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Poppet Check Valves

It is important to note that the poppet style check valve is usually designed to be normally closed.  Poppet type valves generally utilise a spring to force shut the orifice by holding a component against a seal to replicate the backflow pressure.  Spherical shapes like ball bearings with smooth surfaces, which seal against an o-ring seal, or poppets, which generally incorporate an o-ring seal and seal against a smooth face.

When the forward pressure overcomes the spring force the valve opens, at this point the term cracking pressure is given to this action. An advantage of these types of check valve design are the low cracking pressures that can be achieved with repeatability. Small differentials in forward and backflow pressures can be accommodated.  Low cracking pressures such as 0.1psi are achievable. 

When the check valve is fully open, flow in one direction is relatively unrestricted. When closed the check valve should not exhibit any flow. The key benefit of building a spring into a check valve’s mechanism is that it largely eliminates the effect of gravity on check valve function. Without a spring, gravity and thus the valve’s vertical orientation can become a critical factor for a check valve to work properly.