Why Use an Accumulator?

Wikipedia defines a hydraulic accumulator as "a pressure storage reservoir in which a non-compressible hydraulic fluid is held under pressure by an external source. The external source can be a spring, a raised weight, or a compressed gas." That seems straightforward enough but, "why use an accumulator"?

Thermal Expansion Compensation

When closed loop hydraulic systems are subjected to heat conditions, both the pipelines and hydraulic fluid expand volumetrically. And, since the coefficient of cubical expansion of most liquids is higher than the pipe materials, the expanded liquid volume increases the entire system pressure. This condition may cause pressure to exceed the limits of safety – or inflict damage to sensitive and expensive system components. Under these conditions, the installation of an accumulator of the proper capacity, pre-charged to the normal system working pressure, takes up any increase in the system fluid volume, thus maintaining the system pressure within a safe operating range. The accumulator also feeds fluid back into the system as thermal contraction takes place.

Hydraulic Fluid Holding Device

In some hydraulic systems, it is necessary to maintain high pressure in a cylinder for long periods of time. An accumulator can be used very effectively in these systems by providing a reservoir of hydraulic fluid that helps maintain pressure levels and eliminate pressure variations created by varying demands of different branches of the system. There are additional benefits including reduced wear on the pump and motor (adding to the life of the overall system) and reducing the possibility of the hydraulic fluid overheating (helping to prevent catastrophic failure and improving worker safety).

Auxiliary Power Source

The most common application of a hydraulic accumulator is as an auxiliary power source. For this application, an accumulator stores the hydraulic fluid provided by a pump during a portion of the work cycle and then releases the stored fluid to complete the cycle. The advantages of this are obvious, especially in reduction of power used (cost reduction) and wear and tear on the motor and pump in a system (increased component life). In a hydraulic system where intermittent operations are being performed, the use of an accumulator can allow an appropriate reduction in the size and typically the cost of the hydraulic power unit.

Leakage Compensation

In most hydraulic systems that are pressurized for long periods of time when idle, the pressure will slowly reduce through internal or external leakage (indeed, some systems are deliberately built to allow this). With the correct instrumentation and accumulators, the pressure can be automatically re-established once it drops below a certain minimum. An accumulator in this application saves electricity, helps control overheating and wear and tear on other system components.

Emergency Power Source

Some hydraulic systems require the automatic repositioning of key components for safety reasons whenever there is a power outage. Appropriately sized and positioned hydraulic accumulators can provide the power source necessary to move these components to their safe positions whenever the system's instrumentation detects a power failure. Again, the benefits of this capability are obvious in the improved safety and reduced cost by reducing inappropriate wear and tear on key system components.