Bladder Accumulator

Bladder accumulators combine the advantages of hydraulics and pneumatics. They are used to maintain pressure in a hydraulic system without requiring a pump to run. Bladder accumulators are part of the hydropneumatic hybrid systems.

Structure:

A spherical or cylindrical steel container houses a flexible and airtight bladder-shaped membrane, usually made of latex or rubber. This simple construction, consisting of a steel container and an inner membrane, makes the bladder accumulator a cost-effective component.

The internal rubber bladder must be replaced periodically before it becomes brittle and leaks. The trick to replacing the inner bladder is to fully evacuate it before installation. This makes it thin enough to be easily inserted into the steel tank.

Functionality:

The bladder is pressurized with a suitable filling gas. This process is also known as “pre-charging.” On the other side of the membrane, there is an interface to the hydraulic system.

If hydraulic oil is now forced into the bladder accumulator under high pressure, the gas in the bladder is further compressed. Since gases are highly compressible, a high back pressure can be generated, thereby storing the hydraulic pressure within the system.

A shut-off valve closes the hydraulic inlet until the hydraulic pressure is needed again. When the valve opens, the gas expands and pushes the hydraulic oil back into the system.

The bladder accumulator is a simple and energy-saving way to pressurize a system. However, it can only release its pressure once. To refill it with pressure or hydraulic oil, the oil must be pumped back into the bladder accumulator.

Applications

A common application for a bladder accumulator is in locking systems. They can be kept under pressure independently of a pump and lock when needed. While an external pump usually needs to be connected for unlocking, the locking function, for example, of a road barrier, can be maintained indefinitely.

Another application is found in aircraft. In medium-sized passenger aircraft, the landing gear is usually held in its bays under hydraulic pressure. This is a safety feature to ensure that the landing gear can always be extended. However, with the help of a bladder accumulator, a permanently running pressure pump in the hydraulic system becomes superfluous. Once retracted and secured with a locked bladder accumulator, the landing gear remains in position until the hydraulic system is relieved.

Bladder Accumulators in the Automotive Sector

The most famous example of bladder accumulators can be found in Citroen’s legendary DS car model. The legendary road holding, for which the car was so highly regarded, owes its secret to this technology. A bladder accumulator is installed in each wheel of a hydropneumatic suspension system. This simple yet very reliable technology is still frequently used today in high-quality vehicles.