8 mistakes easily made in the use of centrifugal pumps

Posted by angroup on October 7, 2021
Monoblock Pump

Excellent engineering design, proper pump selection, and proper application of pumping technology cannot overcome the hazards that improper use may bring to the pump system, here are 8 easy to make mistakes in the use of centrifugal pumps.

Monoblock Pump

01 High head pumps for low head working conditions

Many people believe that the lower the pump head, the smaller the motor load. Under the misconception of this misconception, when purchasing a pump, the head of the pump is often chosen to be very high.
In fact, for centrifugal pumps, when the pump model is determined, the size of its power consumption is proportional to the actual flow of the pump. The flow of the pump will decrease with the increase of head, so the higher the head, the smaller the flow, the smaller the power consumption. Conversely, the lower the head, the greater the flow, the greater the power consumption. Therefore, in order to prevent motor overload, the actual head of the pump is usually required to be no less than 60% of the rated head. So when the high head pump is used for low head pumping, the motor is easy to overload and get hot, and the motor will be burned up seriously.
If emergency use, it is necessary to install a gate valve on the outlet pipe for regulating the water output to reduce the flow rate and prevent the motor from overload, pay attention to the motor temperature rise, and if the motor is found to be overheated, the outlet flow rate should be shut down or the pump should be stopped in time.

02 Large diameter water pump with small hose to pump water

Many people think that a large diameter pump with a small diameter water pipe can increase the actual head, in fact, the actual head of the pump = total head - loss of head. When the pump model is determined, the total head is certain; the lost head mainly comes from the pipe resistance, the smaller the pipe diameter, obviously the greater the resistance, and therefore the greater the lost head, so after reducing the pipe diameter, the actual head of the pump will not be increased, but will be reduced, resulting in a decline in pump efficiency. Similarly, when a small diameter water pump uses a large diameter water pipe to pump water, it will not reduce the actual head of the pump but will reduce the loss of head due to the reduced resistance of the pipeline, so that the actual head is increased. Some people think that when the small diameter water pump uses the big water pipe to pump water, it will certainly increase the motor load greatly, they think that after the diameter of the pipe increases, the pressure of the water in the outlet pipe to the impeller of the pump is big, so it will increase the motor load greatly. In fact, the size of the liquid pressure is only related to the height of the head and has nothing to do with the size of the cross-sectional area of the water pipe. As long as the head is certain, the impeller size of the pump is unchanged, no matter how big the pipe diameter is, the pressure acting on the impeller is certain. Only after the diameter of the pipe increases, the resistance of water flow will be reduced, and the flow rate will be increased, and the power consumption will be increased appropriately. But as long as in the rated head range, no matter how to increase the diameter of the pump is normal to work, and can also reduce the pipeline loss, improve the efficiency of the pump.

03 When installing the inlet pipe, the horizontal section is horizontal or upward

When installing the water inlet pipe, the horizontal section will gather air in the water inlet pipe and reduce the vacuum of the water pipe and pump, which will lower the suction head of the pump and reduce the water output. The correct practice is: the horizontal section should be slightly inclined to the direction of the water source

04 More elbows used on the centrifugal pump inlet pipe

If more elbows are used in the inlet pipe, it will increase the local water flow resistance. And the elbow should turn in the vertical direction, not allowed to turn in the horizontal direction, so as not to gather air

05 Centrifugal pump inlet directly connected to the elbow

Centrifugal pump inlet and elbow directly connected will make the water flow through the elbow into the impeller when the distribution is uneven. When the diameter of the inlet pipe is larger than the water inlet of the pump, an eccentric reducer should be installed. The flat part of the eccentric reducer should be installed on the top and the beveled part should be installed on the bottom. Otherwise, the air will be gathered, the water output will be reduced or the water will not be pumped, and there will be a crashing sound, etc. If the inlet pipe is equal to the diameter of the water pump inlet, a pipe should be added between the water pump inlet and the elbow, and the length of the straight pipe should not be less than 2~3 times the diameter of the water pipe.

06 The lowermost section of the inlet pipe with the bottom valve is not vertical

If the bottom valve is equipped with the next section of the inlet pipe is not vertical, it will make the valve can not be closed by itself, resulting in water leakage. The correct installation method is the inlet pipe with bottom valve, the next section is best vertical, such as due to terrain conditions can not be installed vertically, the axis of the water pipe and the horizontal plane angle should be more than 60 °.

07 The inlet of the water pipe is not in the right position

The inlet of the water pipe from the inlet pool bottom and pool wall distance is less than the inlet diameter. If there is mud and sand and other dirt at the bottom of the pool, the distance between the inlet and the bottom of the pool is less than 1.5 times the diameter of the inlet, which will cause poor water intake when pumping or suck in mud and sand debris, blocking the inlet.

When the water inlet of the water pipe is not deep enough, this will cause the water surface around the inlet pipe to produce a whirlpool, affecting the water inlet and reducing the water output. The correct installation method is: the water inlet depth of small and medium-sized water pumps shall not be less than 300~600mm, and large water pumps shall not be less than 600~1000mm

08 The outlet pipe mouth is above the normal water level of the outlet pool

If the outlet is above the normal water level of the pool, although the pump head is increased, but the flow rate is reduced. If the water outlet must be higher than the water level of the outlet pool due to the topographic conditions, the elbow and short pipe should be installed at the mouth of the pipe to make the water pipe become siphon type and reduce the height of the outlet.

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