Working Principles and Characteristics of Common Water Pumps

Figure 1: Electric water pump.

Water pump is a machine that transports or pressurizes liquids, which is mainly composed of impeller, pump case, pump shaft, bearing, filling seal device, and other parts. It transfers the mechanical energy or other external energy of the prime motor to the liquid to increase the energy of the liquid, mainly used to transport the liquid, including water, oil, acid and alkali solution, emulsion, suspended liquid and liquid metal, etc.

It also transports gas and liquid mixture and liquid containing suspended solids. The technical parameters of water pump performance contain flow, suction head, head, shaft power, water power, efficiency, etc., and it can be divided into positive displacement pump, vane pump and other types, according to different working principles.

Positive displacement water pump utilizes the periodic change of its working chamber volume to transfer energy, and vane pump uses the interaction between rotating blades and liquid to transfer energy, including centrifugal pump, axial flow pump and mixed flow pump.

1. Working Principle and Characteristics of Centrifugal Pump

1.1 Working Principle of Centrifugal Pump

Vane pump can be divided into: centrifugal pump, mixed flow pump, axial flow pump and vortex pump. Centrifugal pump can be divided into single-stage pump and multi-stage pump. Mixed flow pump can be divided into volute pump and guide vane pump. Axial flow pumps can be divided into fixed blades pump and adjustable blades pump. Vortex pump can be divided into single suction pump, double suction pump, self-priming pump, non self-priming pump.

1.2 Positive Displacement Pump

Figure 2: Single-stage centrifugal pump.

Before the water pump is started, fill the pump and the water inlet pipe with water. After the pump is running, the water in the impeller passage, under the action of centrifugal force generated by the high-speed rotation of the impeller, is thrown around and pressed into the volute, and vacuum is formed at the inlet of impeller. The water in the pool is sucked along the suction pipe under the external atmospheric pressure to supplement this space. Then the water sucked in is thrown out by the impeller and enters the outlet pipe through the volute.

Thus, if the centrifugal pump impeller rotates continuously, it can continuously suck and press water, and the water can be continuously lifted from low to high or far away. To sum up, the reason why it is given the name of centrifugal pump is that it lifts the water to a high place under the action of the centrifugal force generated by the high-speed rotation of the impeller.

1.2 General Characteristics of Centrifugal Pump

Figure 3: Multiple-stage centrifugal pump.

The water flowing in the centrifugal pump is sucked in along the axial direction of the impeller, and flows out perpendicular to the axial direction, that is, the direction of the inflow direction is vertical to outflow direction.

Since the centrifugal pump sucks water in a vacuum through the inlet of the impeller, it is necessary to inject water into the pump and the suction pipe before starting, or use a vacuum pump to extract the air to form a vacuum. Moreover, the pump case and the suction pipe must be strictly sealed without air leakage, otherwise it will not form a vacuum, neither be able to suck water.

Since it is impossible to form absolute vacuum at the impeller inlet, the suction height of the centrifugal pump cannot exceed 10 meters. In addition, the actual allowable installation height (the height between the pump axis and the sucked water surface) is far less than 10 meters due to the loss along the suction pipeline. If the installation is too high, it will not suck water; besides, since the atmospheric pressure in mountainous areas is lower than that in plain areas, the installation height of the same water pump should be reduced when it is installed in mountainous areas, especially in high mountainous areas, otherwise it cannot suck water.

2. Working Principle and Characteristics of Axial Flow Pump

2.1 Working Principle of Axial Flow Pump

Figure 4: Axial flow pump.

Different from the working principle of centrifugal pump, the axial flow pump mainly utilizes thrust generated by high-speed rotation of impeller to lift water. The lifting force generated by the rotating blades of the axial flow pump on the water can push the water from the bottom to the top.

The blades of axial flow pump are usually submerged into the pool where water is sucked. Due to high-speed rotation of impeller, Due to the high-speed rotation of the impeller, the water is continuously pushed upward by the lifting force generated by the blades, so that the water flows out along the outlet pipe. Constant rotation of impeller comes to push the water at the top position.

2.2 General Characteristics of Axial Flow Pump

Water flowing in the axial flow pump is sucked along the axial direction of impeller, and flows out along the axial direction, thus called axial flow pump.

It has the characteristics of low head (ranging from 1 meter to 13 meters), large amount of flow, high benefits, suitable for drainage and irrigation in plains, lakes and rivers. Watering is not required before starting, and the operation is simple.

3. Working Principle and Characteristics of Mixed Flow Pump

Figure 5: Mixed flow pump.

3.1 Working Principle of Mixed Flow Pump

As the shape of impeller of mixed flow pump is between impeller of centrifugal pump and impeller of axial flow pump, working principle of mixed flow pump is mixed centrifugal force with lifting force. It is under the two comprehensive forces that water flows out of the impeller at a certain angle with shaft, and is lifted at the top through volute chamber and pipeline.

3.2 General Characteristics of Mixed Flow Pump

Compared with centrifugal pump, mixed flow pump has lower head and larger amount of flow. Compared with axial flow pump, it has higher head and less amount of flow. It is suitable for drainage and irrigation in plain and lake areas.

Water flowing in the mixed flow pump is sucked in and flows out at a certain angle with the impeller shaft, called diagonal flow pump as well.

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