a seating surface, when it comes in contact with the disc it forms a seal, leak proof. There are hard-seated valves, made of metal and soft-seated valves, made of softer materials. Hard-seated valves are sturdy while soft-seated valves leak less.

The stem conveys motion from the handle to the disc, passing through a bonnet. The motion conveyed can be a linear force or a rotational torque and a packing is used to keep the stem and the bonnet fastened.

The union between the disc and the seat and the positioning of the disk to the seat dictate the valve’s functioning.

4. Actuator

An actuator is an external handle, it controls the valve. Some valves may not have an actuator, some valves are automatic i.e. they are self-controlling with no actuators required to control them.

5. Packaging

The packaging is made up of a stem and a bonnet with a gasket in between, to promote a tight seal. The packaging must be accurate, either to avoid injury to the stem or gas/liquid leak.

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