Working principle of vacuum pump group

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The vacuum pump unit plays an important role in the condensing steam turbine unit. Before start-up, the vacuum pump group draws the gas in the condenser to establish the vacuum. During the start-up and operation, the vacuum pump group pumps the non-condensable gas leaked or carried by the working medium into the condenser to enhance the condensation effect of the steam. The water ring vacuum pump unit has the characteristics of simple structure, economical operation and wide application range.

The vacuum pump unit plays an important role in the condensing steam turbine unit. Before start-up, the vacuum pump group draws the gas in the condenser to establish the vacuum. During the start-up and operation, the vacuum pump group pumps the non-condensable gas leaked or carried by the working medium into the condenser to enhance the condensation effect of the steam. The water ring vacuum pump unit has the characteristics of simple structure, economical operation and wide application range.

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1. working principle and structure

The water ring vacuum pump unit is composed of impeller, pump body, suction exhaust port, auxiliary pipeline, etc. The impeller is eccentrically mounted in the pump body. When the impeller rotates, under the action of centrifugal force, the water is thrown around, forming a closed water ring similar to the shape of the pump chamber. The outer surface of the water ring is in contact with the pump cavity, and the inner surface is in contact with the vane. Several crescent-shaped cavities are formed between the impeller hub and the water ring. When the impeller rotates clockwise, due to the eccentric arrangement, the volume of a single small cavity increases from small to large, and the pressure in the cavity decreases continuously. When the pressure is lower than the pressure of the gas in the pumping container, the gas enters the small cavity from the suction port, which is the process of suction.

As the impeller continues to rotate, the volume of the small cavity gradually decreases, and the pressure increases until the gas pressure is greater than the exhaust pressure, and the compressed gas is discharged from the exhaust port. In this way, during the continuous operation of the pump, the gas is continuously sucked and discharged along the axial direction of the impeller, so as to achieve the purpose of continuous extraction of steam.

2. improvement measures

When the water ring vacuum pump group is running, there are problems such as operating noise and impeller cavitation. It is generally believed that the inlet pressure of the vacuum pump group is too low (lower than the saturation pressure of the working fluid), which leads to the gasification of the working water in the pump body. The specially designed cavitation protection tube leads all the air from the exhaust port to the high vacuum chamber in the pump to prevent cavitation. At the same time, a gas protective film is formed on the surface of the impeller to prevent damage to the impeller when cavitation occurs. The atmospheric ejector is a reduced-ratio nozzle, and its design conditions are supersonic.-Sonic.-Subsonic. Under adiabatic conditions, the change in fluid pressure is inversely proportional to the change in flow rate. In the case of constant outlet pressure, the scaling nozzle can obtain a lower inlet pressure. Three pneumatic valves cooperate with the atmospheric injector. In the initial stage, valves 1 and 2 are opened, valve 3 is closed, and the vacuum pump group draws gas from the condenser to establish a vacuum. When the vacuum degree reaches a high value, the valve 2 is closed, the valve 3 is opened, and the outside air flows into the atmospheric ejector at a high speed under the action of the pressure difference, and forms a supersonic airflow together with the high-speed airflow from the condenser at the inlet, and finally flows through the zoom nozzle, Enter the vacuum pump group.


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