Piston Valves
Piston valves are used in piping systems primarily for shutoff and regulation purposes, similar in function to globe valves. They offer reliable sealing and are often chosen for critical applications. The shutoff mechanism consists of a metal piston, two sealing rings made from durable materials, and a metal lantern bushing, providing a large sealing area compared to standard globe valves.
Types of Piston Valves
Piston valves come in two main varieties:
- Balanced Type – Suited for high-pressure applications.
- Unbalanced Type – Ideal for low-pressure conditions.
Key Components of Piston Valves
- Body: Typically cast construction, available with threaded, flanged, or welded ends, and designed to meet DIN standards. ANSI/BS standards may also be applied for end connections.
- Bonnet: Usually made from the same material as the body and fastened with bolts.
- Piston: Works with sealing rings to ensure proper isolation. The piston’s upper ring seals against the atmosphere, while the lower ring seals across the ports.
- Valve Rings: The sealing rings, made from high-quality elastomers or graphite, are essential for effective sealing.
- Lantern Bush: Serves as a spacer between the sealing rings.
- Spindle, Handwheel, and Gland Assembly: Ensure smooth operation and control of the valve.
- Yoke Bush: Connects the handwheel to the spindle for actuation.
- Packing: Ensures there are no leaks around the spindle.
Piston Valve Features
- Designs: Available in regulating (throttling) types, where the piston is tapered, and standard designs for shutoff purposes.
- Sealing Mechanism: Sealing rings expand under pressure to compensate for differential expansion, ensuring long-lasting operation.
- Stem Configurations: Options include inside screw rising stem and outside screw and yoke (OS&Y) designs for high-temperature applications.
These valves are often preferred for their durability and low maintenance requirements, with many operators referring to them as "install and forget" valves.