Double effect overcenter valves

Doubl effect overcenter valve-  doble effect versions are used to control the movement in both dierection. The single effect counterbalance valves are normally used to control the movement of an actuator in particular during the load lowering.

The valves consist of a body, made of aluminium (for pressures up to 275 bar) or steel (for pressure up to 350 bar), which contains a non-return valve a pressure relief valve and a pilot line.

They provide:

- Free flow in the direction from V to C, the oil flow opens the non-return valve;

- Maximum pressure control inside the actator, with distributor's spool connected to downstream in open center position;

Stop of the oil flow and thus support the load when distributor is brought back to a central position;

Block of the handling of the load when the pump is stopped (the movement of the spool from the neural position does not cause any downward movement of the load);

- The controlled lowering of the load is always proportional to the amount of oil sent into the other chamber of the actuator.

The valve is in fact opened only in the presence of a pilot pressure;

- Protection against pipes burst, if the valve is flanged directly to the actuator. 

Hydralic diagrams 

Pilot ratio - pilot pressure. The pilot ratio, typically > 1, is the ratio of the area subjected to the pilot pressure and the annlar area of load holding plunger. 

Formula

The valve allows oil flow fom C to V only when the force created by the load induced pressure on the plunger, added to the force acting on the pilot piston exceeds the spring load that acts in the opposite direction on the plunger.

Available example models:

          VBCD 3/8 DE-A   VBCD DE   VBCD DE A   VBCD DE A   VBCD DE FLV   VBCD DE FL   VBCD DE CC   VBCDF DE OMP-OMR