Abstract: The correct selection and use of fan and pump are the important prerequisite for raising their efficiency. Taking fan as the example the similar operation relations of fan and pump are explained, the essential conditions which must be satisfied for similarity of fan and pump were proposed, and the inevitable results of the similarity were given. The variable frequency speed regulation has become the first scheme to be selected. According to the similarity law of fan and pump, in the process of reducing speed, the efficiency of the fan and pump will be kept at the same value, and its flow rate, pressure(or delivery head) and power are reduced in proportion to speed, speed square and speed cube respectively.

Key words: Fan, pump, energy saving, fan characteristic curve, operating point, variable frequency speed regulation, frequency transformer