Piston accumulator: pressure provision without power

The piston accumulator is a hydropneumatic component in hydraulic systems. It is used to provide pressure on demand without requiring an electrically driven pump. The piston accumulator can therefore be used for emergency operation functions, to save energy, and for many other functions.

Piston accumulator: design and function

The piston accumulator is a hydropneumatic element, similar to the bladder accumulator or the diaphragm accumulator. It consists of a gas chamber and an oil chamber. The two chambers are separated by a tightly sealing but movable piston. Unlike in an engine or a compressor, however, the piston has only a separating function. It does not transmit force; instead, it moves freely between the media.

The piston accumulator is “charged” by applying high pressure on the hydraulic side. The piston compresses the gas on the opposite side. This process is also referred to as “pre-charging the gas”. The piston is then locked in place. When the gas pressure is needed, the lock is released and the pre-charged gas transfers its pressure to the hydraulic system. The piston then moves toward the oil side until the gas has expanded or the piston has reached its end position.

Differences between the piston accumulator and the diaphragm or bladder accumulator

The spherical diaphragm accumulator is used less for storing pressure and more for damping pressure fluctuations. The best-known application of the diaphragm accumulator is in the hydropneumatic suspension of larger Citroën cars.

The also spherical bladder accumulator offers an optimal ratio of space requirement to performance. It is used wherever a high emergency pressure is to be provided with minimal space requirements.

In terms of the space-to-performance ratio, the piston accumulator is not as good as the bladder accumulator. However, it can be integrated more effectively into existing installation spaces. Instead of a spherical pressure vessel, the piston accumulator has a cylindrical design. Its length and diameter, as well as the number of units, can be selected so that it fits optimally into the available space.

Applications of piston accumulators

The piston accumulator can be used for many applications. Typical examples include emergency opening or emergency closing of heavy flaps, doors, hatches, or bulkheads. In the meantime, however, the piston accumulator has become established in the design of construction machinery such as dump trucks and, in particular, excavators and material handlers. In these applications, it serves as an effective component for reducing energy costs. The function is as follows:

The load of a payload lifted to a high level (e.g., demolition of buildings, removal of higher-stacked containers, filling bulk material into dump bodies, etc.) compresses a hydraulic cylinder by gravity. The pressure is routed to the piston accumulator. There, the gas is pre-charged and held until it is released again. When lifting an empty bucket or tipping a dump body, the additional force from the piston accumulator is then available. Lifting the unloaded attachment is then significantly more energy-efficient than without a piston accumulator.

Material handlers with lifting systems in which this hydropneumatic hybrid technology is used are standard, for example, on larger material handlers from SENNEBOGEN. LIEBHERR offers construction machinery that provides hydropneumatic support for the slewing motion of the uppercarriage. However, the costs for this hydropneumatic upgrade are very high. It is therefore only used on construction equipment of a corresponding size.