Mistakes in the use of centrifugal pump

 

1. Use high lift pump to pump water to low head

A lot of operators think the lower the pump lift, the less the load of motor, so they always purchase high lift pump. That’s misunderstanding. In fact, for centrifugal pump, when the model of the pump is decided, its power consumption is proportional to the actual flow of the pump. The flow of the pump will decrease when its lift accelerates. Therefore, higher lift causes smaller flow, consumes much more power, while lower lift causes larger flow, consumes much less power. In order to prevent motor overload, the actual lift of the pump at work is generally required not to be less than 60% of the calibrated lift. So when you use a high lift pump to deliver water to lower height, the motor is easy to get overload and hot or even be burned out.

If you have to do that in emergency, a valve that can adjust water flow must be installed on the water outlet pipe to reduce flow and prevent motor overload, or block the water outlet to some degree with a piece of wood or something. Note the temperature of the motor. Once it is too hot, reduce the flow in outlet or power off the pump timely. This is another that is apt to be misunderstood. Some operators may think if we block the water outlet to reduce flow, the motor load will accelerate. But in fact, all standard high power centrifugal pump drainage and irrigation machinery units have valves installed on their water outlet pipes. That’s why in order to reduce the load of the motor, they close the valve in the beginning, and then gradually open it after the motor is started.

2.Connect thin pipes to large diameter pumps

A lot of operators think the practical lift can be increased in this way. In fact, the actual pump lift = total lift - loss lift. For a certain model of pump, the total lift is fixed. The lift loss is mainly caused by resistance in the pipes. Obviously, the thinner pipe will cause stronger resistance and more loss of lift. In this way, when you use thin pipe, the actual lift of the pump will not be increased, but will be decreased. As a result, the efficiency of the pump will be decreased.  

Similarly, if you connect a wide pipe with a pump of small diameter, the actual lift of the pump will not be decreased, but be increased because the resistance of pipe is reduced and lift loss is reduced. Some operators may think if you connect a wide pipe with a pump of small diameter, the motor load will surely accelerate greatly. In their minds, when the diameter of the pipe is increased, the water in outlet pipe will generate much more pressure on impellers, so the motor will bear much more load. But in fact, the pressure of fluids is only related with lift, not with the diameter of pipe. Once the lift is fixed, and the size of impellers of the pump is fixed, whatever the diameter of the pipe is, the pressure of fluids on impellers will not change. If the pipe has larger diameter, the water in it will feel less resistance, and the flow will increase, which will consume a little more power. But as long as it is within the range of regulated lift, the pump can always work normally however the pipe diameter is increased. Besides, this can also reduce pump loss, increase pump efficiency.

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