The structure of the external meshing double gear pump. The tooth shape is a double arc sine curve, and a pair of meshing gears and pump cylinders separate the suction and discharge chambers. When the gear rotates, the inter tooth volume at the point where the teeth on the suction chamber side disengage gradually increases, the pressure decreases, and the liquid enters the inter tooth space under the pressure difference. As the gears rotate, the liquid between each tooth is carried to the discharge chamber. At this point, the volume between the teeth at the meshing point of the discharge chamber gradually decreases, and the liquid is discharged. Gear pumps are suitable for conveying lubricating liquids that do not contain solid particles, are non corrosive, and have a wide viscosity range. The flow rate of the pump can reach 300 m3/h, and the pressure can reach 3 × 107 Pa. It is commonly used as a hydraulic pump and for transporting various types of oil products. The gear pump has a simple and compact structure, easy manufacturing, convenient maintenance, and self-priming ability, but it has large flow and pressure pulsations and high noise. Gear pumps must be equipped with safety valves to prevent damage to the pump or prime mover due to reasons such as blockage of the discharge pipe causing the outlet pressure of the pump to exceed the allowable value. The opening pressure of the safety valve is generally 1.5 times the working pressure.
