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Circuit idea: check-valve branch bypasses reservoir

Check-valve branch

I design auxiliary hydraulic systems for trucks. On many of these vehicles, there is not enough space for the optimum-size reservoir. In such cases, I use the circuit at right to accommodate the high flows generated by fixed-displacement pumps that are driven at maximum speeds.

Assume the pump delivers 50 Ipm at 800 rpm, and that space limitations dictate a 50-l reservoir. Return fluid passes through filter A to diffuser B in the tank. When the engine drivsi the pump at higher speed, the increased flow develops backpressure at orifice C. The orifice is sized to produce enough pressure force to crack open check valve D. Excess flow now passes through D directly to the pump's suction line. Note that the filter must be upstream from the branch circuit so that pressure drop through the filter does not affect the equation.