How Accumulators Work in Hydraulic Systems

Have you ever wondered how an accumulator works in a hydraulic system? Hydraulic accumulators are essential to store and power energy to better assist systems in performing hydraulic activities. In this article, you will learn what accumulators are, the types of accumulators, how they work, their uses, and their advantages. By the end of the article, you will understand how accumulators work and why they are useful in hydraulic systems.

What Is a Hydraulic Accumulator?

Hydraulic accumulator is defined as a component of hydraulic systems responsible for energy storage and is usually under pressure. It is just a closed chamber filled with an incompressible hydraulic fluid and a compressible gas, for example, nitrogen, and divided by a flexible bladder or a piston. The gas is present in the system and is pre-charged to a set pressure.

When a hydraulic pump makes more fluid than required by the system then the accumulator stores this excess energy by allowing the fluid to enter under high pressure to compress the gas. When the system needs more flow rate than the pump can deliver, then the compressed gas forces the stored fluid to the system from the accumulator. Thus, the accumulator plays the role of a standby energy source that regulates the required pressure in the system.

Types of Hydraulic Accumulators

There are three main types of hydraulic accumulators, each using a different method to separate the gas charge from the hydraulic fluid:

Bladder Accumulators

The two general types are bladder accumulators and hose accumulators. They come with an expandable, inflatable type balloon rubber called bladder enclosed within a metal casing. The compressed gas is stored inside the bladder while the space between the bladder and the shell is filled with the fluid. When the gas is compressed, the bladder is squeezed at the same time that the fluid enters. Bladder accumulators offer high flow discharge rates and can serve mid to high pressure systems well.

Piston Accumulators

A piston accumulator consists of a cylinder in which one end is occupied by gas while the other end is occupied by fluid and separated by a sliding piston that is provided with gaskets or O-rings. On the gas side, the piston is usually pre-loaded with a spring. The piston type of accumulator can, therefore, accommodate very high pressures and large volumes of fluids. They are generally employed in operations that are highly demanding in terms of performance and that require significant force. The first limitation is that these seals may wear out after some time of use due to the sliding motion that they undergo.

Diaphragm Accumulators

Diaphragm accumulators employ a flexible disc or diaphragm that separates the fluid from the gas. The diaphragm is shaped to match the shape of the shell. This design is also small in size and potentially less expensive. Diaphragm accumulators are the simplest to design, but they come with less fluid capacity and lower pressure ratings compared to bladder and piston accumulating types. They are most suitable where the use of pressure is low to medium, and the amount of liquid being pushed through the system is also low.

How Does an Accumulator Work?

Now that we’ve covered the types of accumulators let’s look deeper into accumulator how does it work:

The accumulator is initially pressurized with an inert gas to a pressure less than the hydraulic system’s minimum working pressure. This gas charge is what makes it possible for the accumulator to store energy.
When the hydraulic pump turns it consequently creates flow as well as pressure. When the system pressure rises higher than the gas pre-charge, the fluid begins to enter the accumulator.
When hydraulic fluid is pumped into the accumulator, the pressure in the enclosed gas charge also rises. The said gas works as a spring system that opposes the forces exerted by the fluid in this case. The accumulator’ charges up’ and stores energy in this compressed gas.
If the rate of flow demanded by the system is more than the supply rate provided by the pump or if the pump has stopped, the compressed gas forces the stored fluid out of the accumulator.
This fluid rises into the system and can sustain pressure and operation until the pump comes back online or until the accumulator runs empty. The accumulator’ releases’ the energy that is accumulated.
When again there is demand for the system and pump flow is greater than what is required, the accumulator recharges and the cycle begins again.

An accumulator charges and discharges at a certain rate due to the size of the fluid ports, pressure differential, the type and pre-charge of the gas, and viscosity of the fluid. Bladder and diaphragm accumulators respond faster than piston types due to low inertia.

Applications of Hydraulic Accumulators

So, what exactly do accumulators do in hydraulic systems? Their energy storage ability lends itself to many applications:

Relaying of pump flow during a particular period of the day or week when demand is high
Sustaining system pressure during fluctuations in the pump’s efficiency
To supply power in the case of an emergency when pump failure happens
It tends to absorb pressure spikes and pulsations in order to work freely and with lesser pressure.
Minimizing the pump sizes with the help of controlling intermittent flow condition
Accommodating for leakage and thermal expansion in fluids
Powering auxiliary functions like hydraulic cylinder return

In fact, any hydraulic system that has varying flow or pressure demand stands to gain from the use of an accumulator. Such systems are widely used in industrial presses, machine tools, mobile equipment, aircraft control systems, and many others.

