Gear pump knowledge inventory

Update: 26-03-2021

Gear pump is a kind of hydraulic pump widely used in hy […]

Gear pump is a kind of hydraulic pump widely used in hydraulic system. It is generally made as a quantitative pump. According to different structures, gear pumps are divided into external gear pumps and internal gear pumps, and external gear pumps are the most widely used.

The tooth top cylinder and two end faces of a pair of gears meshing with each other are close to the inner wall of the pump casing, and a series of sealed working cavities K which are not connected to each other are enclosed between each tooth groove and the inner wall of the casing. The D and G cavities separated by the meshing gear teeth are the suction chamber and the discharge chamber that communicate with the pump suction inlet and the discharge outlet, respectively.

When the gear rotates, because the meshing gear teeth gradually exit the meshing state, the volume of the suction chamber D gradually increases and the pressure drops. Under the effect of the pressure difference between the liquid surface pressure in the suction pool and the low pressure in the D cavity, the liquid enters the suction chamber D from the suction pool through the suction pipe and the pump suction inlet. Then it enters the closed working space K and is brought to the discharge chamber G by the rolling of the gear. Because the two gear teeth gradually enter the meshing state from the upper side, the gear teeth of one gear gradually occupy the cogging space of the other gear, so that the volume of the discharge chamber on the upper side is gradually reduced, and the internal liquid pressure increases, so the pump The discharge port is discharged out of the pump. The gears roll successively, and the above-mentioned suction and discharge processes are continuously carried out one after another.
The most basic form of a gear pump is that two gears of the same size mesh and rotate with each other in a close-fitting shell. The inside of the shell is similar to the "8" shape. Two gears are installed inside. The outer diameter and two sides of the gear are connected to each other. The shell fits tightly. The material from the extruder enters the middle of the two gears at the suction inlet, and fills this space, moves along the housing with the rotation of the teeth, and is finally discharged when the two teeth mesh.

The working principle of the gear pump is a separate three-piece structure. The three pieces refer to the pump cover 4, 8 and the pump body 7. The pump body 7 is equipped with a pair of gears 6 with the same number of teeth, close to the pump body and meshing with each other. The pair of gears, the two head covers and the pump body constitute a sealed cavity, and the sealed cavity is divided into two parts by the tooth tops and meshing lines of the gears, namely the oil suction cavity and the oil pressure cavity. The two gears are respectively keyed on the driving shaft 12 and the driven shaft 15 supported by needle bearings, and the driving shaft is driven to rotate by a motor.

When the driving gear of the pump rotates in the direction of the arrow shown in the figure, the gear on the right side (suction chamber) of the gear pump is disengaged, and the teeth of the gear exit between the teeth, which increases the sealing volume and forms a partial vacuum. Under the effect of external atmospheric pressure, it enters between the teeth through the oil suction pipeline and the oil suction cavity. As the gear rotates, the oil sucked between the teeth is taken to the other side and enters the oil pressure chamber. At this time, the gear teeth enter into meshing, so that the sealing volume is gradually reduced, and the part of the oil between the gears is squeezed out, forming the oil pressing process of the gear pump. When the gear is meshed, the tooth-direction contact line separates the oil suction cavity and the pressure oil cavity, which has an oil distribution effect.
When the driving gear of the gear pump is driven by the motor to continuously rotate, the gear teeth are disengaged from the meshing side, because the sealing volume becomes larger, the oil is continuously sucked from the oil tank, and the gear teeth enter the meshing side because the sealing volume decreases continuously. Drain oil, this is the working principle of the gear pump.
The front and rear covers of the pump and the pump body are positioned by two positioning pins 17, which are fastened with 6 screws as shown in Figure 3-3. In order to ensure that the gear can roll flexibly and at the same time to ensure minimum leakage, there should be a proper gap (axial gap) between the gear end face and the pump cover. The axial gap is 0.025~0.04mm for small flow pumps and 0.025~0.04mm for large flow pumps. 0.04~0.06mm.
The gap between the tooth top and the inner surface of the pump body (radial gap), because the sealing band is long, and the shear flow formed by the tooth top linear velocity is opposite to the direction of oil leakage, so the impact on leakage is small, which should be considered here. The problem is: when the gear is subjected to an unbalanced radial force, the tooth top should be prevented from colliding with the inner wall of the pump, so the radial gap can be slightly larger, generally 0.13~0.16mm.