The check valve with cartridge style is crewed-in a cavity to achieve its function. The check valve below is two fluid way valve, A port (Inlet) and B(Outlet) port. The hydraulic fluid flows into A port until the pressure at A port is pressurized to push the poppet and the hydraulic oil flows in and squeezes out from B port then. The fluid from B port to A port is isolated by a steel ball or poppet (The sealed type depends on the valve function and working requirements.) The cartridge check valve is simple in inner structure and easily to installation and maintenance. –

Hydraulically Pilot Operated Check Valve Animation:
The hydraulically pilot operated check valve is open by hydraulic force to push the pilot spool. The fluid flow from P2 to P1 is isolated when there is no pressure in the chamber of K port, and the pilot spool in its normal position. When there is hydraulic oil in the K port and pressurized the pilot spool to move until opening the pressure unloading poppet, the port P2 connects to port P1 at the moment.
The hydraulically pilot operated check valve usually is used as a safe guard for lowering load or hydraulic actuators are locked hydraulically. –

Pilot Operated Check Valve Animation:
There are three ports of pilot operated check valve, the hydraulic oil at A port is through with B port when if there is a hydraulic oil at the A port and pressurize to push the valve poppet. Conversely, the fluid from B port to A port is blocked by the cone shape poppet firmly on its seat position. If there is a pilot oil to pilot port resulting in the spool to push the poppet always in a open position until no oil pressure in the pilot port. The pilot operated check valve/span> is mostly used in the hydraulic system where needs to keep the pressure for a certain time or hydraulic stable operation requirement. –