The performance of the pump includes the flow, the lift, the power and so on. An important indicator of the performance of the pump is the efficiency of the pump &eta.
In the type: N is the effective power of the pump, the output power, the W; the N is the shaft power of the pump, that is, the input power, W.
The key to the efficiency of the pump is the power loss, including the mechanical loss, the volume loss and the hydraulic loss. However, because the flow of liquid in the pump is more complex so far, these power can not be accurately calculated from the theory.
Mechanical loss
The pump needed from 3 parts: when the loss of high rotation speed, friction loss of bearings and bushings. This part of the loss accounts for about 1% of the energy loss. The impeller of the centrifugal pump rotation speed on the liquid filled in the pump and the mechanical energy generated is not all to the liquid through the impeller, the impeller friction plate before and after consumption and liquid and liquid friction and the surface of the cover plate and the pump cavity generated in a part of the friction loss. The local friction loss between the balance disc and balance in the rotation process generated. The friction loss of this part of the disc is about 5% of the energy loss, and the mechanical efficiency is small in mechanical efficiency η m indicates:
In the type: N is the power of mechanical loss, W. The main cause of mechanical loss is the quality of manufacturing, and the friction loss of the bearing is small and negligible.
In the quality of the bushing and packing, if the material is not wearable and the surface is rough. The friction coefficient is large, and if the filler quality is not good, the pressure of the packing gland of the assembly is too tight, which increases the friction loss and increases the shaft power, which directly affects the efficiency of the pump. The friction loss of the disc is mainly concentrated on the front and rear cover plates and the pump chamber of the impeller, and the size depends on the surface finish of the component. Because the liquid itself has the viscosity, when the liquid flow surface is not smooth, it is necessary to increase the friction resistance, so that the efficiency of the pump is directly affected.
The volume loss is a direct effect on the flow loss of the pump. The flow volume of impeller (QY) is not completely transported to the pump outlet. Due to the pressure difference, a part of the liquid energy gained from the pump cavity through impeller is consumed in the leakage process. This is part of the gap leakage Q, which increases with the increase of the friction gap of the seal ring. There is also an interstage leakage for the multistage pump, and the expansion of the friction gap of the seal ring is an important reason for the decrease of the pump efficiency. The other part is the leakage of the balance mechanism. Because there is pressure difference on both sides of the balance mechanism, a part of the liquid will naturally leak from the high pressure area to the low pressure. The leakage is the volume loss, and the volume loss is calculated by the volume efficiency (&eta).
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