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What is a hydropneumatic accumulator?

Hydraulics is a broad sector, and one that is sometimes difficult to understand and to grasp. The components and materials, but also the fields of activity, that make it up are diverse and their respective interweavings make it something of a hermetical web. But that's only on the surface! Accumulators are an interesting example. Both hydraulic and hydropneumatic accumulators have their own functions and interests. But what exactly is a hydropneumatic accumulator? We'll take a closer look.

What is a hydropneumatic accumulator?

First of all, let's try to define what a hydropneumatic accumulator is. What does it look like?

This accumulator is also called a nitrogen ball. But why? As you'll see later, the reason for this nickname is very simple to understand.

A hydropneumatic accumulator is generally made up of very simple components. They consist of a metal tank, usually made of steel, stainless steel or aluminium. This tank is split in two by a separator, usually a piston.

The tank is split because of the difference in its contents. The first tank will contain the liquid fluid needed by the engine, while the second will be filled with nitrogen. Remember the nickname of the nitrogen ball for this accumulator? Here's why!

Nitrogen is an extremely compressible gas, so it allows the first volume, which stores the engine oil, to be deformed, allowing much more oil to be stored. This compressibility means more oil can be stored, but also more oil can be returned. If nitrogen can be compressed under pressure, it is released more quickly when expanded.

Obviously, in this scheme, the piston or diaphragm separating the two is essential, and should be inspected regularly to ensure that it is in good condition. The two tanks must never become communicating vessels, which would impair their operation.

Despite this precaution, it should be noted that nitrogen is not explosive when in contact with oil, so it is still the most strongly recommended gas for this type of accumulator. This is for obvious safety reasons.

There are three main types of accumulator:

  • Membrane accumulators
  • Bladder accumulators
  • Piston accumulators

Each of these models has its own specific features in terms of capacity and use. Membrane models, for example, are likely to contain less nitrogen and have lower pressure. Bladder models, on the other hand, will be more rigid and less flexible, but will have a greater capacity and allow a maximum pressure of 1,500 bars, compared with 750 at the peak of activity for membrane models. Finally, piston models are reputed to be more watertight and have a capacity that can be described as intermediate to the other two models.

So, the choice of one or other of these models should be based on considerations linked to the use you intend for them! Each has its own advantages, depending on the situation.

But what exactly are they used for?

The uses reserved for hydropneumatic accumulators

Having seen the characteristics of these accumulators, let's now look at their practical use.

We have seen that these accumulators are capable, because of their double reservoir, of containing large reserves of energy under pressure in a smaller volume, and of releasing this energy very efficiently when the need arises.

But what are they used for?

Our accumulators are mainly found in the industrial and agricultural sectors, where they are mainly used for hydraulic suspension, and as an emergency energy reserve, because of their famous capacity and speed of delivery.

Now you know everything!

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