The main features of the positive displacement pump are as follows:
1The flow of a given pump at a certain speed or number of reciprocations is constant and hardly changes with pressure. Operating point pressure and shaft power depend on the condition of the device system connected to the pump, so when the pump is operating in the absence of the discharge line (corresponding to an infinite system resistance), its pressure and shaft power will increase to the point that the pump Or the prime mover is damaged, so a safety valve must be provided to protect the pump (except for steam direct action or compressed air driven pumps).
2 The flow and pressure of the reciprocating pump have a large pulsation, and corresponding pulsation measures need to be taken; the oscillating pump generally has no pulsation or only a small pulsation.
3 has self-priming ability, the pump can start to pump the air in the suction liquid.
4 When starting the pump, the discharge line valve must be fully opened.
5 The reciprocating pump is a low-speed machine, large in size, and expensive in manufacturing and installation; the rotary pump has a high speed and can reach 3000 rpm.
6 Reciprocating pumps for high pressure (up to 350 MPa) and small flow (100 m3/hr or less); rotary pumps for medium and small flow (below 400 m3/hr) and higher pressure (35 MPa below ). In general, the positive displacement pump has higher efficiency than the power type pump, and the efficiency curve has a wider effective area. The efficiency of the reciprocating pump is generally 70 to 85%, and high to 90%.
7 The reciprocating pump is suitable for conveying clean liquid or gas-liquid mixture. Some pumps such as a diaphragm pump can transport mud, sewage, etc., and are mainly used for water supply, high pressure liquid source, and metering and transportation. The rotary pump is suitable for delivering a lubricious clean liquid and liquid gas mixture, especially a highly viscous liquid, which is mainly used for the transportation of oil products, food liquids and hydraulic transmission.