Benefits of Using Accumulators in Hydraulic Systems

Incorporating accumulators into a hydraulic system design offers several key advantages:

Increased efficiency – accumulation of loads means that small pumps and motors can be utilized, which in turn reduces power usage. The pump also does not have to run at one constant speed and can be operated in start-stop cycles.
Smoother operation – By absorbing pulsations and pressure spikes, accumulators provide a more consistent system pressure and reduce vibrations. This results in a smooth and easier motion with greatly enhanced control of the force applied.
Faster response – The accumulator is capable of delivering a high flow rate immediately, and this response time is much better than with the use of a pump only. This is valuable in emergency situations.
Longer component life – Decreasing pressure spikes and vibrations with an accumulator lowers stress on all sorts of pumps, valves, hoses, and actuators. Seals and other wear components last longer.
Compact design – The utilization of accumulators means that smaller lines, valves, and other equipment can be used for carrying peak flow. It can also make the overall hydraulic system more compact.
Lower cost – Smaller volume pumps, motors, and other components can be incorporated. Pump operation in cycles is beneficial since it consumes less power. Maintenance is decreasing because the life of components is increased. This altogether reduces the overall cost of the hydraulic system.

When properly applied and maintained, accumulators are useful as an enhancement to many hydraulic systems with increased performance and reliability.

Frequently Asked Questions (FAQ)

How do I select the right type of accumulator for my system?

Some of the factors that need to be taken into account while selecting an accumulator include operating pressure range, volume and flow rate of the fluid, cycling frequency and response time, compatibility of the operating fluid, the range of temperature, and the size and mounting considerations. Bladder types are appropriate for most industrial operations, piston types are ideal for charge/pressure requirements, and diaphragm types are economical and small for low pressure. For best operating and durability characteristics, it is advisable to contact the hydraulic system manufacturer or accumulator manufacturer to assist in the selection and sizing of an accumulator for a specific application.

What maintenance is required for hydraulic accumulators?

Hydraulic accumulators are generally low on maintenance, but they must be checked and serviced from time to time to ensure that they function safely and effectively. Among the regular maintenance, the monitoring of the gas pre-charge pressure is crucial, as it is done every 6-12 months with a charging kit and adjusted accordingly. Consequently, an improper pre-charge condition may result in issues such as bladder extrusion or poor performance. It is also important to check the accumulator for leakage of gas or fluid. Also, damaged seals or O-rings should be replaced as soon as possible. In regard to bladder-type accumulators, it is advised that the bladder be replaced every five to ten years so as to avoid situations where the bladder gets ruptured, allowing the gas and fluid to mix.

Can accumulators be used in both hydraulic and pneumatic systems?

Although primarily used in hydraulics applications, some pneumatic systems may use accumulators to store the pressurized air for use in maintaining pressure, for actuation, or for cleaning purposes. However, pneumatic accumulators are much larger and have lower pressure than hydraulic ones because of the compressibility of air. Consequently, although it is possible to apply accumulators in certain pneumatic applications, it is considerably less typical than in hydraulic platforms where pressures are higher and fluids’ compressibility is lower, causing accumulators to be highly efficient. The selection of the accumulators must be made with respect to the application requirements and conditions in which the components will operate.

In Conclusion

Hydraulic accumulators are one of the key components of the majority of fluid power systems because of their ability to store and release energy when required. Once you have an understanding of the accumulator and how it works – where it stores excess fluid, compresses the gas, and then releases that fluid back through the system – then you can begin to see the many applications for it.

Regardless of whether they are used to supplement the pump flow, to filter out pulsations or in cases of emergency to provide power, accumulators are a great asset for hydraulic systems. However, each of the three main types; namely the bladder, piston, and diaphragm has its advantages and preferred uses.

If you are either developing or analyzing a hydraulic system, it would be beneficial to think about where in that system an accumulator might enhance it. To choose and apply the right type of accumulator for your application, it is always recommended to seek advice from experienced personnel in the field of fluid power.