Centrifugal pumps are widely used in the industry. It employs centrifugal motion to transfer liquid from one place to the other. Most of water supply systems use this kind of pumps as well. This chapter will give some basic introduction of centrifugal pumps.When a specific flow rate is selected for a system, pipeline resistance curve shows the relationship between head and flow rate with a certain discharge valve opening.
Pipeline resistance characteristic identifies the total head that must be overcome due to water level and pressure difference and the resistance of liquid flow in the pipeline. Pipeline resistance characteristic depends on length of pipe, size of pipe, etc. As shown in Figure 2, a flow rate increase will lead to a head increase. Changing the discharge valve opening will change the water supply capacity under a certain head. Therefore, pipeline resistance characteristic reflects the relationship between the Head and flow rate of water supply.
The intersection point (A) of the two curves is natural working point. Point A satisfies both the head characteristic and the pipeline resistance characteristic. That is that the water supply and the water demand are same. Pump pressure matches system losses. The water supply system runs in steady state.There are six major parts in a centrifugal pump. They are seal, shaft, casing, impeller, bearing and coupling.
Seal can be pack rings or mechanical seal which prevents water leakage and air getting in to keep internal vacuum of the case.
Shaft connects a motor via a coupling. It transmit the output torque of the motor to the impeller during operation.
Casing, housing the internal parts and mounting the pump body, acts as a pressure containment vessel. Water is absorbed into the case and accelerated to a high velocity.
Impeller, the core part of a centrifugal pump, revolves at high speed and develops centrifugal force to increases water pressure.
Bearings, supporting the weight of the shaft assembly and aligning the pump shaft to the motor shaft.
Coupling, connecting the pump shaft and the motor shaft, transmits the motor output torque to the impeller.