In general centrifugal pumps, the power always increases with the increase of flow, that is, the power curve is a curve that increases with the increase of flow, which will bring a problem to the use of pumps:
1. When the pump operates at the design operating point, generally speaking, the power of the pump is less than the rated power of the motor, and the use of this pump is safe; However, when the pump head decreases, the flow will increase (as can be seen from the pump performance curve) and the power will increase.
2. When the flow exceeds the flow at the design operating point and reaches a certain value, the input power of the pump may exceed the rated power of the motor, resulting in motor overload and burning. When the motor is overloaded, either the protection system acts to stop the pump; Or the protection system fails to burn the motor.
3. It is often encountered in practice that the pump head is lower than the design working point. One case is that the pump head is too high in pump selection, but the pump is used with lower head in actual use; Another situation is that the operating point of the pump is not easy to determine in use. In other words, the flow of the pump needs to be adjusted frequently; There is another situation where pumps need to be changed frequently
These three situations may overload the pump and affect the service reliability of the pump. It can be said that the use range of pumps without full head characteristics (including sewage pumps) will be limited to a great extent.
The so-called full head characteristic (also known as no overload characteristic) means that the power curve rises very slowly with the increase of flow. More ideally, when the flow increases to a certain value, the power will not rise again, but will decrease. That is to say, the power curve is a curve with hump. If so, we only need to select the motor rated power slightly exceeding the power value at the hump point, Then, in the whole range from 0 flow to maximum flow, no matter which operating point you operate at, the pump power will not exceed the motor power and overload the pump. For the pump with this performance, it will be very convenient and reliable both in selection and use.
In addition, the motor power does not need to be too large, which can save considerable equipment cost.
The drainage pumps used in the building include submersible sewage pump, underwater drainage pump, vertical sewage pump and horizontal sewage pump. As the general site in the building is small and the drainage volume is small, the submersible sewage pump and submerged sewage pump can be preferred, of which the submerged sewage pump is generally used in important places; Vertical sewage pump and horizontal sewage pump are required to be equipped with isolation foundation, self filling water absorption and occupy a certain site, so they are rarely used in buildings.
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