What is a mixed flow pump? What are some related failures? How to deal with them?

　　A mixed flow pump is a "pull-out" type pump. When checking and disassembling the impeller and shaft seal, it is not necessary to disassemble the pipes connected to the pump body. It is equipped with a finished pump shaft and oil-lubricated bearings, and the packing gland cover is equipped with a protective sleeve. The oil level of the bearing box can be controlled by a constant oil cup.

　　Mixed flow pumps are suitable for water supply and drainage in factories, mines, cities, and farmland irrigation. Submersible pumps mainly consist of three parts: motor, water pump, and water lifting pipe. The motor is connected to the water pump and works completely submerged in water. The suction port is located at the bottom of the pump, and the discharge port is horizontally arranged. The vertical submersible motor is directly connected to the pump body, and the overload protection device and submersion protection device ensure the safety of operation.

When the prime mover drives the impeller to rotate, it exerts both centrifugal force and axial thrust on the liquid, which is a combination of a centrifugal pump and an axial flow pump, and the liquid flows out obliquely from the impeller. Therefore, it is a pump between a centrifugal pump and an axial flow pump. The specific speed of a mixed flow pump is higher than that of a centrifugal pump and lower than that of an axial flow pump, generally between 300 and 500. Its head is higher than that of an axial flow pump, but its flow rate is smaller than that of an axial flow pump and larger than that of a centrifugal pump.

　　Why do mixed flow pumps fail? How to deal with it?

　　When the rotation direction of the mixed flow pump is incorrect, the current and power of the motor will increase. When the centrifugal pump reverses, the head generated is only 50~60%, and the flow rate also decreases. If the water level difference between the outlet pool and the inlet pool is very large, the water pump will not pump water. If it is small, the pump's water output will be very small. I have encountered this situation many times on site. If the direction mark on the pump is unclear or there is no direction mark. When it is found that the direction of the pump is incorrect, the motor can be eliminated by changing any two phases of the motor.

　　The air intake at the packing gland of the double-suction centrifugal pump breaks the vacuum at the pump suction port, so it cannot suck water. The water pump stops pumping water as soon as it starts, and it is the same after repeated starts to grab water. However, the packing gland cover is already very tight, so the packing has to be replaced again, so this fault is eliminated. Therefore, first tighten the packing gland cover nut, and if the cover is full, the worn and aged packing should be replaced. Sometimes, air may be sucked in from the gap between the two end bushings. At this time, a rubber gasket can be added between the bushing and the impeller to prevent air intake.

The suction of the mixed flow pump exceeds the allowable value, causing cavitation in the pump, and a large number of bubbles block the impeller blade channels, resulting in no water in the pump. The solution is to lower the installation height of the pump, or reduce the water output of the pump, such as closing the outlet gate valve, or trying to raise the water level of the inlet pool.

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