Common misconceptions of pipeline pumps

Misconception one: The actual lift can be increased by reducing the pipe diameter.
Some users of centrifugal pump think that this can improve the actual lift. The truth is that the actual lift of the pump is equal to the total lift minus the loss lift. When the pump model is determined, the total lift is certain. The loss pump lift is mainly from the pipeline resistance And the smaller the diameter, the greater the resistance, so the larger the pump lift is. Therefore, after the pipe diameter is reduced, the actual lift of the pump cannot be increased. On the contrary, it will decrease and lead to a drop in pump efficiency. In the same way, when the small-diameter water pump is pumped with a large water pipe, the actual lift of the water pump will not be lowered, but the loss lift will be reduced due to the decrease of the resistance of the 
pipeline, so that the actual lift is increased.

Some of them also believed that the small-diameter water pump will greatly increase the motor load when pumping water with a large water pipe. They think that the water in the outlet pipe will have a large pressure on the pump impeller after the pipe diameter is increased, thus greatly increasing the motor load. As everyone knows, the pressure of the liquid pressure is only related to the height of the 
lift, and has nothing to do with the cross-sectional area of the water pipe. As long as the lift is certain, the impeller size of the pump is constant, and the pressure acting on the impeller is constant regardless of the diameter of the pipe. Only when the pipe diameter is increased, the water flow resistance will decrease, and the flow rate will increase, and the power consumption will also increase appropriately. However, as long as it is within the rated lift range, the pump can work normally regardless of the pipe diameter, and it can also reduce the pipeline loss and improve pump efficiency.

Misconception two: High lift pump uses in low lift pumping.
Some users believe that the lower the pumping lift, the smaller the motor load. Under this misconception, they often select high lift pumps when purchasing. In fact, for a centrifugal pump, when the pump model is determined, the power consumption is proportional to the actual flow of the pump. The flow rate of the pump will decrease with the increase of the lift, so the higher the lift, the smaller the flow and the power consumption. Conversely, the lower the lift, the greater the flow and the power consumed. Therefore, in order to prevent the motor from overloading, it is generally required that the actual pumping stroke of the pump should not be less than 60% of the nominal head. When the high lift pump is used for low lift pumping, the motor is easily overloaded and heated, and in severe cases, the motor can be burnt. If it is used in an emergency, a gate valve (or a small outlet with wood or the like) for adjusting the amount of water must be installed on the outlet pipe to reduce the flow to prevent motor overload. Pay attention to the temperature rise of the motor. If the motor is overheated, turn off the flow of the small outlet or shut down. Some operators think that blocking the water outlet and forcibly reducing the flow will increase the motor load. In actual conditions, the gate valve of the regular high-power centrifugal pump drainage and irrigation unit is equipped with a gate valve. In order to reduce the motor load when the unit is started, the gate valve should be closed firstly, and then gradually opened after the motor is started.

Misconception three: Use many elbows on the centrifugal pump inlet pipe.
If there are many elbows on the inlet pipe, it will increase the local flow resistance. Besides, the elbow should turn in the vertical direction, and it is not allowed to turn in the horizontal direction to avoid air accumulation.

Misconception four: When installing the water inlet pipe, the horizontal section is horizontal or upturned.
This will cause air to accumulate in the inlet pipe, reducing the vacuum degree of the water pipe and pump, the suction lift of the pump and the amount of water. The correct way is that the horizontal section should be slightly inclined to the water source, and should not be horizontal or lifted upwards.

Misconception five: The inlet of the centrifugal pump is directly connected to the elbow.
This will result in uneven distribution of water as it passes through the elbow into the impeller. When the inlet pipe diameter is larger than the water pump inlet, an eccentric reducer should be installed. The flat part of the eccentric reducer is to be mounted on the upper part, and the inclined part is placed below. Otherwise, the air will be collected, and the amount of water will be reduced or the water will not be pumped, along with knocking noise. If the inlet pipe and the water inlet of the pump are equal in diameter, a straight pipe should be added between the water inlet and the elbow of the pump, and not be less than 2 to 3 times the diameter of the water pipe.

Misconception six: The centrifugal pump outlet pipe is above the normal water level of the outlet.
If the water outlet is above the normal water level of the water outlet, although the pump lift is increased, the flow is reduced. If the water outlet must be higher than the water level of the pool due to terrain conditions, the elbow and short pipe should be installed at the opening of the pipe to make the water pipe siphon type and reduce the height of the water outlet.

Misconception seven: The inlet of the inlet pipe is not in the right position. 
When the water inlet of the inlet pipe is not deep enough, this will cause a vortex on the water surface around the inlet pipe, affecting the inflow and reducing the amount of water. To correct this, the water depth of the small and medium-sized water pump should not be less than 300 mm to 600 mm, and the large water pump should not be less than 600 mm to 1000 mm.

Misconception eight:  When the bottom valve is set, the bottom section of the inlet pipe is not vertical.
If installed in this way, the valve cannot be closed by itself, which will cause water leakage. The bottom section of the inlet pipe with the bottom valve is preferably vertical. If it cannot be installed vertically due to terrain conditions, the angle between the water pipe axis and the horizontal plane should be 60° or more.


Share this post

Related News