A piston valve is a type of linear motion valve that uses a piston or plunger to control the flow of fluids through a cylindrical passage. The piston moves axially within the valve body to open, close, or throttle the flow passage, allowing for precise control of fluid flow. Here's how a piston valve works:

1. Construction:

   • A piston valve typically consists of a cylindrical valve body with an internal passage and two or more ports for fluid inlet and outlet.
   • Inside the valve body, a piston or plunger is fitted with a sealing element, such as a rubber or elastomeric seal, to provide a tight shut-off when the valve is closed.
   • The piston is connected to an actuator, such as a handwheel, pneumatic cylinder, or electric motor, which provides the force necessary to move the piston within the valve body.

2. Operation:

   • When the piston valve is in the closed position, the piston seals against the valve seat to prevent fluid flow through the passage.
   • To open the valve, the actuator applies force to the piston, causing it to move axially away from the valve seat and open the flow passage.
   • As the piston moves, fluid flows through the valve body from the inlet port to the outlet port, allowing for the desired flow rate.
   • To close the valve, the actuator reverses the direction of the piston, pushing it back towards the valve seat to seal off the flow passage and stop fluid flow.

3. Features:

   • Piston valves offer several advantages, including tight shut-off, precise control, and high-pressure capabilities.
   • They are suitable for applications requiring accurate throttling control, such as steam, gas, and liquid services in industrial processes.
   • Piston valves are available in various configurations, including straight-through, angle, and Y-pattern designs, to accommodate different piping layouts and installation requirements.
   • They are commonly used in industries such as power generation, oil and gas, chemical processing, water treatment, and steam distribution.

4. Applications:

   • Piston valves are used in a wide range of applications, including:
     • Steam and condensate systems
     • Boiler feedwater control
     • Process control and regulation
     • High-pressure hydraulic systems
     • Cryogenic applications
     • Severe service conditions requiring tight shut-off and reliability.

In summary, a piston valve operates by using a piston or plunger to control the flow of fluids through a cylindrical passage within the valve body. By moving the piston axially, the valve can open, close, or modulate the flow passage to achieve precise control and tight shut-off in various industrial applications.