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The difference between self-priming pump and centrifugal pump

2019-08-21
 The difference between self-priming pump and centrifugal pump

1. Mainly the self-priming pump inlet pipe does not need to install the bottom valve. After the first filling of the water, the water can be sucked up. After that, there is no need to add water. The pump body is larger than the centrifugal pump, and many of them have water storage function. It has the function of self-priming for one life of water diversion, and the centrifugal pump plays the role of supercharging. The liquid level must be higher than the pump, and it can flow to the inside of the pump body to start. If the liquid level is lower than the centrifugal pump, it can only be in the inlet pipe. Install the bottom valve in the suction port to fill the pump and the pipe with liquid to achieve the self-priming function, or install the water inlet cylinder at the inlet, such as the centrifugal pump that does not work for a long time, and the inlet pipe and the pump body during the second start. The water is basically gone, and it has to be re-irrigated once, which is more troublesome to operate. Because the centrifugal valve inlet valve seal that is not used for a long time can not achieve the effect of complete sealing, the liquid will slowly leak back to the pool, so the self-priming function is needed. The self-priming pump works better than the centrifugal pump.
2. The self-priming centrifugal pump adopts the pump body structure with axial returning. 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 normally started, the impeller sucks the liquid stored in the suction chamber together with the air in the suction tube, and The impeller is completely mixed. Under the action of centrifugal force, the liquid entrains this gas to flow to the outer edge of the wrap, and a white foam band of a certain thickness and a high-speed rotating liquid ring are formed on the outer edge of the impeller. The gas-liquid mixture enters the gas separation chamber through the diffusion tube. At this time, since the flow rate is suddenly lowered, the lighter gas is separated from the mixed liquid, and the gas continues to rise and discharge through the pump discharge port. The degassed liquid returns to the liquid storage chamber, and enters the impeller again by the return hole, and is again mixed with the gas sucked from the suction pipe inside the impeller, and flows to the outer edge of the impeller under the action of the high-speed rotating impeller.
As the process progresses from beginning to end, the air in the suction duct is continuously reduced until the air is exhausted, and the self-priming pump completes the self-priming process, and the centrifugal pump is put into normal operation. Because of the unique venting capability of the centrifugal pump, this self-priming pump can deliver liquid containing gas without the need for a bottom valve and a good sweep function when used on a cruise ship.

Cooling chambers are provided at the bottom of the bearing body of some centrifugal pumps. When the bearing heat rises and the bearing body temperature rises above 70 °C, a cooling liquid pipe joint may be passed through the cooling chamber, such as a coolant circulating cooling such as an IH chemical pump. The sealing mechanism inside the centrifugal pump for preventing liquid from leaking from the high pressure zone to the low pressure zone is a front and rear seal ring, the front seal ring is mounted on the pump body, and the rear seal ring is mounted on the bearing body. When the pump is worn to a certain extent by the long-term operation of the seal ring, And when it affects the efficiency and self-priming performance of the pump, it should be replaced.
The centrifugal pump is generally driven by an electric motor, and the pump body and the suction line are filled with liquid before starting the pump. When the impeller rotates at a high speed, the impeller drives the liquid between the blades to rotate together. Due to the centrifugal force, the liquid is swept from the center of the impeller to the outer edge of the impeller (the flow rate can be increased to 15 to 25 m/s), and the kinetic energy is also increased. When the liquid enters the pump casing, the flow velocity in the volute casing gradually expands, the liquid flow rate gradually decreases, and a part of the kinetic energy is converted into static pressure energy, so that the liquid flows out along the discharge port with a higher pressure. At the same time, a certain vacuum is formed at the center of the impeller due to the liquid being pumped out, and the pressure Pa at the liquid level is higher than the center of the impeller. Therefore, the liquid in the suction line enters the pump under the pressure difference. The impeller rotates continuously, and the liquid is continuously sucked in and out. Because the centrifugal pump can transport liquid, mainly by the action of centrifugal force, it is called centrifugal pump.