A positive displacement pump is a pump that uses a change in the internal volume of a pump cylinder to deliver a liquid. Such as reciprocating pumps, rotor pumps.
Classification
Reciprocating pump:
A reciprocating pump is a pump that uses a reciprocating motion of a piston to deliver liquid. The reciprocating motion of the piston transfers energy directly in the form of static pressure energy. Since the liquid is incompressible, the liquid can be subjected to a high pressure when the piston is pumping the liquid, thereby obtaining a high lift.
Rotor pump:
The rotor pump consists of a stationary pump casing and a rotating rotor. It has no suction valve and discharge valve. The side of the pump body that is in contact with the liquid in the pump body directly applies energy to the liquid in the form of static pressure, and is squeezed by the rotating rotor. The action discharges the liquid while leaving space on the other side to form a low pressure for continuous inhalation of the liquid. The rotor pump has a high pressure head, a small flow rate and a uniform discharge. It is suitable for conveying liquids with high viscosity and lubricity but no solid particles. Types include gear pumps, screw pumps, vane pumps, flexible impeller pumps, Roots pumps, rotary piston pumps, etc. Among them, gear pumps and screw pumps are the most common rotor pumps.
The screw pump is a kind of rotor pump. Compared with the reciprocating pump, it has the following advantages: (1) It has the smoothness of the operation of the centrifugal pump, no noise (only the sound of the motor is heard), no oil leakage, no need for the oil recovery device. And auxiliary equipment such as water cooling; (2) It has the characteristics of high efficiency of volumetric pump, and the displacement is constant when the pressure changes (fixed speed); (3) less leakage point, small maintenance, low maintenance cost and short maintenance time. However, the screw pump is mainly used to transport high-viscosity oil. The efficiency of conveying thin oil is relatively low, and the outlet pressure cannot be too high. Otherwise, the internal leakage increases, which affects the safe use of the pump. At the same time, the screw pump adapts to the change of the flow rate. Pipes with large flow changes require additional equipment such as frequency converters to adjust pump flow.
