Why Can't Centrifugal Pumps Pump Water

Apr 04, 2025

Centrifugal pumps have a simple structure, are easy to use and maintain, and have high efficiency. Centrifugal pumps are the most widely used type of water pump in agriculture, but even the best things have some problems. Centrifugal pumps sometimes cannot lift water. Here are some analyses of our company's response to this problem:

1. There is air in the inlet pipe and pump body

(1) Some people do not fill enough water before starting the water pump, and sometimes it appears that the filled water has overflowed from the vent hole, but the pump shaft has not been rotated to completely discharge the air, resulting in some air remaining in the inlet pipe or pump body.

(2) The reverse flow direction of the inlet pipe should have a slope greater than 0.5%. If it tilts upwards, air will remain in the inlet pipe, reducing the vacuum degree in the water pipe and pump, and affecting water absorption.

(3) Due to long-term wear and tear or excessive pressure on the packing of a centrifugal pump, a large amount of water overflows from the gap between the packing and the pump shaft sleeve, causing external air to enter the interior of the pump through the gap and affecting water lifting.

(4) The inlet pipe is prone to corrosion and holes on the pipe wall due to being placed in water. After the water pump works, the water surface continuously drops. When these holes are exposed to the water surface, air enters the inlet pipe through the holes.

(5) Cracks at the bend of the inlet pipe and small gaps at the connection between the inlet pipe and the water pump may allow air to enter the inlet pipe.

2. The speed of the water pump is too low

(1) Human factors. Some people, due to motor damage, randomly install another motor to drive it, resulting in low flow rate, low head, or even no water supply.

(2) The drive belt is worn. Many large centrifugal pumps use belt transmission, but due to long-term use, the transmission belt may become loose and slip, thereby reducing the speed of the water pump.

(3) Improper installation. The center distance between the two pulleys is too small or the two shafts are not very parallel, the transmission belt is too tight when installed on top, resulting in a small wrap angle, calculation errors in the diameter of the two pulleys, and a large eccentricity between the two shafts of the water pump in the coupled transmission, all of which can cause changes in the speed of the water pump.

(4) Mechanical failure of the water pump itself. Loosening of the fastening nut between the impeller and the pump shaft or deformation and bending of the pump shaft can cause excessive movement of the impeller, direct friction with the pump body, or damage to the bearings, all of which may reduce the speed of the water pump.

(5) The maintenance of the power machine is not working properly. The motor loses magnetism due to burnt windings, and changes in winding turns, wire diameter, and wiring methods during maintenance, or incomplete troubleshooting during maintenance, can also cause changes in the speed of the water pump.

3. The suction distance is too large

Some water sources are deep, and the surrounding terrain of some water sources is relatively flat, ignoring the allowable suction range of the water pump, resulting in less or no water absorption. Centrifugal pumps have their maximum allowable suction range, generally between 3-8.5 meters. When installing a water pump, it is important not to only consider convenience and simplicity.