Gear pump is characterized by: small size, light weight, simple structure, easy manufacture, low price, reliable work, self-priming performance is better, not sensitive to oil pollution, easy maintenance.

The disadvantage is: large flow and pressure pulsation, noise, displacement and other variables.

Internal gear pump compared with the external gear pump, the main small, small flow pulsation, noise, etc., but the processing difficulties, the use is limited. Here the meshing point of the tooth surface contact line has been playing the role of high-pressure, low pressure chamber, so the gear pump does not need to set a special flow control mechanism.

1, external gear pump flow

Displacement: V = πDhB = 2πm2zB

In fact, the volume between teeth is slightly larger than the size of the teeth, so usually take 3.33, then: V = 6.66zm2B

Flow rate: q = Vnηv = 6.66zm2Bnηv

The above calculation is the average external gear pump flow.

Features:

1) The average flow of the gear pump is proportional to the number of teeth and to the square of the modulus.

2) The flow of gear pump is proportional to tooth width, but the increase of tooth width is limited by the increased hydraulic radial force of gear. Generally, tooth width B = (6 ~ 10) m and small value at high pressure.

3) increasing the speed can increase the pump flow, but by the pump suction performance limits. Gear pump speed is generally 1000 ~ 1500r / min.

4) In addition, in the positive displacement hydraulic pump, the gear pump has the largest flow pulsation.

2, gear pump trapped oil phenomenon and unloading

★ trapped oil hazards of the phenomenon:

So that the pressure in the closed volume increased dramatically, so that the bearing is subject to a large additional load, while generating power loss and liquid heating and other undesirable phenomena; dissolved in the liquid air will precipitate bubbles, resulting cavitation, causing vibration and noise.

★ eliminate the trapped oil phenomenon:

Open the notch on the side plate of the gear pump or on the floating bushing. Asymmetrical, it must be ensured that the suction and pressure chambers can not be brought into direct contact with each other at all times; such gear pumps can not be reversed.

3, gear pump leakage and compensation measures

Gear pump there are three parts of the leak: the gear between the end face and the end cover; tooth top and housing within the hole and gear meshing Department. Among them, the maximum leakage between the gear end face and the end cap accounted for 75 ~ 80% of the total leakage.

4, improve the external gear pump pressure measures

End clearance automatic compensation principle:

The use of special access to the gear pump hydraulic oil pressure chamber led to the outer side of the floating sleeve, the role of a certain shape and size of the area, resulting in hydraulic force, the sleeve pressed to the gear end face, the force must be greater than the gear The effect of the end face acting on the inner side of the sleeve ensures that the sleeve always presses the end face of the gear automatically under various pressures so as to reduce the leakage of the end face of the gear pump so as to increase the pressure.

5, radial imbalance force

★ Hazard:

Large unbalanced radial force can make the shaft bend, tooth top contact with the shell, while accelerating bearing wear and reduce bearing life.

★ measures:

In order to reduce the impact of radial unbalance force, usually take to reduce the pressure port approach.

Reduce the gear teeth, thus reducing the addendum diameter, bearing area decreases.

Appropriate to increase the radial clearance.

6, internal gear pump

Internal gear pump with involute gear pump and cycloid gear pump two.

Cycloid gear pump, also known as the rotor pump, the two gears differ by a tooth.

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