Created on：2021-04-09 13:46

# Main parameters and common problems of hydraulic pump

Main parameters and common problems of hydraulic pump

(3) Displacement and flow

① Displacement V the volume of the liquid discharged from the main shaft of the hydraulic pump, which is calculated by the change of the geometric dimension of the sealing chamber, is called the displacement of the hydraulic pump, that is, the volume of the liquid discharged from the shaft of the pump when it rotates one revolution without leakage. The legal measurement unit of discharge is m3 / R (cubic meter per revolution), and the common unit in engineering practice is ml / R (milliliter per revolution) (1ml / r = 1000mm3 / R, 1m3 / r = 106ml / R).

GB / T 2347-1980 specifies the nominal displacement series of hydraulic pumps and hydraulic motors (table below).

Hydraulic pump and hydraulic motor nominal displacement series ml · R-1

 zero point one 1.0 10 100 1000 （112） （1120） 1.25 12.5 125 1250 （14） （140） （1400） 0.16 1.6 16 160 1600 （18） （180） （1800） 2.0 20 200 2000 （22.4） （224） （2240） 0.25 2.5 25 250 2500 （28） （280） （2800） 3.15 31.5 315 3150 （35.5） （355） （3550） 0.4 4 40 400 4000 （45） （450） （4500） 5.0 50 500 5000 （56） （560） （5600） 0.63 6.3 63 630 6300 （71） （710） （7100） 8.0 80 800 8000 （90） （900） （9000）

② Theoretical flow QT the volume of liquid discharged by a hydraulic pump in unit time, which is calculated by the geometric dimension change of its sealing cavity, that is, the volume of liquid that can be discharged in unit time under the condition of no leakage, is called the theoretical flow of the hydraulic pump, which generally refers to the average theoretical flow without considering the pulsation of the liquid output by the hydraulic pump. In engineering practice, the pump flow under zero pressure difference is often regarded as the theoretical flow.

The legal measurement unit of flow (theoretical flow, instantaneous flow, average flow, actual flow and leakage flow, etc.) is m3 / S (cubic meter per second). The actual engineering unit is 106 ml / min.

The relationship between theoretical flow QT and displacement V of hydraulic pump is as follows:

qt=(Vn/60)×l0-6 (m3/s) (1-1)

Where V -- displacement of hydraulic pump, ml / R;

N -- speed of hydraulic pump, R / min.

③ The instantaneous flow of qinst pump in each instantaneous flow is called the instantaneous flow of hydraulic pump, generally refers to the instantaneous theoretical (geometric) flow, which has a certain pulsation.

④ Average flow QAV the flow calculated according to the average time is called the average flow of the hydraulic pump.

⑤ When the rated flow QN hydraulic pump operates under rated pressure and rated speed, the output flow of the hydraulic pump must be guaranteed according to the test standard.

⑥ Actual flow Q the actual discharge flow of the hydraulic pump is called the actual flow of the hydraulic pump.

Because of the leakage and the compression of the liquid, the rated flow QN and the actual flow Q of the hydraulic pump are less than the theoretical flow QT.

The actual flow Q can be expressed as

q=qt-q1=Vn-k1△p (1-2)

Where Q1 -- flow loss due to leakage and compression of hydraulic pump to external or low pressure chamber;

K1 -- leakage coefficient of pump;

Δ p - the pressure difference of the pump. When the inlet pressure (gauge pressure or relative pressure) of the pump is close to zero, the outlet working pressure P of the pump can be used to replace it, the same below.

The meaning of other symbols is the same as before.

It can be seen from equation (1-2) that both Q1 and Q are related to the working pressure P of the pump. When the working pressure increases, the loss flow Q1 increases, while the actual output flow Q decreases.

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