1. Working principle of accumulator

An accumulator is a hydraulic accessory designed to store compressed liquid, which is incompressible. The accumulator uses the compressibility of gas to store the liquid. When the pressure increases, the oil enters the accumulator and the gas is compressed. When the pressure decreases, the compressed gas expands and the oil flows 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 operating temperature t0=pre charge gas temperature

Tmax=maximum operating temperature n=variability 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 (about 10% of the nominal capacity of the accumulator) should be retained between the capsule and the oil valve to prevent the capsule from hitting the valve during each expansion process and causing damage to the capsule.

④ The accumulator is at its maximum working pressure. The volume change at the minimum and maximum working pressures is equivalent to the effective amount of oil. △V=V1—V2

　　3. Selection of pre charging pressure

The NXQ series bladder type accumulator allows a volume utilization rate of 75% of the actual gas capacity. Therefore, the ratio between the pre filled nitrogen pressure and the maximum working pressure is limited to 1:4, and the pre filled pressure must not exceed 90% of the minimum system pressure. Following this regulation can ensure a longer lifespan of the capsules. Other compression ratios can be achieved through special measures.

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 flow)

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 selecting the capacity of the accumulator

The compression and expansion process inside the accumulator should follow the law of gas state variability.

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 changes of the slow expansion and compression process are close to isothermal, and the variability index can be n=1

And the rapid expansion and compression processes undergo adiabatic state changes, with a variable exponent of n=1.4 (suitable for nitrogen gas with diatomic properties)