Pump-Relief Unload Circuit
The circuit shown in Fig. 15.3 contains ® a low pressure and large volume pump and © a high pressure and small volume pump. The circuit raises its efficiency by using ® and ©. In a case where the pressure in the circuit is lower than the pressure set at the unload valve, the output flow rate from ® and © are gathered and provided to the circuit. In contrast, in a case where pressure in the circuit is higher than the pressure set at the unload valve, the output flow rate from ® is by-passed to the reservoir by the unload valve, and the pressure is unloaded. In this case, pressure within the circuit is kept at a certain level by the output flow rate from © only. This circuit provides flow rate characteristics observed in a pressure vs. flow rate curve.
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