What is an accumulator?

1. What is an accumulator
Hydraulic accumulator is a device for storing energy. In the accumulator, the stored energy is stored in the form of compressed gas, compressed spring, or lifted load, and applies force to a relatively incompressible fluid.
Accumulators are very useful in fluid power systems. They are used to store energy and eliminate pulses. They can be used in hydraulic systems to reduce the size of the fluid pump by supplementing the pump fluid. This is done by storing the energy in the pump during the low demand phase. They can act as a slowdown and absorber of fluctuations and pulses. They can cushion the blow and reduce the vibration caused by the sudden start or stop of the power cylinder in the hydraulic circuit. When the liquid is affected by temperature rise and fall, the accumulator can be used to stabilize pressure changes in the hydraulic system. They can dispense fluid under pressure, such as grease and oil.

At present, the most commonly used accumulators are pneumatic-hydraulic types. The function of gas is similar to a buffer spring, it works with fluid; the gas is separated by piston, thin diaphragm or air bag.

2. Working principle of accumulator

Under the action of pressure, the volume change of the liquid (under the constant temperature) is very small, so if there is no power source (that is, the supplement of high-pressure liquid), the pressure of the liquid will drop rapidly.

The elasticity of gas is much greater, because the gas is compressible, in the case of a large volume change, the gas may still maintain a relatively high pressure. Therefore, when the accumulator is supplementing the hydraulic oil of the hydraulic system, the high-pressure gas can continue to maintain the pressure of the hydraulic oil when the volume of the liquid has changed. It becomes smaller, causing the hydraulic oil to lose pressure quickly.

As for nitrogen, the main reason is that nitrogen is stable in nature and does not have oxidation or reduction properties. This is very good for maintaining the performance of hydraulic oil and will not cause oxidation/reduction denaturation of hydraulic oil!

Nitrogen is the pre-charge pressure, which is installed in the airbag of the accumulator and is separated from the hydraulic oil! When you fill the accumulator with hydraulic oil, due to the pressure of the nitrogen air bag on the hydraulic oil, that is, the pressure of the hydraulic oil is equal to the nitrogen pressure. As the hydraulic oil rushes in, the nitrogen air bag is compressed, and the nitrogen pressure increases. The oil pressure increases until the hydraulic oil reaches the set pressure!

The role of the accumulator is to provide a certain pressure of hydraulic oil, which is produced by the force of nitrogen!

3. The main function of accumulator

1. For auxiliary power supply
The actuators of some hydraulic systems act intermittently and the total working time is very short. Although the actuators of some hydraulic systems do not act intermittently, their speeds vary greatly within a working cycle (or within a stroke). After the accumulator is installed in this system, a pump with lower power can be used to reduce the power of the main drive, so that the entire hydraulic system is small in size, light in weight, and inexpensive.

hydraulic control butterfly valve

2. As an emergency power source
For some systems, when the pump fails or the power fails (the oil supply to the actuator is suddenly interrupted), the actuator should continue to complete the necessary actions. For example, for safety, the piston rod of a hydraulic cylinder must be retracted into the cylinder. In this case, an accumulator with appropriate capacity is required as an emergency power source.

3. Replenish leakage and maintain constant pressure
For systems where the actuator does not operate for a long time, but to maintain a constant pressure, an accumulator can be used to compensate for leakage, so that the pressure is constant.

4. Absorb hydraulic shock
Due to the sudden change of the direction of the reversing valve, the sudden stop of the hydraulic pump, the sudden stop of the movement of the actuator, or even the artificial need for emergency braking of the actuator, etc., the liquid flow in the pipeline will change sharply, resulting in shock pressure (oil hit). Although there is a safety valve in the system, it is still inevitable to produce a short-term surge and shock of pressure. This shock pressure often causes failures or even damage of the instruments, components, and sealing devices in the system, or rupture of the pipeline, and also causes the system to produce obvious vibrations. If an accumulator is installed before the shock source of the control valve or hydraulic cylinder, the shock can be absorbed and alleviated.

5. Absorb pulsation and reduce noise
The pulsating flow of the pump will cause pressure pulsation, causing uneven movement speed of the actuator, causing vibration and noise. Connect a sensitive and small inertia accumulator in parallel at the outlet of the pump to absorb flow and pressure pulsations and reduce noise.

Post time: Sep-26-2020