Check Valves

How Do Check Valves Work?

Check valves are pressure actuated -- the operating force comes from the fluid.
Some non-zero force is always needed to make a seal -- this can come from preloading the valve shut and/or also from fluid pressure in the reverse direction.
Preloaded valves are called "normally closed" and will always require some degree of non-zero, positive pressure in the forward direction to make them open.
Non-preloaded valve are called "normally open" and will begin to flow with the first application of pressure but may also leak in the reverse direction until sufficient reverse pressure is applied to make a seal.
All check valves have their flow curves specified with at least three pairs:
o an opening pressure defined as that needed for a specific small flow.
o a "full flow" at some higher pressure appropriate to the end application.
o a maximum reverse leakage at some pressure or over a pressure range.