When we select the horizontal multistage centrifugal pump, we must first know what are the main performance parameters of the horizontal multistage centrifugal pump, and what do these parameters represent? After determining the performance parameters of the centrifugal pump, you can accurately select the centrifugal pump that suits you. The main performance parameters of the horizontal multistage centrifugal pump are as follows:
1, flow
The flow rate of a centrifugal pump refers to the volume of liquid discharged into the pipeline system per unit time. It is generally expressed by Q, and the common units are l/s, m3/s or m3/h. The flow rate of a centrifugal pump is related to the structure, size and speed of the pump. The flow rate of the pump depends on the structural size of the pump (mainly the diameter of the impeller and the width of the blade) and the speed. During operation, the amount of liquid that the pump can actually deliver is also related to the resistance of the pipeline and the required pressure.
2, head
The pressure head of the centrifugal pump refers to the effective energy supplied by the centrifugal pump to the unit weight (1N) of the liquid. It is generally expressed by H, and the unit is J/N or m. The head of a centrifugal pump is also called the head of the pump. The head of the pump depends on the structure of the pump (such as the diameter of the impeller, the bending of the blades, etc., and the speed. At present, the head of the pump cannot be theoretically accurate. Calculations are generally determined by experimental methods.
3, efficiency
In the process of pumping liquid, the shaft power is greater than the power obtained from the impeller by the liquid discharged to the pipeline, because volume loss, hydraulic loss and mechanical loss will consume a part of the power, and the efficiency of the centrifugal pump reflects the pump The degree of energy utilization.
The efficiency value of the pump is related to the pump type, size, structure, manufacturing accuracy and the nature of the liquid to be transported. Large pumps have higher efficiency values, and small pumps have lower efficiency values.
The energy loss of the centrifugal pump includes the following three items:
(1) The loss of hydraulic power is the loss of energy due to the flow resistance of the liquid flowing through the blades and volutes, the local resistance of the flow channel area and direction changes, and the circulation and vortices in the impeller channel. This loss can be reflected by the hydraulic efficiency ηh. Under the rated flow, the direction of movement of the liquid is exactly the same as the inlet angle of the blade. At this time, the loss is the smallest and the hydraulic efficiency is the highest, and its value is in the range of 0.8 to 0.9.
(2) Mechanical efficiency Loss of energy due to the friction between the surface of the impeller rotating at high speed and the liquid, and the mechanical friction of the pump shaft at the bearing, shaft seal, etc. Mechanical loss can be reflected by the mechanical efficiency ηm, which is between 0.96 and 0.99.
(3) Volume loss is the loss caused by leakage. The ratio of the pump power when there is no volume loss to the pump power when there is volume loss is called the volumetric efficiency ηv. The volumetric efficiency value of the closed impeller is between 0.85 and 0.95.
The total efficiency of the centrifugal pump consists of three parts, namely
Η=ηvηhηm(2-14)
The efficiency of a centrifugal pump is related to factors such as pump type, size, processing accuracy, liquid flow and properties. Generally, the efficiency of small pumps is 50 to 70%, while that of large pumps can reach 90%.
4, shaft power N
The power input by the motor into the pump shaft is called the shaft power of the pump, and the unit is W or kW. The effective power of a centrifugal pump refers to the energy obtained by the liquid from the impeller in a unit time.
Ne=HgQρ(2-15) where
Ne------The effective power of the centrifugal pump, W;
H--------The effective pressure head of the centrifugal pump, m;
Q--------The actual flow rate of the centrifugal pump, m3/s.
Due to the above three energy loss in the pump, the shaft power must be greater than the effective power, namely
