Marine centrifugal pumps are the most used marine pump in ship, especially for auxialiary machinery, like seawater cooling pump, daily water service pump, fire fighting pump…
Working principle
the main components of a marine centrifugal pump are casing and impellers. The spiral casing is also called volute, which includes volute chamber and diffuser. A typical centrifugal pump has one or more shaft-mounted vane impellers that rotate within a stationary casing and transfer energy to the fluid flowing between their vanes.
When a marine centrifugal pump is working, liquid filled in the pump will rotate with impellers, and the liquid will move to the periphery of the impeller due to the centrifugal force. So there is a vacuum in the eye of the impeller, and more liquid will enter into the pump under the pressure of liquid surface. When liquid is discharged from the impeller its pressure and velocity is increased considerably. Then the liquid will be collected by the volute chamber and guided to diffuser. The cross section area of diffuser increases gradually, so the velocity of the liquid will decrease and most of kinetic energy will be converted into pressure energy. As the impellers keep rotating, liquid can be drawn and discharged continuously.
Characteristics
(1)The advantages of marine centrifugal pump are in the following:
①Flow rate is continuous, even and can be adjusted easily. The pump can work steadily with wide range of flow rate.
②Running speed is high and the pump can be connected with prime motor directly. The configuration is compact, as well as smaller size, less weight and lower price compared with reciprocating pump with the same capacity.
③With less easily damaged components, the pump can be used to deliver dirty liquid.
(2)The disadvantages of marine centrifugal pump are as following:
①No self-priming ability.
②Its flow rate varies with head. Generally speaking, the higher working head is, the smaller flow rate. For example, when the head reaches the shut-off head, the pump doesn’t deliver any liquid.
③Head developed by the pump is determined by the diameter of impeller and running speed. Thus centrifugal pump is not suitable for liquid delivery under high head and small flow rate. This requires long and narrow flow channel of impeller which is hard to be manufactured. In addition, efficiency is low under this working condition.
