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Accumulator CircuitsCircuits shown here are limited to basic components. Such items as filters, speed control

valves, gauges, etc., are omitted for the sake of clarity. Each circuit shows a basic idea, and the features of more than one circuit can be combined, if desired, to get the desired results.

Accumulator Unloading. When the accumulator has been charged to adjustment setting on unloading valve V2, pilot pressure opens V2 and unloads the pump. When the systempressurehasdroppedabout20%,V2 closes and loads the pump. V2 is not a relief or by-pass valve; it is a special unloading valve with snap action characteristics.

This circuit is used for small pumps, up to 20 GPM. For larger pumps, one of thefollowing circuits may be used.

High Volume Unloading uses a relatively small accumulator unloading valve, V2, to vent the main relief valve, V1, which is a pilot-operated type of high flow capacity to suit the circuit. Accumulator unloading valves are not usually available in high flow capacities.

Electrical Unloading uses a pressure switch, PS, to load and unload the pump for charging the accumulator. This system may work out better with systems using solenoid valves in other parts of the circuit. Cut-in and cut-out pressures can be selected if the pressure switch has an adjustable differential.

Basic Accumulator Circuit. For circuits in which the oil flow is required intermittently, with relatively long resting periods between cycles. A low volume pump, PF, running continuously, can store high pressure oil in the accumulator, to be used in large volumes for short periods. Cylinder bore must be large enough so that sufficient force will be obtained even at the end of the required accumulator discharge, just before the pump is connected to recharge the accumulator. Recommendations on the preceding page may be followed to determine the total accumulator capacity needed for a given design. Recharging of the accumulator may take place at any part of the cycle – loading, curing, etc. Relief valve V1 is optional, but is recommended for extra safety.

Hi-Lo Circuit. The use of one large and one small accumulator is arranged to perform muchlikeaHi-Lopumpcircuit.Duringrestingperiods,bothaccumulatorsarechargedtofullsystem pressure. When V5 is shifted, oil from the large accumulator provides the necessary volume for rapidly advancing the cylinder, with oil trapped and held at full pressure in the small accumulator during this phase. When the limit switch is actuated, oil from the small accumulator is released by V2 to do the high pressure holding. This high pressure oil closes check valve V4, and the pump starts recharging the large accumulator during the holding cycle. At any time in the loading, pressing, or curing parts of the cycle that the accumulators become fully recharged, valve V1, which is an accumulator unloading valve, will unload the pump.

ACC.

PRESS.OUT

V3

PFV1 V2

ACC.

PRESS.

OUTV3

PFV1

V2

ACC.PS

PRESS.OUT

V3

V2

PFV1

V2

V3

ACC.

PF V4V2V1

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Fast closing of the cylinder is made possible using an accumulator kept charged by a relatively small volume, low pressure pump, PF1. When the cylinder bottoms out against the work load, PF2, a low volume, high pressure pump, takes over to build up high pressure in the cylinder while PF1 recharges the accumulator. V1 should be an accumulator unloading valve. During idle periods in the cycle, the very low volume of pump PF2 is allowed to discharge over relief valve V2.

Economical Circuit for Long Holding Cycles. Rapid traverse of the cylinder is done with combined oil from both pumps and the accumulator. When the cylinder stalls against the load, pump PF2 takes over and has sufficient flow to maintain full force from the cylinder, with the excess flow charging the accumulator through the restrictor, V4. During the cylinder holding time, pump PF1 is completely unloaded through valve V1, which may be any type of pilot-operated bypass valve. A variation of this circuit would be to omit PF1, V1, and V3 if high cylinder speed is not required.

Regeneration plus accumulator oil plus pump oil combine to give very rapid advance. Pump plus accumulator plus small rod area combine to give very rapid retraction. Circuit as shown is for high speed travel at low force, as no valving has been provided to get full force on the blind side of the piston at any time.

Forbestresultsusealarge-rod(2:1ratio)cylinder.ValvesV5 and V6 are pilot-operated check valves for connecting cylinder blind end either to tank or to rod end. V4 may be a 4-way valve of low capacity, as it handles oil only for the pilots of V5 and V6. Valve V2 is the conventional accumulator unloading valve to unload the pump when the accumulator becomes fully charged. This circuit works best in applications requiring high speed while the cylinder is in motion, but with a relatively long idle time between cycles to give the accumulator time to be recharged. Do not use this circuit on continuously reciprocating applications.

V2V1 V3

ACC.LARGE

PF

V4

ACC.SMALL

V6 V5

PF2PF1

V3 V4

V5

ACC.

V1 V1

PF2PF1

V3

V4 V5

ACC.

V6V2

V1

PF

V3

V4V6

V5

ACC.

V2V1