Hydraulic Accumulators

What is a hydraulic accumulator?

A hydraulic accumulator is a pressure storage device that stores hydraulic energy by compressing a gas, usually nitrogen, or using a spring or weight. It releases that stored energy back into the system whenever extra flow or pressure is needed, helping systems run more efficiently and safely.

In practical terms, an accumulator acts like a rechargeable battery for your hydraulic system. During quiet periods it quietly stores energy; during peak demand it delivers that energy back on tap. This means a smaller pump can handle short bursts of high flow, pressure stays stable as loads change, and sudden shocks are absorbed before they can damage pumps, valves and pipework.

Because they store and release energy on demand, hydraulic accumulators also provide a vital safety function: they can supply emergency hydraulic power to close valves, operate brakes or complete a shutdown sequence if the pump or power supply fails. That combination of efficiency, stability and safety is why hydraulic accumulators appear in almost every industry that relies on hydraulics.

How does a hydraulic accumulator work?

A hydraulic accumulator works on a simple principle: liquids are nearly incompressible, while gases compress easily. Pressurised oil compresses the nitrogen gas inside the accumulator to store energy. When the system needs more flow or pressure, the gas expands and pushes the oil back out.

The accumulator is pre-charged with nitrogen to a set pressure before it's connected to the hydraulic circuit. Once in service, it moves through two repeating phases, charging and discharging, as system demand rises and falls.

Charging phase

• The hydraulic pump accumulator delivers pressurised oil into the accumulator.
• The oil compresses the nitrogen gas inside the unit.
• The compressed gas stores potential energy, ready for use.

Discharging phase

• When the system demands more flow or pressure, the compressed nitrogen expands.
• It pushes the stored hydraulic oil back into the system.
• The released energy supplements the pump during periods of high demand.

What are the types of hydraulic accumulators?

The three main types of hydraulic accumulators are bladder, piston and diaphragm accumulators. Each uses nitrogen gas to store energy but differs in pressure range, response speed and size. HFT also supplies hydraulic dampers, accumulator charging kits and a full range of accessories.

Choosing the right type comes down to your pressure range, the volume of energy you need to store, how quickly the accumulator must respond, and the space you have available.

Bladder accumulators

Hydro-pneumatic bladder accumulators use a flexible, nitrogen-filled bladder inside a steel pressure vessel. The bladder keeps the gas and oil completely separated and responds almost instantly to pressure changes, which makes bladder accumulators the go-to choice for shock absorption, pulsation damping and surge protection. HFT stocks 16 bladder accumulators across a range of sizes and pressures.

Piston accumulators

Piston accumulators use a sliding piston to separate the gas and oil, allowing them to handle large volumes and high pressures across a wide temperature range. They're ideal for energy storage, dampening and surge alleviation in demanding, high-duty applications. HFT stocks a selection of 7 piston accumulators.

Diaphragm accumulators

Compact diaphragm accumulators use a flexible diaphragm to separate gas and oil in a small, lightweight body. They respond well to small pressure changes and suit systems that mainly need pressure maintenance in a limited space. HFT stocks a selection of 6 diaphragm accumulators.

Dampers, charging kits and accessories

Alongside accumulators, HFT supplies hydraulic dampers to simplify storage and extend versatility, Olaer and Hydac accumulator charging kits for correct nitrogen pre-charge and maintenance, and a full range of accessories for isolating and unloading functions.

What are hydraulic accumulators used for?

Hydraulic accumulators are used to store energy, maintain system pressure, absorb shocks, dampen pulsations and provide emergency power. They're especially valuable in systems with fluctuating flow demands, high-pressure operations or safety-critical functions, from hydraulic presses and mining equipment to offshore blowout preventers.

What are the benefits of a hydraulic accumulator?

Hydraulic accumulators improve energy efficiency, stabilise pressure, absorb shock and provide emergency power. By storing energy for peak demand, they let you use smaller pumps, reduce pump wear, cut noise and vibration, and lower total running costs – while improving system reliability and productivity.

• Energy storage & efficiency: store energy under pressure and release it on demand, so smaller pumps can meet peak flow and cut energy use.
• Pressure stabilisation: hold consistent pressure despite changing loads for smoother, more consistent performance.
• Shock & pulsation damping: absorb hydraulic shock (water hammer) and smooth pump pulsations, protecting pumps, valves and pipelines.
• Emergency power: supply stored energy to operate critical equipment safely during power or pump failure.
• Reduced pump wear: less frequent cycling and peak loading extends pump life and lowers maintenance.
• Lower lifecycle cost: smaller equipment, less downtime and reduced energy use lower total cost of ownership.

Do hydraulic accumulators need to be tested by law?

Yes. Under South Africa's Occupational Health and Safety Act and Mine Health and Safety Act, hydraulic accumulators must be conformity-assessed, pressure-tested and certified every 36 months – whether made locally or imported. HFT's accumulator certification centre can test, certify and repair units up to 50 litres.

This is a legal requirement, not just best practice. Because accumulators store energy under high pressure, a failed or uncertified vessel is a serious safety risk to people and equipment. Regular testing keeps your operation compliant and your team safe.

At our facility, every accumulator undergoes an internal and external inspection and a hydrostatic pressure test. Units tested at HFT also receive safety instructions covering mounting, commissioning and maintenance, plus original manufacturing records that owners must keep for the lifetime of the vessel.

Not sure if your accumulator is due? Use this quick compliance check:

• Has it been more than 36 months since your last certification?
• Was the accumulator imported without a local conformity assessment?
• Are you missing the original manufacturing records or safety documentation?
• Has the unit been repaired, moved or recommissioned since its last test?

If you answered "yes" to any of these, your hydraulic accumulator may be due for testing. Our new, state-of-the-art test bench makes HFT one of the few facilities in Africa able to certify accumulators up to 50 litres.

Why choose hydraulic accumulators from Bosch Rexroth and HFT?

Choose HFT for genuine Bosch Rexroth and Olaer accumulators backed by Africa's largest hydraulics and automation range, local stock, expert technical support and an on-site certification centre. We help extend your system's lifespan, reduce downtime risk and keep your operation compliant and reliable.

• Genuine Bosch Rexroth and Olaer products, trusted worldwide.
• Large selection of local stock – 16 bladder, 7 piston and 6 diaphragm accumulators, plus dampers, charging kits and accessories.
• On-site certification centre and test bench for units up to 50 litres.
• Expert engineering support to size, specify and maintain your system.
• Continent-wide supply and support from Africa's hydraulics leader.

Explore our range of hydraulic accumulators!

Ready to find the right hydraulic accumulator for your application? Call 011 976 7300 or fill in the Contact us form.