Check valves are among the simplest and most widely used valves in fluid power. They allow fluid to flow in one direction but not the other. They are used for control functions and zero-leak versions are widely used for load holding because of their simplicity and reliability. Adding to their versatility is that they come in conventional line mounted and cartridge versions.
Typical thread-in cartridge style check valves are large and mount to the surface of a manifold block. This surface mounting adds complexity and cost from the additional machining or drilling of internal passages required to integrate the valve into the circuit.
Isolation Check Valves
When used as a pressure-sensing isolation check valve, the need for zero leakage and flow rates greater than 4 lpm (1 gpm) are not needed. Standard check valves are available in a C8-2 or C10-2 cavity configurations, but these are large and costly, given the number that would be needed. Geometry of the cavity required can also restrict their placement within a manifold. The schematic shows an example circuit where isolation checks are used.
As with cast iron sectional valves, a common practice to reduce cost and save space was to drill the check valve seat into the manifold, then drop in a ball, spring, and port plug. Although simple in design and function, these types of check valves are not durable, as neither aluminum nor cast iron can hold up to the pressure cycles and flow impacting the ball onto the seat. Further complications arise for service due to the difficulty of changing out loose springs and balls in the field. If the check ball seat does become damaged, replacing the manifold is usually more economical than repairing it.
