Valve Parts and Their Functions

II JAY SHRI KRISHNA II

Valve Parts and Their Functions

With reference of our previous blog on 'Valves Significance in Piping Field' - Valves are essential components in Piping Systems, and they play an essential role in controlling the flow of fluids (liquids or gases) through pipes.

In this blog on, Valve Parts and Their Functions we discuss the main parts of a typical valve used in Piping Systems:

The common Parts of Valves are, Body, Bonnet, Disc, Seat, Stem and Handwheel or Actuator as shown in the figure:

Valve Parts and Their Functions

Valve Body and Bonnet:

These are the main parts of the Valve, consist of the Valve Body and Bonnet.

Valve Body means the main outer shell or casing of the valve that contains and supports the internal components and Bonnet of Valve means the top part of the valve that covers and protects the internal components. It is usually bolted to the body. These two parts from the vessel or casing that holds the fluid going through the Valve.

A Bonnet is a cover on the Valve body. During Valve manufacturing, the internal parts are put into the body, bonnet is attached to hold everything together inside, as well as during maintenance purpose, to access internal parts of a Valve, a user can take off the bonnet. Some valves, like Plug Valves, lack bonnets altogether.

Valve bodies are made of usually Metallic, Brass, Bronze, cast/Ductile Iron, Steel, Alloy Steels & Stainless Steels which are very common. Plastic Valve bodies are used for relatively low pressure & temperature. PVC, PP, PVDF & Glass reinforced Nylon are common Plastic used for Valve bodies.

Valve Body Bolts and Nuts:

Fasteners that hold the body and bonnet together. They confirm a secure and leak-proof connection.

Ports:

Essential to the Valve body are the paths that allow flow into and out of the Valve which called Ports. These Ports are obstructed or opened up by the disc to control the fluid flow. Valves with two or three ports are the most commonly used, while Valves with multiple Ports are used in special applications.

Practically all Valves are built with some means of connection at the Ports. These includes Threads male or Female, NPT are most common. Compression Fittings, to suit tube/copper. Glue/cement application (especially for Plastics) nearly always a socket type connection, not a butt.

Flanges End Connections:

End connections that allow the valve to be attached to the Piping System. Flanges come with bolt holes for make safe the valve to the pipe flanges. Flanges are ANSI, BS, DIN or JIS (US, British, European, Japanese Standards) welding either Socket type or Butt Weld Type.

Trim:

The internal components of the valve that come into direct contact with the fluid. The trim includes parts like the valve disc, seat, and stem.

Valve Disc (or Plug):

The movable part that open, close, or partly obstructs the flow path within the valve called Disc. The disc in the Valve is movable so it can control the flow of fluid. Disc can come in various shapes, A round type of disc with fluid ways inside can rotated to direct flow between certain ports is called Ball. 

Ball Valves are valves which use spherical rotors, except for the interior fluid pathways. Plug Valves use cylinder-shaped or conically tapered rotors called Plugs.

Seat:

The Valve Seat is the inner surface in the body which contacts or could contact the disc to form a seal which should be leak-tight when the Valve is Shut. In other words, it is the sealing surface against which the valve disc makes contact when the valve is closed. It offers a tight seal to stop leakage. The seat remains static while a disc or rotor moves.

Depending on the Valve design, the Valve body & the Seat could come in one part of solid material, or Seat could be a separate part attached or fixed to the inside of the valve body.

There are two types of Seats: Soft Seat and Hard Seat

The Soft Seats are made of materials such as PTFE, or various elastomers such as NBR, EPDM. Every soft material is restricted by temperature. The benefit of Soft Seats is that they are more likely to offer 100% tight shutoff when valve is closed.

The hard Seats are made of metals and used for applications where there is heavy erosion due to the material flowing from the pipes is happen. These Valves have longer life. Therefore, metal seated Valves are ideal over Soft Seated Valves.

Gate Valve, Globe Valve, Check Valves are normally hard seated valves and Butterfly Valves, Ball Valves, Plug Valves, Diaphragm Valves are normally Soft Seated Valves.

Stem:

It is the rod that connects the valve disc to the actuator or hand-wheel. It transmits the indication from the actuator to the disc.

Spring:

Valves having Spring for Spring-loading, for shift the disc into some position by default but allow control to reposition the disc. For example, Relief Valves usually use a spring to keep the valve shut, but allow excessive pressure to force the valve open against the spring-loading.

Actuator:

Actuator is the mechanism responsible for moving the valve disc to control the flow. Actuators can be manual (hand-operated), motorized, pneumatic, or hydraulic.

Handwheel or Lever:

In manual valves, this is the hand-operated mechanism used to turn the stem and open or close the valve.

Packing:

A Packing is a sealing material used around the stem to prevent leakage along the stem. It provides a barrier between the fluid inside the valve and the external environment.

Gland:

Gland is the part that compresses the packing around the stem to create a tight seal. It is typically adjustable to control the tightness of the packing.

Yoke:

Yoke is a structure that supports the valve bonnet and stem. It helps in aligning the stem and provides stability to the valve.

Conclusion:

Valve Parts, including the body, bonnet, disc, and stem, collaborate to regulate fluid flow in various systems. The body houses the components, the bonnet secures them, the disc controls flow, and the stem facilitates movement. These components collectively ensure efficient and precise control of fluid in diverse applications.

All These parts can vary depending on the type of valve (e.g., Gate Valve, Ball Valve, Globe Valve & etc.) and its specific design and application in the Piping System. Different valves serve different purposes, such as isolation, throttling, or pressure regulation, and their internal components are designed accordingly.

Kindly, follow my all blogs and previous blog on

Piston Valve: Accurate in Fluid Control

Pinch Valve: Key to Effective Flow Management

Needle Valve: Excellent Accuracy in Fluid Control

Pipe Significance in Piping Field

Butt welded, Socket Welded & Flanged Fittings - Advantages and Disadvantages.

Section of Gasket Material Guide

Specialized Valves in Piping Systems

Valve Placement Guidelines in Piping

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