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Talking about the subtle difference between centrifugal pumps and self-priming pumps

by:Mayer     2021-08-16
Many users don’t know the difference between self-priming pumps and centrifugal pumps. In fact, self-priming pumps are also a type of centrifugal pumps, but self-priming pumps have a higher body height and have a certain water storage capacity, so there is no need to install a bottom valve in the suction pipe. A centrifugal pump product that can suck up water after the first irrigation, so the self-priming pump can also be called a centrifugal pump according to its function, it can also be called a self-priming centrifugal pump. The main reason is that the inlet pipe of the self-priming pump does not need to be installed with a bottom valve, and the water can be sucked up after being filled with water for the first time, and there is no need to add water in the future. The pump body is larger than a centrifugal pump, and many have a water storage function. The water diversion has the function of self-priming for life, and the centrifugal pump plays the role of pressurization. The liquid level must be higher than the pump, and it can only start if it can flow into the pump body. If the liquid level is lower than the centrifugal pump, it can only be at the suction port of the inlet pipe. Install a bottom valve to fill the pump and pipeline with liquid to achieve the self-priming function, or install a water diversion tube at the inlet, such as a centrifugal pump that does not work for a long time. The water in the inlet pipeline and the pump body is basically the same when the pump is started for the second time. It is no longer necessary to fill the water again. The operation is more troublesome, because the centrifugal pump inlet bottom valve seal cannot achieve the complete sealing effect if the centrifugal pump has not been used for a long time. In addition, self-priming pumps are more effective than centrifugal pumps. Self-priming centrifugal pumps all adopt the pump body structure with axial liquid return. The centrifugal pump body is composed of a suction chamber, a liquid storage chamber, a scroll chamber, a liquid return hole, a gas-liquid separation chamber, etc. After the centrifugal pump is started normally, the impeller sucks the liquid stored in the suction chamber and the air in the suction pipe together, and The impeller is completely mixed. Under the action of centrifugal force, the liquid entrains the gas to flow to the outer edge of the scroll, forming a certain thickness of white foam belt and high-speed rotating liquid ring on the outer edge of the impeller. The gas-liquid mixture enters the gas separation chamber through the diffuser. At this time, due to the sudden decrease of the flow rate, the lighter gas is separated from the mixed liquid, and the gas continues to rise and be discharged through the outlet of the pump body. The degassed liquid returns to the liquid storage chamber, and enters the impeller again through the return hole, and mixes with the gas sucked from the suction pipe inside the impeller again, and flows to the outer edge of the impeller under the action of the high-speed rotating impeller. As this process goes on again and again, the air in the suction pipe is continuously reduced, until the air is exhausted, the self-priming pump completes the self-priming process, and the centrifugal pump is put into normal operation. Because the centrifugal pump has this unique exhaust ability, the self-priming pump can transport liquids containing gas, without installing a bottom valve, and has a good stripping function when used on a cruise ship. A cooling chamber is provided at the bottom of the bearing body of some centrifugal pumps. When bearing heating causes the temperature of the bearing body to rise more than 70℃, a cooling liquid pipe joint can be used at the cooling chamber to inject cooling liquid such as IH chemical pump. The internal sealing mechanism of the centrifugal pump to prevent the liquid from leaking from the high-pressure zone to the low-pressure zone is the front and rear seal rings. The front seal ring is installed on the pump body, and the rear seal ring is installed on the bearing body. And when it affects the efficiency and self-priming performance of the pump, it should be replaced. Centrifugal pumps are generally driven by electric motors. Before starting the pump, the pump body and suction pipeline are filled with liquid. When the impeller rotates at high speed, the impeller drives the liquid between the blades to rotate together. Due to the centrifugal force, the liquid is thrown from the center of the impeller to the outer edge of the impeller (the flow rate can be increased to 15-25m/s), and the kinetic energy also increases. When the liquid enters the pump casing, as the flow channel in the volute-shaped pump casing gradually expands, the flow rate of the liquid gradually decreases, and part of the kinetic energy is converted into static pressure energy, so the liquid flows out along the discharge port at a higher pressure. At the same time, a certain vacuum is formed at the center of the impeller due to the liquid being thrown out, and the pressure Pa at the liquid level is higher than that at the center of the impeller. Therefore, the liquid sucked into the pipeline enters the pump under the action of the pressure difference. The impeller keeps rotating, and the liquid is continuously sucked and pressed out. Because centrifugal pumps can transport liquids, they mainly rely on centrifugal force, so they are called centrifugal pumps.
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