Valves of all types are designed to work based on pressure on either side of the valve. For a check valve, the pressure on the inlet port of the valve is higher, forcing the liquid through the valve in one direction through the outlet port.
Should the pressure in the system on the inlet side of the valve drop, the ball, disc, diaphragm or another component in the check valve is pushed against that side of the valve, completely blocking the inlet so the liquid cannot flow back through the system. This is called the reseal pressure. It is the force required to push the ball, disc or diaphragm to prevent any flow.
With that in mind, each check valve is designed with a specific cracking pressure. This is the pressure upstream of the valve that is required to get the ball, disc, diaphragm or another component to move forward to allow the flow to occur through the valve. In some areas, the cracking pressure may be known as unseating pressure.
The Low Pressure Cracking Check Valve
While systems often run with thousands of pounds per square inch of pressure, it may be essential to use a low pressure cracking check valve in the system. This allows the release of the liquid through the system as the pressure builds, not requiring a full level of pressure before the flow starts.
These low pressure cracking check valve designs will be rated for a specific pounds per square inch or PSI level. This is not the same as the pressure that is required to provide a full opening of the check valve. It is important to remember these are two different measurements.
It is possible to have a low pressure cracking check valve made of metals, including brass, as well as plastics. Both can be a good option depending on the specifics of the system requirements.
