In a typical centrifugal pump, the power always increases with the increase of the flow rate, that is, the power curve is a curve that rises with the increase of the flow rate, which brings a problem to the use of the pump: when the pump is When the design operating point is running, generally, the power of the pump is less than the rated power of the motor. The use of this pump is safe; but when the pump head is reduced, the flow will increase (as can be seen from the pump performance curve).
The power also increases. When the flow rate exceeds the design condition point flow and reaches a certain value, the input power of the pump may exceed the rated power of the motor and cause the motor to be overloaded and burned. When the motor is overloaded, either the protection system acts to stop the pump from rotating; or the protection system fails to burn the motor.
The lift of the pump is lower than that of the design working point. It is often encountered in practice. In one case, when the pump is selected, the lift of the pump is too high, and in actual use, the pump is lowered. In the other case, the operating point of the pump is not well determined in use, in other words the pump flow needs to be adjusted frequently; there is also a case where the pump needs to be changed frequently. These three situations may overload the pump and affect the reliability of the pump. It can be said that the range of use of pumps (including sewage pumps) without full lift characteristics is greatly limited. The so-called full head characteristic (also known as no overload feature) means that the power curve rises very slowly with increasing flow rate.
More ideally, when the flow rate increases to a certain value, the power will not rise any more, but will have some Falling, that is to say the power curve is a curve with a hump. If so, we only need to select the power rating of the motor slightly more than the power of the hump point, then in the entire range of 0 flow to maximum flow, you are in that one When operating at the operating point, the pump power will not exceed the motor power and the pump will be overloaded. It is very convenient and reliable for the pump with this performance whether it is selected or used. In addition, the motor power does not need to be too large, which can save considerable equipment costs.
