Learn 7 Most Important Parts of Valve

In this article, you will learn the different parts of valves. The valve is assembled product and consists of various parts. If you are working with valve, knowing of these parts is a must.

Valve Body

The valve body is the main pressure retaining part that also houses other valve parts, such as disk and seat. The valve body also provides passage for fluid to flow from the valve. The ends of the valve body connect with piping. These ends can be flanged, threaded and butt welding types that depend on the size and pressure of the piping system.

Valve bodies can be cast or forged in different materials, such as cast steel, stainless steel, and alloy steel, depending on the requirements.


Bonnet is the second pressure retaining part of the valve. It is also known as a cover. The bonnet connects with valve body by bolting, welding or threading to create valve enclosure.

In case of gate, globe, stop check, and diaphragm valves, it has an opening so that the valve stem can pass through it. Bonnet provides access to valve internals, during maintenance.

Usually, it contains a stuffing box and also a support yoke, and operating mechanism of the valve.


The disc is the part which allows throttles, or stops the flow, depending on its position. In the case of a plug or a ball valve, the disc is called a plug or a ball. A valve disc could be cast, forged, or fabricated. A disc is seated against the stationary valve seat or seats when the exception if check and safety-relief valves, in which the disc is moved away from its seat by fluid flow and pressure.


The seat is one of the main components that directly affect the leakage rate of the valve. A seat can be an integral part of the valve body or made of the forged ring or of non-metallic material.

A valve may have one or more seats. In the case of a globe and a swing-check valve, there is one seat, which forms a seal with the disc to stop the flow.

A gate valve has two seats. One on the upstream side and the other on the downstream side.

Multiport plug and ball valves may have several seats, depending on the number of ports in the plug or ball.


The stem is forged solid rod or shaft. The valve stem transfers the required motion to the disc, plug, or the ball for opening or closing the valve. It is connected to the valve handwheel, actuator, or the lever at one end and the valve disc on the other.

In gate or globe valves, linear motion of the disc open or close the valve, while in a plug, ball, and butterfly valves, the disc is rotated to open or close the valve.


The removable and replaceable valve internal parts that come in contact with the flow medium are collectively termed as valve trim.

These parts include valve seat, disc, glands, spacers, guides, bushings, and internal springs.

API standard has the standardized trim materials by assigning a unique number to each set of trim materials.


The actuator is a mechanism that operates the valve. It is connected to the stem and disk assembly. It may be manually operated by a handwheel, manual lever, gear, chain or it can be operated through the motor, solenoid, pneumatic, or hydraulic mechanism.