Hydropneumatic Suspension – The Best of Two Worlds

Hydraulics and pneumatics share the ability to absorb forces via media. Hydraulics are characterized by the safe handling of particularly high pressures. Pneumatics are known for gently cushioning high forces. In combination, both technical approaches offer a solution for moving heavy loads weighing tons smoothly and gently, while protecting materials. In mechanical engineering, this leads to various approaches for cost-effective and highly efficient solutions, such as hydropneumatic suspensions.

The Basic Principle of Hydropneumatic Suspension

Hydropneumatic suspensions consist of the following components:

• pneumatic accumulator
• diaphragm
• connected hydraulics.

The accumulator is a gas-filled container. It is under high pressure or is “pre-stressed,” as it is called in technical jargon. No matter how high the gas pressure, as long as it is in a gaseous state, it can be further compressed. This is the essential difference from the liquid in a hydraulic system.

The diaphragm in the accumulator separates the gas side from the oil side. The hydraulic pressure is transmitted to the gas chamber via the diaphragm. For this reason, pneumatic accumulators are usually spherical or cylindrical. The circular cross-section makes the production of rubber diaphragms particularly easy and optimally absorbs forces.

Designed as a suspension, the accumulator’s task is to absorb and cushion pressure peaks occurring as shocks and impacts. The result is a particularly smooth and material-friendly dissipation of irregular forces.

Other Uses of Hydropneumatics Besides Hydropneumatic Suspension

In addition to being used as a suspension, hydropneumatics are employed in many other applications. Typical uses of this technical principle include:

• Accumulators for emergency operations
• Hybrid cylinders

An accumulator can store a certain amount of residual energy. This can be used in the event of a hydraulic pump failure to move the machine into a safe state. They are also often used for the emergency opening or closing of flaps and doors.

Hybrid cylinders are very popular in construction machinery, especially demolition excavators. They use the weight of the lifted load to pre-stress the accumulator. The energy gained in this way is used to lift the empty boom. Excavators with hybrid cylinders thus operate very efficiently and fuel-efficiently.