Working principle and operation maintenance of gear pumps

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Gear pump: A rotary pump that transports liquids or increases their pressure by utilizing the changes and movements in the working volume formed between the pump cylinder and the meshing gears. 　　Structure of an external gear double gear pump. A pair of intermeshing gears and a pump cylinder separate the suction chamber from the discharge chamber. As the gear rotates, the volume between the teeth where they are separated on the suction chamber side gradually increases, resulting in a decrease in pressure; the liquid then enters the space between the teeth due to this pressure difference. As the gear rotates, the liquid between the teeth is carried to the discharge chamber. At this point, the inter-tooth volume at the gear mesh on the discharge chamber side gradually decreases, thereby discharging the liquid. Gear pumps are suitable for transporting lubricating fluids that contain no solid particles, are non-corrosive, and have a wide viscosity range. The pump can achieve a flow rate of up to 300 m3/h and a pressure of up to 3×107 Pa. It is commonly used as hydraulic pumps and for transporting various types of oils. Gear pumps have a simple and compact structure, are easy to manufacture and maintain, and possess self-priming capability; however, they experience large flow and pressure fluctuations as well as high noise levels. A gear pump must be equipped with a safety valve to prevent the pump or the driving motor from being damaged due to the outlet pressure exceeding acceptable levels, which can occur as a result of factors such as a blocked discharge pipe. (1) Working principle: A gear pump is a type of positive displacement pump; it consists of two gears, a pump body, and front and rear covers that create two enclosed spaces. As the gears rotate, the volume of the space on the side where the gears are separated decreases, creating a vacuum that draws in liquid. Meanwhile, the volume of the space on the side where the gears are in contact increases, forcing the liquid into the pipeline. The suction chamber and the discharge chamber are separated by the meshing line of two gears. 　　The pressure at the outlet of a gear pump depends entirely on the magnitude of the resistance at the pump outlet. 　　(II) Operation and Maintenance 　　1. Starting: 　　(1) Check the sealing integrity of all pipeline flanges and joints before starting. 　　(2) Rotate the coupling; there should be no sound of friction or collision. 　　(3) When starting for the first time, the pump should be filled with the fluid to be transported. 　　(4) Before starting, the valves in the suction and discharge pipelines should be fully opened; it is strictly prohibited to start with the valves closed. 　　(5) After verifying the motor’s rotation direction, start the motor. 　　2. Parking: (1) Turn off the motor. 　　(2) Close the inlet and outlet valves of the pump.