120:1 ratio, Pilot-to-close Check Valves Designed for Accumulator Circuits

Accumulator circuits have one thing in common. They need a means of discharging the energy stored in the accumulator so maintenance people don't get a rude surprise when they service the equipment. Circuits that use accumulators in parallel with pumps can use pilot-to-close check valves that discharge the energy to tank when the pump is shut down. Sun models CO*A do a good job with this.

Accumulator sense, pump unload circuits present a greater challenge. Some applications use pressure switches and solenoid  valves to unload the pump and some use hydraulic valves. Either way, the pump is unloaded to a small percentage of system pressure. The challenge is to keep the accumulator charged until the pump is actually turned off. See our previous highlight entitled Accumulator Sense, Pump Unload Valves.

A pressure switch based circuit could use a solenoid valve wired in parallel with the pump to discharge the accumulator. An all-hydraulic application calls for a specific valve. An application that charges the accumulator to 5000 psi (350 bar) and unloads the pump to 50 psi (4 bar) calls for a pilot-to-close check valve with a ratio in excess of 100:1.

Sun's COFO XD* cartridge has a ratio of 120:1. There is also an additional feature that you as a customer probably don't need to concern yourself with. Some pumps have very low leakage, and when shut off, would still maintain enough pressure to keep a 120:1  pilot-to-close valve closed. The COFO is designed to prevent this without sacrificing efficiency.