What Is a Hydraulic Accumulator?
A Hydraulic Accumulator is a device that converts the pressure energy of a fluid into other high-pressure fluid energy and stores it. It is mainly used in hydraulic and steam fluid equipment.
There are different devices in different technical fields depending on what is stored or accumulated. For example, in the computer field, accumulators temporarily store calculation results and are used for the next calculation; in the electric power field, storage batteries and accumulators; and in wind power generation, systems that circulate oil between windmills and generators to maintain balance.
In hydraulic and steam systems, the pressure energy of oil or steam is stored as nitrogen gas or steam pressure energy, and the gas is expanded to release energy when needed.
Uses of Accumulators
Accumulators are often used in hydraulic systems and steam boilers. In hydraulic systems, accumulators are installed in the high-pressure circuit leaving the pump, and the high hydraulic pressure during operation compresses the nitrogen gas sealed in the Accumulator. When the hydraulic pressure drops, the force of the nitrogen gas is used to raise the hydraulic pressure and maintain it.
In the boiler system, the steam accumulator stores the heat value of steam as high-temperature, high-pressure saturated steam when there is a surplus of steam, and delivers steam with reduced pressure when necessary. In addition, the boiler can operate efficiently and stably because the accumulator absorbs the imbalance between the time variation of steam usage and the steam generation of the boiler.
The use of accumulators in water pumps also softens sudden pressure fluctuations during shutdown and prevents water hammer. The main purpose is to use the energy of the stored gas in the accumulator’s container as an auxiliary power source in an emergency. It is also effective in absorbing and buffering impact pressure, buffering pressure rise in the pipe, and reducing wasteful power consumption of the system.
Principle of Accumulator
Gas accumulators mainly use nitrogen, which is pressurized and contracted or expanded to transfer energy in and out. In the case of hydraulic systems, accumulators are installed in the high pressure circuit leaving the pump.
Inside the Accumulator is a bag called a bladder, which separates the oil side from the gas side. Nitrogen gas is sealed in the bladder, and when the hydraulic pump is driven and the hydraulic pressure rises above the nitrogen gas pressure, the nitrogen gas is compressed.
When the pressure in the hydraulic system drops or the pump stops, the pressure energy of the nitrogen gas causes the bladder to expand to maintain hydraulic pressure. This also has the effect of reducing pulsations in the hydraulic pressure.
The bladder, which seals the nitrogen gas inside the container, is made of a rubber-based material that expands and contracts. The container is made of carbon steel, stainless steel, aluminum, or synthetic materials that are free from corrosion.
The capacity of the container ranges from 0.5 to 450 liters, and the maximum allowable pressure is about 990 atmospheres.
Bladder-type accumulators are characterized by fast energy release and the ability to store and release energy in fast cycles as needed. In addition, the equipment can be made compact, and maintenance is easy.
Other Information on Accumulators
1. Gases in Accumulators
Nitrogen gas is often used as the gas that stores energy in accumulators. Nitrogen gas is a nonflammable and inert gas, which prevents deterioration of the metal used in accumulators. Another advantage is that it is inexpensive and has no risk of explosion.
Since the pressure of nitrogen gas gradually decreases with repeated operation, it is necessary to periodically inspect the accumulators to ensure that the pressure has not decreased. If accumulators are used in the suspension, a drop in gas pressure will make it impossible to absorb shocks from the road surface, resulting in a poor ride quality. If the pressure is low, replenish nitrogen gas.
2. Car System Using Accumulators
Accumulators are used in automobile suspensions and brakes. Accumulators, which act as gas springs, are used in special-purpose vehicles with large body weights and multi-axle vehicles, for which springs may not be able to absorb the shock. In addition, hydraulic suspensions using accumulators can raise and lower the vehicle body freely.
Accumulators are used in brakes to recover energy during braking. In hybrid vehicles, when energy is recovered by the motor, there is a discrepancy between the braking force required by the driver and that of the accumulator. To resolve this discrepancy, accumulators properly assist the motor to ensure optimal braking force.