Understanding the function of a hydraulic accumulator

Hydraulic systems are incredibly complex structures, comprised of many complex components. If you’re relatively new to this field of engineering then it’s likely that you’re aware of the five key components of any hydraulic system: the reservoir, pump, motor, cylinder and control valves.

However, there’s more than meets the eye when it comes to hydraulics and plenty of other components play crucial roles in keeping these systems in operation. One of these fundamental components is an accumulator.

In this article, we’ll take a closer look at what accumulators are, and what they offer to a hydraulic system.

What is a hydraulic accumulator?

To put it simply, a hydraulic accumulator is an energy storage device. It’s a relatively simple pressure vessel by design that stores energy in the form of pressurised hydraulic fluid.

When the pressure within a hydraulic system increases, the accumulator absorbs the pressurised fluid and stores it. Accumulators have the ability to hold this fluid under pressure to keep it compressed, saving it for later use.

This reserve tank of energy can be used for a number of different functions, which we’ll discuss below.

How does a hydraulic accumulator work?

An accumulator comprises a piston which is housed in a cylindrical steel chamber. Depending on the type of accumulator, the piston will either be weight or spring-loaded.

The accumulator is connected to the hydraulic pump at the inlet, which continuously supplies the fluid. At the outlet, the accumulator is connected to the machinery (for example, a crane). As the fluid is pumped into the accumulator, pressurised energy is created which will either be used to power the machine or stored in the accumulator for later use.

In a spring-loaded accumulator, the springs create pressure on the piston to pump out the fluid. The rate at which the fluid is pumped depends on the spring compression rate, and this type of accumulator is usually better suited to mobile applications and those with lower volumes of fluid.

Bladder accumulators are the most commonly used type of spring-loaded accumulator and the one you’re most likely to come across in a hydraulic system. The bladder is filled with pre-charged nitrogen and fitted within a steel pressure vessel. The nitrogen is compressed by the hydraulic fluid and when a pressure drop occurs, the compressed gas expands and pushes the stored hydraulic fluid back into the circuit.

A weight-loaded accumulator is larger and heavier, making it more suitable for large volumes of fluid in heavy-duty applications. This type of accumulator consists of a large cylinder and a piston rod which is loaded with a dead weight. As fluid is pumped into the accumulator, the piston raises due to the weight. As the piston reaches its uppermost position, the deadweight develops a gravitational force and applies constant pressure on the fluid.

The functions of an accumulator in a hydraulic system

An accumulator has multiple important responsibilities in a hydraulic system, as the stored energy can be used to perform a number of different functions.

Most commonly, hydraulic accumulators are used to supplement pump flow. As pumps supply continuous flow, not all circuits need this. For example, some may require an on-off flow for periods of time. In these cases, the pump keeps the accumulator pressurised for later use.

Critically, the stored energy can also be used as an emergency supply when the pressure in a system begins to drop and there are no other means of power supply. Accumulators can quickly re-feed energy into the circuit to prevent a breakdown, and then the energy collection process starts again.

Accumulators can also cushion shocks and absorb pulsations in a hydraulic circuit. A sudden change to operations or valve positionings can cause pressure waves. A well-placed accumulator (i.e. in a shock-prone area) can help to reduce this and ensure smooth pump pulsations.

Another key function of hydraulic accumulators is to help maintain system pressure. Due to the rising or falling temperatures of hydraulic fluid, or a leakage in the system, pressure changes can occur. With an accumulator absorbing or releasing small amounts of hydraulic fluid, the required pressure rating can be sustained.

Overall, accumulators help to take the weight off the pump. Without an accumulator, the pump would be working overtime to keep the system operational which can negatively affect its performance and lifespan.

 

The three types of hydraulic accumulator

There are three main types of hydraulic accumulators, all with different capabilities. The type of accumulator chosen for your application will depend on various factors such as maximum operating pressure, fluid volume and the demands of the application.

Bladder type accumulator

Bladder type accumulators are the most popular type of accumulator, and are most commonly chosen when the application requires a high power output at medium to high pressure.

Diaphragm accumulator

This type of accumulator is typically used in mobile applications and those with low fluid volume requirements, as they are lighter and smaller in size with a relatively small fluid storage capacity.

Piston accumulators

Usually used in high-pressure, heavy-duty applications, piston accumulators are capable of handling substantially higher compression ratios and flow rates.

Where to buy a hydraulic accumulator

Selecting a suitable hydraulic accumulator is key to ensuring operating efficiency and longevity. If you’re not familiar with accumulator selection, we can help.

Flowtech can supply a range of bladder accumulators and accessories from global-leading manufacturers such as Olaer Fawcett Christie. We work with a range of best-in-class brands and have the capabilities of building or modifying products to meet your exact requirements.