Valve

A valve is a mechanical device that controls the flow of a fluid (liquid or gas) through a pipe or duct. It can start, stop, throttle, or redirect flow, and it can also prevent backflow or relieve excess pressure.

Common types

• Gate valve: Opens by lifting a gate out of the flow path. Used for on/off service — fully open or fully closed. Not for throttling.
• Ball valve: Uses a rotating ball with a hole through it. Quarter-turn to open or close. Fast acting, reliable, and good for both on/off and throttling.
• Globe valve: Has a movable plug that seats against a stationary ring. Excellent for throttling — the flow path is S-shaped, giving fine control over flow rate.
• Check valve: Allows flow in one direction only. The disc or flap opens under forward pressure and closes when flow reverses. Used in pump discharge lines, water heaters, and irrigation systems.
• Pressure relief valve: Opens automatically when pressure exceeds a set limit, preventing over-pressurisation. Required on boilers, water heaters, and compressed-air systems.
• Butterfly valve: A disc rotates within the pipe bore. Compact and lightweight, used in large-diameter water and HVAC systems.
• Needle valve: Has a slender, tapered needle that seats into an orifice. Provides very precise flow control — used in instrumentation and hydraulic systems.

Materials

Valve bodies are made from brass (plumbing), cast iron (water mains), stainless steel (chemical and food processing), PVC (drain and irrigation), and exotic alloys (high-temperature or corrosive environments). The material must be compatible with the fluid and the operating conditions.