Check Valves & Marine Valves

A check valve, also known as a non-return valve or one-way valve, is a mechanical device that allows fluid (liquid or gas) to flow in only one direction. Its primary purpose is to prevent backflow in a piping system.

How Check Valves Work

Check valves operate automatically based on the pressure of the fluid. They do not require an external handle, stem, or human intervention to function.

  • Forward Flow (Open): When the fluid pressure on the inlet side of the valve is greater than the pressure on the outlet side, it pushes open an internal closing mechanism (like a disc, ball, or flapper), allowing the fluid to flow through. The minimum pressure required to open the valve is called the "cracking pressure."
  • Reverse Flow (Closed): When the pressure on the outlet side becomes higher than the inlet pressure, or when the flow stops, the internal mechanism is forced back into its sealed position, preventing any fluid from flowing backward. This can be caused by gravity, back pressure, or a spring within the valve.

Common Types of Check Valves

There are several types of check valves, each designed for specific applications and flow conditions:

  • Swing Check Valve: This type has a hinged disc that swings open with forward flow and swings shut when the flow reverses. They are often used in systems with large-diameter pipes and low flow resistance.

  • Ball Check Valve: This valve uses a spherical ball as the closing mechanism. In forward flow, the fluid pressure pushes the ball off its seat. When flow stops or reverses, gravity or back pressure (and sometimes a spring) forces the ball back onto its seat to create a seal.

  • Lift Check Valve: Similar to a ball check valve, a lift check valve uses a disc or piston that lifts vertically off its seat to allow flow. It is guided to ensure proper alignment and is often used in high-pressure applications.

  • Spring-Loaded Check Valve: This type uses a spring to hold the closing mechanism (disc, poppet, or ball) against its seat. The fluid pressure must be strong enough to overcome the spring force to open the valve. The spring assists in a quick, non-slam closure.

  • Foot Valve: A specialized check valve installed at the bottom of a suction line in a pump or well. It has a strainer to filter out debris and prevents water from draining back out of the pump, helping to maintain "prime."