Why do some centrifugal pumps need to be grouted before driving, but some do not?
Centrifugal pumps are self-priming and non-self-priming. The self-priming pump needs to be primed when driving for the first time, and it will not be used in the future! Ordinary centrifugal pumps generally do not need to be pumped if the conveying medium is reversed. Just open the water pump bleed valve before driving to let the medium enter the water pump body. Of course, there is another possibility that the design is unreasonable. In the work station where self-priming pumps should be used, ordinary centrifugal pumps are used, and the pump must be primed every time before driving.
After analyzing the above-mentioned situations, why do we need to irrigate the pump? Starting from the working principle of the centrifugal pump, it is not difficult to analyze the reason. The working principle of the centrifugal pump is that the centrifugal force generated by the high-speed rotation of the impeller blades transports the conveying medium to the outlet of the high-pressure end, then a vacuum is formed at the suction port, and the medium is sucked in again. , And so on. If it is not filled with water (it should be exactly the medium), the centrifugal pump will run without medium and cannot work. Because the gap between the impeller and the pump body is very small, friction and adhesion will occur after dry rotation, which is very prone to mechanical accidents. Lead to the destruction of the pump equipment.
Therefore, in the manual of the centrifugal pump, it will first be stated: No liquid idling is strictly prohibited. The simple point is: the priming of the pump is to remove the air in the impeller of the centrifugal pump, so that the centrifugal pump can work. Holding the pump for a long time will easily cause the temperature of the conveying medium to rise, causing the medium to easily vaporize, resulting in cavitation and other phenomena, which means that this will destroy the pump! When the outlet valve is closed, the pressure of the pumped water increases, and the outlet cannot go out. You should immediately look at the pressure gauge, open the outlet valve, and adjust the centrifugal pump to work under rated conditions.
Centrifugal pumps are impeller pumps, and impeller pumps have no self-priming ability. Filling the pump with water at startup is usually called diversion. The impeller drives the movement of water to perform work, and the suction pipe generates negative pressure before the water can be sucked in. Centrifugal pumps that do not need water are usually equipped with self-priming devices. For example, a water ring pump is installed at the outlet, which will drain the air in the pump before starting. Or if the pipeline layout is reasonable, irrigation and water diversion is not necessary.
