What is Gear Pump?

Gear Pump Introduction

Gear pump is a rotary pump that depends on the working volume change and movement formed between the pump cylinder and the meshing gear to transport the liquid or make it pressurized, which belongs to the hydraulic parts. Composed of two gears, the pump body and the front and back cover of two closed Spaces, when the gear rotates, the volume of the space on the side of the gear off from small to large, forming a vacuum, the liquid suction, the volume of the space on the side of the gear mesh from large to small, and the liquid into the pipeline. The suction cavity and the discharge cavity are separated by the meshing line of two gears. The outlet pressure of the gear pump depends entirely on the size of the resistance at the pump outlet.

Working Principle

The concept of gear pump is very simple, its most basic form is two of the same size gear in a closely matched shell meshing rotation, the interior of the shell similar to the "8" figure, two gears installed inside, the outer diameter of the gear and the two sides of the shell closely matched. The material from the extruder enters between the two gears at the suction inlet and fills this space, moving along the housing as the teeth rotate and finally discharging when the two teeth engage.

In terms of terminology, gear pump is also called positive displacement device, that is, like a cylinder cylinder piston, when a tooth into the fluid space of another tooth, because the liquid is incompressible, so the liquid and the tooth can not occupy the same space at the same time, so that the liquid is mechanically squeezed out. Because of the continuous engagement of the teeth, this phenomenon occurs continuously, and thus provides a continuous discharge at the pump outlet, with the same amount of discharge at each turn of the pump. With the continuous rotation of the drive shaft, the pump continues to discharge fluid. Pump flow is directly related to pump speed.

In fact, there is a very small amount of fluid loss in the pump, because these fluids are used to lubricate both sides of the bearing and gear, and the pump body can never be without clearance, so the fluid can not be 100% discharged from the outlet, so a small amount of fluid loss is inevitable, which makes the pump operating efficiency can not reach 100%. However, the pump can still operate well, for most extruded materials, can still reach 93% ~ 98% efficiency.

Driving Device

The gear pump is driven by an independent motor, which can effectively block the upstream pressure pulsation and flow fluctuation. The pressure pulsation at the outlet of the gear pump can be controlled within 1%. The use of a gear pump in the extrusion line can improve the flow output speed, reduce the material in the extruder shear and dwell time.

External gear pump is the most widely used gear pump, the general gear pump usually refers to the external gear pump. Its structure, as shown in Figure 1, is mainly composed of driving gear, driven gear, pump body, pump cover and safety valve. Pump body, pump cover and gear constitute the sealing space is the gear pump studio. The shaft of the two gears is respectively installed in the bearing holes on the two pump covers. The driving gear shaft extends out of the pump body and is driven by the motor to rotate. External gear pump has the advantages of simple structure, light weight, low cost, reliable operation and wide application range.

When the gear pump works, the driving wheel rotates with the motor and drives the driven wheel to rotate. When the meshing teeth on one side of the suction chamber are gradually separated, the volume of the suction chamber increases, the pressure decreases, and the liquid in the suction tube is sucked into the pump; The suction liquid is pushed to the discharge chamber by the gear in two ways in the tooth groove. After the liquid enters the discharge chamber, because the teeth of the two gears constantly mesh, the liquid is squeezed from the discharge chamber into the discharge pipe. The driving gear and driven gear keep rotating, the pump can continuously suction and discharge liquid.

The pump body is equipped with a safety valve, when the discharge pressure exceeds the specified pressure, the conveying liquid can automatically open the safety valve, the high pressure liquid back suction pipe.

Internal gear pump, it is composed of a pair of internal gear meshing each other and their middle crescent shaped parts, pump shell, etc. The function of the crescent piece is to separate the suction chamber from the discharge chamber. When the driving gear rotates, the local vacuum is formed at the place where the gear engages. The liquid is sucked into the pump and filled with the suction chamber teeth, and then enters the discharge chamber along the inner and outer sides of the crescent piece. At the point where the teeth engage, the liquid that exists between the teeth is squeezed into the discharge tube.

Gear pump in addition to self-priming capacity, flow and discharge pressure has nothing to do with other characteristics, no suction valve and discharge valve on the pump shell, with simple structure, uniform flow, reliable work characteristics, but low efficiency, noise and vibration, easy to wear, mainly used to transport non-corrosive, no solid particles and lubricating ability of various oils, the temperature is generally not more than 70 ℃, Such as lubricating oil, edible vegetable oil, etc. The general flow range is 0.045-30ms /h, the pressure range is 0.7-20mpa, and the working speed is 1200-4000r /min.