In hydraulic system design, energy transfer between the pump and actuators is not always linear. Although hydraulic oil is extremely difficult to compress, its bulk modulus changes under high pressure, and mechanical actions are often discontinuous. This leads to energy supply imbalances and severe pressure pulsations in the system.
An accumulator, as an energy storage device, essentially introduces a “controllable elastic link” into the hydraulic system. It stores liquid energy by compressing gas (usually nitrogen). So, in which specific application scenarios is an accumulator no longer an “optional accessory” but a “core standard component”?
1. Instantaneous High Power Demand Systems
In many periodically operating hydraulic devices, the system’s flow demand is extremely uneven.
(1) Operating Characteristics:
The operating cycle includes very short periods of rapid advance or stamping, during which the required flow rate far exceeds the system’s average flow rate; while at other times (such as loading, cooling, and pressure holding), the system’s flow demand is extremely low.
(2) Application Examples:
Injection molding machines, die-casting machines, heavy-duty stamping presses.
(3) Necessity of Configuration:
Without an accumulator, the hydraulic pump’s displacement must be selected based on the maximum instantaneous flow rate, resulting in a huge motor capacity and severe overflow losses and heat generation during low-flow phases.
(4) Technical Logic:
The accumulator stores the oil supplied by a small-displacement pump during low-demand phases and releases it instantaneously during high-demand phases. This “peak shaving and valley filling” design can reduce motor power by 30%-60%, significantly improving the system’s energy efficiency ratio.
2. Emergency Power and Safety Protection Systems
In systems involving significant personal safety or expensive equipment assets, accumulators serve as the “last line of defense.”
(1) Operating Characteristics:
In the event of a sudden power outage, main pump failure, or pipeline depressurization, the actuators must perform predetermined safety actions.
(2) Application Examples:
Wind turbine generator sets (pitch control), emergency shut-off valves for metallurgical blast furnaces, power station gates, large forging machines.
(3) Necessity of Configuration:
In the event of loss of the main power source, the potential energy stored in the accumulator is sufficient to drive the actuators to complete a final reset or shutdown.
(4) Engineering Standards:
Many industry standards mandate the use of accumulators with sufficient capacity for such potentially hazardous hydraulic equipment to ensure “fail-safe” operation in accident situations.
3. High-Precision and Long-Term Pressure Holding System
In some applications, the system needs to maintain a stable high pressure for a long period of time without the actuator moving.
(1) Operating Characteristics:
After completing clamping or forming, the actuator (such as a hydraulic cylinder) enters a pressure holding state that lasts for several minutes or even hours.
(2) Application Examples:
Hydraulic clamps, rubber vulcanizing machines, hydraulic supports.
(3) Necessity of Configuration:
Due to the unavoidable slight internal leakage of the directional valve and seals, the pressure will decrease over time. If the pressure is maintained by continuous pump operation, it will not only be noisy but also cause severe mechanical wear.
(4) Technical Logic:
The accumulator can compensate for the volume loss caused by leakage in the system. When the pressure drops to the preset lower limit, the pump is started through a pressure relay to replenish energy; most of the time, the pump is in a stopped or unloaded state, and the accumulator statically maintains the pressure.
4. Sensitive and High-Frequency Reversing Systems
Water hammer in hydraulic systems is a major cause of pipeline rupture and damage to precision sensors.
(1) Operating Characteristics:
① Pressure Pulsation: Due to the limited number of plungers in a piston pump, the output flow exhibits sinusoidal pulsation, inducing system vibration.
② Hydraulic Shock: When the directional valve is switched rapidly or the load suddenly stops, kinetic energy is converted into pressure potential energy, generating instantaneous peak pressure.
(2) Application Examples: High-pressure cleaners, long-distance hydraulic pipelines, automated production lines.
(3) Necessity of Configuration:
Accumulators installed at the pump inlet or the front end of the reversing valve utilize the compressibility of nitrogen to act as “air springs,” absorbing shock waves.
(4) Technical Specifications:
With proper configuration, system vibration can be reduced by more than 70%, significantly improving the service life and control accuracy of precision sensors (such as proportional valves and servo valves).
5. Determine the parameters for selecting the accumulator needed for the system.
(1) Application of the gas law equation:
Depending on the speed of operation, the selection calculation needs to distinguish between adiabatic processes (rapid charging and discharging, PV^1.4 = C) and isothermal processes (slow pressure holding, PV = C).
(2) Scientific setting of nitrogen charging pressure (P0):
For energy storage: P0 is usually taken as 90% of the minimum operating pressure P1.
For shock absorption: P0 is usually taken as 60% – 80% of the system’s rated operating pressure.
(3) Type selection:
Blouse type: Low inertia, sensitive response, suitable for absorbing high-frequency pulsations.
Piston type: Large volume, high pressure resistance, but high frictional resistance, suitable for heavy machinery energy storage.