1. Classification of gear pumps

Gear pumps are generally divided into external meshing type (external gear pump) and internal meshing type (internal gear pump) according to the configuration mode of the meshing pair, and the internal gear pump includes a cycloid gear pump with a special tooth shape.

2. Features of gear pump

The advantages of external gear pump are simple structure, light weight, small size, easy processing and manufacturing, low cost, reliable work, convenient maintenance, strong self-priming ability, insensitive to oil pollution, and can be widely used in occasions with low pressure requirements, such as grinding machines, honing machines and other medium and low pressure machine tools. Its disadvantage is that the internal leakage is large, the bearing bears unbalanced force, the wear is serious, the flow pulsation and noise are large, the flow pulsation of the pump has a greater impact on the normal use of the pump, it will cause the pressure pulsation of the hydraulic system so that the pipeline, valve and other components produce vibration and noise, at the same time, it also affects the smoothness of the movement of the working parts, especially the hydraulic transmission system of the precision machine tool is more unfavorable. Therefore, pay special attention when using it

The advantages of internal gear pump are: compact structure, small size, light weight; Because the internal and external gear steering is the same, the relative slip speed is small, so the wear is small, the life is long, and its flow pulsation and noise are much smaller than those of the external gear pump. The disadvantages of internal gear pumps are complex tooth shape, complex processing, high accuracy requirements, and therefore high manufacturing costs.

3. Application of gear pump

Among the existing types of hydraulic pumps, the working pressure of gear pumps is second only to piston pumps, coupled with their small size and low price, so they are widely used in mobile equipment and vehicles as a pressure oil source for hydraulic working systems and steering systems. On the other hand, due to the large speed and displacement range of gear pumps, strong oil absorption capacity and low cost, they are also often used as auxiliary pumps in various hydraulic systems, such as the replenishment pump in the closed circuit, the low-pressure control oil source in the pilot control system, etc. However, in the field of fixed hydraulic equipment, due to the large flow pulsation, high noise and limited life of external gear pumps, it has become less and less popular as a main pump, and its use is limited to auxiliary pumps and pre-pressure pumps operating at low pressure. In contrast, the internal gear pump is one of the hydraulic pumps with low noise and good comprehensive performance. Except for the slightly higher price, it is almost superior to external gear pumps in other aspects. The development of modern manufacturing technology will greatly narrow the cost gap between internal and external gear pumps, and in the industrial field, the increasing popularity of speed control electric transmission technology largely makes up for the shortcomings of the internal gear pump itself can not be variable. It is expected that the application of internal gear pumps in both stationary and mobile equipment will expand rapidly in the future. In hydraulic engineering, cycloid gear pump with the advantages of small size, low price and strong self-priming ability, is widely integrated in the back cover of the closed oil circuit through shaft piston pump, as a low-pressure refill pump (to provide control pressure), and sometimes also used as the main pump of some machine tool hydraulic systems. This kind of pump can achieve one-way fuel supply, and it is independent of input steering, which is of special significance for the emergency steering and braking system that needs to be driven by wheels on some vehicles or mobile machinery. The cycloid gear pair (Olbit meshing pair) with fixed pin tooth ring has a large displacement per unit volume, but because of its low permissible speed, it is mostly used as a low-speed hydraulic motor, and is only used as a metering pump in the hydraulic steering system of the vehicle. When the power oil source in the system fails, this pump can be manually made an emergency oil source.