Alternative Circuit for Power Supply
Accumulator and Variable Displacement Pressure Compensated Pump

Graphical
Representation:

Circuit Application:

Most hydraulic accumulators are used in one of four types of circuits mentioned below:

1. Supplement pump flow in circuits with medium to long delays between cycles.
2. Hold pressure in a cylinder while the pump is unloading or stopped.
3. Have a ready supply of pressurized fluid in case of power failure.
4. Reduce shock in high velocity flow lines or at the outlet of pulsating piston pumps.

Circuit Description:

A pressure compensated pump maintains pressure while flow changes to meet the needs of the circuit. When the first actuator in the system starts to move, there is no flow for it until pressure drops. As pressure drops a pressure compensated pump will go on stroke quickly but there will be a slight pause before flow actually starts. With the addition of a small accumulator nearly eliminates startup pause. This enhances system response while reducing cycle time and pressure fluctuations. When the pressure reaches compensator setting, the pump starts to shift to no flow. All pump flow during the shifting time has no place to go, so this excess flow makes a pressure spike of 5-10 times the compensator setting. This pressure spike can cause premature failure of the pump, plumbing and actuators. An accumulator will take in this small volume of oil with a minimal spike.

Cost Notes:

1. The cost of the accumulators usually offset savings on these smaller components, but down sizing saves on operating costs.
2. This accumulator circuit maintains pressure in the cylinder while unloading the pump. It also conserves energy while using an inexpensive fixed volume pump.

Safety Notes:

1. As with any accumulator installation, safety is important. When shutting a circuit down for maintenance, always drain the accumulator.
2. A manual drain valve works, but the automatic drain (with pilot check valve) is better.
3. When the pump starts and as long as it is running, a pilot to close check valve blocks the drain port. Other check valve isolates the pump from accumulator back flow when it stops or fails.
4. There is no electrical wiring needed, so the accumulator dump valve is invisible to the control circuitry.
5. For a safe accumulator circuit, a means to discharge stored energy at shut down is necessary.
6. CAUTION! ALWAYS CHECK AN ACCUMULATOR CIRCUIT FOR PRESSURE BEFORE WORKING ON IT. NEVER ASSUME THE AUTOMATIC UNLOADING WORKED!!!!

Note: for more information see [Reference].