Multistage pumps are mainly used for high temperature condensate recovery, boiler feed water, and also for water supply and drainage in factories, cities and mines.

The composition of the multistage pump

The multistage pump is mainly composed of four parts: stator, rotor, bearing and shaft seal:

1. The stator part of the multi-stage pump is mainly composed of a suction section, a middle section, a discharge section and a guide vane, etc. There are tension bolts to clamp each section to form a working room. D-type pumps generally inhale horizontally and spit vertically upwards; when used for water injection in oil fields, the inlet and outlet of the pump are vertically upwards. The outlet and inlet of the DG type multistage pump are vertically upward.

1. The rotor part of the multistage pump is mainly composed of shaft, impeller, balance disc and shaft sleeve. The axial force is balanced by the balance disc.

1. The multi-stage pump bearing is mainly composed of bearing body, bearing and bearing gland, etc. The bearing is lubricated with grease or thin oil.

1. The shaft seal of the multi-stage pump is sealed with soft packing, which is mainly composed of the sealing body, packing and water retaining ring on the water inlet section and the tail cover. D-type pump water seal water comes from the pressure water in the pump. DG type pump seal water comes from external water supply.

1. Multi-stage pump rotation The pump is directly driven by the prime mover through the elastic coupling. When looking at the pump from the prime mover side, the pump rotates clockwise. D and DG pumps are horizontal single-suction multi-stage segmental centrifugal pumps. For conveying clean water (with impurity content less than 1%, particle size less than 0.1mm) or other liquids with physical and chemical properties similar to water. The temperature of the medium conveyed by the D-type pump is less than 80 ℃, and it is suitable for mine drainage, oil field water injection, factory and urban water supply and drainage and other occasions. Oilfield injection pumps use different materials according to the corrosiveness of the medium. DG type pump conveying medium temperature is less than 105 ℃, suitable for various boiler feed water.

Working principle of multistage pump

The multistage pump is a type of centrifugal pump, and it also relies on the rotation of the impeller to obtain centrifugal force. When the gas density reaches the working range of the mechanical vacuum pump, it is pumped out, to gradually obtain a high vacuum.

An appropriate amount of water is installed in the multistage pump body as the working fluid. When the impeller rotates clockwise, the water is thrown around by the impeller. Due to the centrifugal force, the water forms a closed ring of approximately equal thickness determined by the shape of the pump cavity. The inner surface of the lower part of the water ring is just tangent to the impeller hub, and the upper inner surface of the water ring is just in contact with the tip of the blade (in fact, the blade has a certain insertion depth in the water ring). At this time, a crescent-shaped space is formed between the impeller hub and the water ring, and this space is divided into several small cavities equal to the number of blades by the impeller.

If the bottom 0° of the impeller is taken as the starting point, the volume of the small cavity changes from small to large when the impeller rotates 180 degrees before, and it communicates with the suction port on the end face. At this time, the gas is inhaled, and when the suction ends, the small cavity is isolated from the suction port; when the impeller continues to rotate, the small cavity becomes smaller, so that the gas is compressed; when the small cavity is communicated with the exhaust port, the gas is discharged out of the pump.

To sum up

The multi-stage pump realizes suction, compression and exhaust by the change of the volume of the pump cavity, so it is a centrifugal pump with variable volume.

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