Two gear pumps

The characteristics of the gear pump are: small size, light weight, simple structure, convenient manufacture, low price, reliable work, good self-priming performance, insensitivity to oil pollution, and easy maintenance.

The disadvantages are: large flow and pressure pulsation, large noise, invariable displacement and so on.

Compared with the external gear pump, internal gear pumps mainly have the advantages of small volume, small flow pulsation, and low noise, but the processing is difficult and the use is limited. Here, the tooth surface contact line at the meshing point always serves to separate the high and low pressure chambers, so that no special flow distribution mechanism needs to be provided in the gear pump.

1. External mesh gear pump flow

Displacement: V=Ï€DhB=2Ï€m2zB

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

Flow rate: q=Vnηv=6.66zm2Bnηv

The above calculation is the average flow of the external gear pump.

Features:

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

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

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

4) In addition, in the positive displacement hydraulic pump, the flow rate of the gear pump pulsates the most.

2, the phenomenon of trapped oil pump and unloading

★ hazards of trapped oil phenomenon:

The pressure in the dead volume is increased sharply, causing the bearing to be subjected to a large additional load. At the same time, power loss, liquid heating, and other undesirable phenomena occur; air dissolved in the liquid is evolved to generate air bubbles, resulting in cavitation, causing vibration and noise.

★ eliminate the trapped oil phenomenon:

On the side plate of the gear pump or the floating sleeve, open and close the groove. Asymmetric type, it must be ensured that the oil suction chamber and the pressure oil chamber cannot be collaborated with each other at any time; such a gear pump cannot be reversed.

3, gear pump leakage and compensation measures

There are three parts of the gear pump that cause leakage: between the gear end face and the end cover; between the tooth tip and the housing bore and the gear engagement. The leakage between the gear end face and the end cap is the largest, accounting for 75-80% of the total leakage.

4. Measures to increase the pressure of external gear pump

Face gap automatic compensation principle:

Using a special channel to introduce the pressure oil in the pressure chamber of the gear pump to the outside of the floating sleeve, acting on the area of ​​a certain shape and size, and generating a hydraulic force to press the sleeve against the gear end face. This force must be greater than the gear The action of the end face acting on the inner side of the sleeve can ensure that under various pressures, the sleeve will always adhere to the gear end surface automatically and reduce the leakage through the end face in the gear pump to achieve the purpose of increasing the pressure.

5, radial imbalance force

★Hazard:

When the radial imbalance force is large, the shaft can be bent and the top of the tooth can contact with the shell, at the same time, the wear of the bearing can be accelerated, and the bearing life can be reduced.

★Measures:

In order to reduce the influence of radial imbalance force, the method of reducing the pressure port is usually adopted.

Reduce the number of gear teeth, thus reducing the diameter of the top circle and reducing the bearing area.

Increase the radial clearance appropriately.

6, internal gear pump

Internal gear pumps include involute gear pumps and cycloidal gear pumps.

Cycloid gear pumps, also known as rotor pumps, have a tooth difference of one tooth.