What is an accumulator of the hydraulic system?
An accumulator of the hydraulic system is a reservoir with a diaphragm or piston and contains an inert pressurized gas (usually nitrogen) that is used for energy storage. Hydraulic fluid is kept outside the tank on the other side.
What are the roles and duties of accumulators in the hydraulic system?
Accumulators have the same role as a car battery, with the difference that instead of electrical energy, accumulators store hydraulic energy through a fluid under pressure, and to maintain the pressure, complete the flow of the pump and increase its capacity. In addition to these, other tasks of accumulators can be mentioned as controlling and minimizing pressure fluctuations and shocks in closed hydraulic systems, as well as providing auxiliary hydraulic power in emergencies. The use of accumulators significantly increases the efficiency of hydraulic systems.
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Types of accumulators and their usage
Currently, there are three main types of hydraulic accumulators, which are:
- Weight Loaded Accumulator
- Spring Loaded Accumulator
- Gas Loaded Accumulator
These accumulators are classified based on how they work. In the following, we will briefly introduce the types of accumulators.
Weight Loaded Accumulator
As the name of this accumulator suggests, its structure usually uses a mechanism of piston and weight (load) in the form of potential energy storage. Therefore, pressure is applied to the hydraulic fluid when the piston moves inside the cylinder.
As weight accumulators can take up a lot of space, they are typically used in limited, high-volume applications such as heavy presses.
Spring Loaded Accumulator
The structure of spring accumulators generally consists of a spring piston inside the cylinder. The hydraulic fluid enters the accumulator tank from the other side of the cylinder and is stored under the pressure of the force caused by the spring. Therefore, in this accumulator, the pressure reaches its peak when the spring is optimally compressed. As a result, when the spring reaches its maximum length, the pressure on the fluid also reaches the minimum possible.
Spring accumulators are usually used in places and conditions where we are faced with space limitations or in situations where we should work in smaller volumes and dimensions, such as mobile and motor systems.
Gas Loaded Accumulator
Gas is used as the fluid in these accumulators. Gas accumulators, which are also called hydropneumatic accumulators, are divided into two types, separating and non-separating.
Non-separator type accumulator
These accumulators are one of the types that when the pressurized fluid (gas) enters the cylinder, creates pressure in them. As the pressure increases, the oil port opens, which causes oil to enter the cylinders and the gas volume decreases. This increase in pressure continues until the pressure caused by the distance causes the cylinder to move.
Separator type accumulator
Separator gas-type accumulators are those in which the piston acts as a barrier between hydraulic fluid and gas. Therefore, when the hydraulic oil applies pressure to the piston, this action causes the gas to be compressed automatically.
Three important types of separator gas accumulators are:
In this accumulator type, a bladder is used as a flexible separator between gas and hydraulic oil. The bladder is inside the steel casing and there is a valve at its entrance.
These types of accumulators use a diaphragm as an elastic separator, and in them, the diaphragm is completely closed between the walls of the tank under pressure.
In this type of accumulator, the piston separates hydraulic oil and compressed gas in this accumulator. The structure of this accumulator is very similar to the spring accumulator, with the difference that pressurized gas is used instead of a spring.
Application of Accumulators in the Machinery Industry
The accumulator system is used in industrial hydraulic machines such as hydraulic shears (guillotine). In the hydraulic section of the machine, a suitable fluid (oil) is used to move the pistons. In the traditional method, the moving process of the piston reciprocation is provided by fluid force. In this method, with the continuous operation of the machine, the oil gets hot and causes damages the hydraulic components of the machine. Also, heating reduces the density of the oil and reduces the shearing power of the machine. In the new hydraulic system method, they create an accumulator system next to the nitrogen gas system. In this method, nitrogen gas is compressed when the jaw of the device is lowered and the stored force helps the hydraulic system to raise the device. In this case, to raise the jaw of the device, the hydraulic system is removed from the circuit and the nitrogen gas pressure causes the upper jaw of the device to rise. Therefore, we do not encounter the problem of overheating the device during continuous operation. There are several reasons for using nitrogen gas in machines manufactured by Dayyani Grand Machinery Company. The most crucial factor that has caused the use of nitrogen gas is the stability of nitrogen gas and its lack of reaction with pressurized and possibly hot oil.
The reason that other machine manufacturers don’t use this method is mainly due to the lack of familiarity with the technical knowledge and the higher cost of this system compared to the traditional method.
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At the end of this article, a video of the introduction and operation of 3 types of accumulators in the hydraulic system is brought to you along with examples.