Hydraulic accumulators store hydraulic fluid under pressure to supplement pump flow and reduce pump capacity requirements, maintain pressure and minimize pressure fluctuations in closed systems absorb shocks, and provide auxiliary hydraulic power in an emergency. Here’s how.

The Basics

A hydraulic accumulator is a pressure vessel containing a membrane or piston that confines and compresses an inert gas (typically nitrogen). Hydraulic fluid is held on other side of the membrane. An accumulator in a hydraulic device stores hydraulic energy much like a car battery stores electrical energy.

Its initial gas pressure is called the “precharge pressure.” When the system pressure exceeds the precharge pressure, the nitrogen gas is squeezed, compresses and decreases in volume, letting hydraulic fluid into the accumulator. The accumulator’s fluid volume increases until the system reaches its maximum pressure (P2). When system pressure decreases, the nitrogen gas expands and forces the fluid out of the accumulator, providing power to the hydraulic system, until the system and accumulator pressures equalize (P1).

Properly used accumulators increase hydraulic system performance and efficiency, lower operating and maintenance costs, provide fail-safe protection and extend system life by minimizing failure of pumps, pipes and other components.

Its initial gas pressure is called the “precharge pressure.” When the system pressure exceeds the precharge pressure, the nitrogen gas is squeezed, compresses and decreases in volume, letting hydraulic fluid into the accumulator. The accumulator’s fluid volume increases until the system reaches its maximum pressure (P2). When system pressure decreases, the nitrogen gas expands and forces the fluid out of the accumulator, providing power to the hydraulic system, until the system and accumulator pressures equalize (P1).

Properly used accumulators increase hydraulic system performance and efficiency, lower operating and maintenance costs, provide fail-safe protection and extend system life by minimizing failure of pumps, pipes and other components.

What Accumulators Do
Here are the top reasons for using accumulators:

To supplement pump flow. The most common use for accumulators is to supplement pump flow. Some hydraulic circuits need high-volume flow, but only for a short periods, and then use little or no fluid for an extended period. When half or more of the machine cycle does not use pump flow, designers usually install an accumulator circuit.

Accumulators need a pressure drop to operate. In some cases, the final design calls for a higher pressure than initially planned. For example, in the circuit shown above, it takes at least 2,000 psi to perform the work, but the accumulators must be filled to a higher pressure so they can supply extra fluid without dropping below the system’s minimum pressure. So, this circuit uses 3,000-psi maximum pressure to store enough fluid to cycle the cylinder in the allotted time and still have enough force to do the work.

The circuit uses several accumulators to supplement pump flow because the dwell time is 45 sec. out of the 57.5-sec. cycle. Its 22-gpm fixed-volume pump operates on pressure during most of the cycle to fill the cylinder and accumulators. Without the accumulators, this circuit would require a 100-gpm pump driven by a 125-hp motor. Although the initial cost for a smaller pump and motor plus the accumulators may be close to that of the larger pump and motor, energy savings over the machine’s life makes this accumulator circuit more economical.

Read more: Back to Basics: Accumulators