Hydraulic Power Supply with Accumulator

A more efficient supply system employing some additional components, is shown in Fig. 1. The additional components are: an accumulator, an off  loading valve and a non-return valve. On start up the bypass line is closed and, as the pump charges the accumulator, system pressure rises; when the pressure reaches a value corresponding to the high level setting of the off loading valve the bypass line is opened, thereby off-loading the pump. The accumulator now maintains system pressure with the non-return valve in its closed position. Since the flow required by the system has to be provided by the accumulator. The supply pressure will drop as the accumulator discharges. When the pressure reaches a value corresponding to the low level setting of the off-loading valve, the bypass line is blocked and the pump again supplies the system; the accumulator is re-charged and supply pressure rises. The sequence of operations is then repeated, the relief valve acting solely as a safety device and remaining seated under normal operating conditions.

This arrangement is particularly suitable for systems operating for extended periods under idling or low flow conditions. The rating of the pump and size of the accumulator depend on the duty cycle; therefore, if in addition to long idling periods the system is required to operate for extended periods at peak or near peak demand, the pump should be rated at
the maximum flow, enabling a small accumulator to be used to maintain supply under idling conditions. Energy dissipation and the consequent cooling problem is considerably reduced by using a power unit of this type rather than the simpler arrangement previously described.

Fig 1. Fix displacement pump with accumulator and off-loading valve.

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