Process System Valve Types and What They Do

Process instrumentation valves are usually small connection-size components, often from about 1/8 inch to 1 inch. In a process system, the valve type determines whether the system is opening flow, shutting flow off, adjusting flow, preventing reverse flow, relieving pressure, bleeding pressure, or isolating an instrument line.

Common valve types in process systems include the following.

• Ball valves use a hollow rotating ball for quick quarter-turn flow control.
• Bonnet needle valves are used for fine, precise adjustment of fluid or gas flow.
• High performance actuated ball valves use an actuator to turn the valve stem and rotate the ball open or closed.
• Plug valves use a one-piece, top-entry design and are similar in layout to some top-entry ball valves.
• Toggle valves control flow with a directional toggle switch.
• Metering valves provide stable and accurate flow control in instrumentation, laboratory equipment, and analyzers.
• Check valves are one-way valves that help prevent backflow by allowing flow in the forward direction.
• Excess flow valves work like check valves, but include a spring-loaded shutoff that closes when flow exceeds a set closing rate.
• Relief valves help control system pressure by opening as pressure rises.
• Bleed valves shut off upstream pressure and bleed excess fluid or pressure from the system.
• Metering ball valves combine metering and shutoff functions in one valve body for gases or liquids.
• Manifold valves combine block or isolation valves for venting, isolation, and equalization in pressure measurement applications.
• Valve packing seals the space between the stem and bonnet to help prevent leakage.

The valve name is only one part of the selection. The connection size, port style, media, pressure, temperature, and sealing method still need to match the process system, especially when the valve is connected to instrumentation tubing or small process lines.