Yuken Pilot Operated Check Valves
These check valves have a pilot piston, which works with remote pressure to open the closed check valve, allowing reversed flow. Two types, standard and decompression, are available. The decompression type has a main poppet valve combined with a decompression valve. When the pilot pressure increases to lift the pilot piston, the decompression poppet valve opens first, and then the main poppet after the pressure is reduced. These valves are used to moderate shock caused by a sudden pressure release, which often occurs during the return stroke of a press process. They maintain the actuator position and system pressure, opening/closing the seat; therefore, internal leakage can be kept at minimum.
When they are used with a restrictor or a counterbalance valve that produces back pressure on the outlet side of reversed free flow, a counter force may work on the piston, which opens/closes the poppet continuously and vibrates the valves as a result. If the valves are in such a hydraulic circuit, the external drain type should be used. Figure 4.13 shows the pilot operated check valve (CP*G- 06). Figure 4.14 shows the relationship between the minimum pilot pressures and the pressure at the inlet side of reversed free flow. Figure 4.15 shows the pressure drop characteristics in the free flow and in the reversed flow.
Figure 4.16 shows circuit examples of the internal and external drain types. When the outlet side P1 is directly connected to the tank in reversed free flow (a), the internal drain type is normally used. When back pressure is applied to the outlet side P1 (b), the external drain type should be used.
Categories: Directional Control Valves | Leave a comment