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1. The working principle of the accumulator

The accumulator is a hydraulic accessory designed to accumulate pressurized liquid. The liquid is incompressible. The accumulator uses the compressibility of the gas to achieve the purpose of storing the liquid. When the pressure rises, the oil enters the energy storage. The gas is compressed by this, and when the pressure drops, the compressed gas expands and the oil is hydraulically fed into the circuit.

2. Capacity selection of accumulator

Definition of state parameters

P0=pre-charge pressure V0=effective gas volume

P1=minimum working pressure V1=gas volume at P1

P2=maximum working pressure V2=gas volume at P2

tmin=minimum working temperature t0=pre-charge gas temperature

tmax=maximum working temperature n=variable index

① The state before use (nitrogen and liquid have not entered).

② The capsule is pre-filled with nitrogen gas, and the oil valve is closed to prevent the capsule from detaching.

③ When the minimum working pressure is reached, a small amount of oil should be kept between the outside of the capsule and the oil valve (about 10% of the nominal capacity of the accumulator), so that the capsule will not hit the valve during each expansion process and cause damage to the capsule.

④ The accumulator is at the highest working pressure. The volume change at the minimum and maximum working pressures corresponds to the effective fluid volume. △V=V1—V2

3. Selection of pre-charge pressure

The bladder accumulator NXQ series allows volume utilization of 75% of the actual gas capacity. Therefore, the ratio between the pre-charge nitrogen pressure and the maximum working pressure is limited to 1:4, and the pre-charge pressure should not exceed 90% of the minimum system pressure. Following this rule guarantees a long capsule life. Other compression ratios can be achieved with special measures.

In order to fully utilize the capacity of the accumulator, it is recommended to use the following values.

Energy storage: P0tmax=0.9×P1 Shock absorption: P0tmax=(0.6～0.9)×Pm(Pm=average working pressure of free circulation)

Absorption pulsation: P0tmax=0.6×Pm (Pm=average working pressure) or P0tmax=0.8×P1 (at various working pressures)

The limit value of pre-charge pressure: P0≤0.9×P1, the allowable compression ratio is P2:P0≤4:1

4. Calculation formula for accumulator capacity selection

The compression and expansion process in the accumulator should follow the law of changing gas states.

The ideal gas is: P0×Vn 0=P1×Vn 1=P2×Vn 2

Among them, the influence index of the variable index "n" on the gas characteristics over time should be considered.

The state change of the slow expansion and compression process is close to isothermal, and the variable index can be n=1

And the rapid expansion and compression process occurs adiabatic state change, the multivariable index n=1.4 (suitable for diatomic gas nitrogen)