Eight misuses of pipeline centrifugal pumps

First, the pipeline centrifugal pump pipeline matching some of the centrifugal pump users believe that this can increase the actual head, in fact, the actual pump head = total head ~ loss head. When the pump model is determined, the total head is constant; the loss head mainly comes from the pipe resistance, the smaller the pipe diameter is obviously the greater the resistance, so the greater the loss head, so after reducing the pipe diameter, the actual lift of the pump can not only increase Instead, it will decrease, leading to a drop in pump efficiency. Similarly, when a small-diameter pump uses a large pipe to pump water, it will not reduce the actual head of the pump. Instead, it will reduce the loss head due to a reduction in the resistance of the pipe, which will increase the actual lift. It is also considered that the small-diameter pumps will inevitably greatly increase the motor load when they pump water. They believe that after the pipe diameter is increased, the water in the outlet pipe will have a large pressure on the pump impeller, which will greatly increase the motor load. As everyone knows, 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 constant, the impeller size of the water pump is constant. Regardless of the diameter, the pressure acting on the impeller is constant. Only after the pipe diameter increases, the flow resistance will decrease, the flow will increase, and the power consumption will increase appropriately. But as long as the rated head range, regardless of how to increase the diameter of the pump can work properly, but also can reduce the loss of pipelines, improve the pump efficiency.

Second, the high lift pump for pumping low lift pump Some users of centrifugal pumps believe that the lower the pumping head, the smaller the motor load. In the misunderstanding of this misunderstanding, when choosing a water pump, the head of the pump is often selected very high. In fact, for the centrifugal pump, when the pump model is determined, the power consumption is proportional to the actual flow of the pump. The flow of the pump will decrease with the increase of the head, so the higher the lift, the smaller the flow and the smaller the power consumption. Conversely, the lower the head, the greater the flow and the greater the power consumed. Therefore, in order to prevent motor overload, it is generally required that the pump's actual pumping head should not be less than 60% of the nominal head. Therefore, when the high head is used for pumping the pump with too low lift, the motor is easily overloaded and generates heat. In severe cases, the motor can be burned. If it is used in emergency, it must be installed on the outlet pipe to adjust the amount of water out of the gate valve (or a small outlet with a small object such as wood) to reduce the flow and prevent the motor from overloading. Pay attention to the temperature rise of the motor. If the motor is found to be overheated, turn off the flow at the outlet or turn off the power immediately. This is also easy to misunderstand. Some operators think that blocking the outlet and forcing a reduction in traffic will increase the motor load. In fact, on the contrary, regular high-power centrifugal pump irrigation units are equipped with gate valves on the outlet pipe. In order to reduce the motor load when the unit is started, the gate valve should be closed first. This is the reason that the valve is gradually opened after the motor is started.

Third, the pipe elbow in the inlet pipe of the centrifugal pump is much. If there are many elbows used in the inlet pipe, it will increase the local flow resistance. And the elbow should be turned in the vertical direction, not allowed to turn in the horizontal direction, so as not to gather air.

Fourth, when installing the water inlet pipe, the horizontal section may be horizontal or upward. This will cause the air in the inlet pipe to gather air, reduce the degree of vacuum of the water pipe and the water pump, reduce the water absorption of the pump, and reduce the amount of water discharged. The correct approach is: The horizontal section should be slightly inclined to the direction of the water source, should not be horizontal, but not upturned.

Fifth, the inlet of the centrifugal pump is directly connected with the elbow, which causes uneven distribution of the water flow through the elbow into the impeller. When the diameter of the inlet pipe is larger than the inlet of the pump, an eccentric reducer should be installed. Eccentric reducer tube is to be mounted on the flat surface, and the inclined surface is mounted on the bottom. Otherwise, the air will gather, the amount of water will be reduced or the water will not be able to be pumped, and there will be a crash. If the inlet pipe and the water pump inlet diameter are equal, a straight pipe shall be added between the inlet of the pump and the elbow. The length of the straight pipe shall not be less than 2 to 3 times the diameter of the pipe.

Sixth, the pipeline centrifugal pump outlet pipe in the outlet tank above the normal water level If the outlet in the outlet tank above the normal water level, although the increase of the pump head, but reduce the flow. If due to topographical conditions, the water outlet must be higher than the water level of the water tank, then elbows and short tubes shall be installed at the nozzle to make the water pipe a siphon type and reduce the height of the water outlet.

7. The inlet of the inlet pipe is not located at the inlet of the inlet pipe and the distance between the bottom of the inlet pipe and the wall of the pool is less than the diameter of the inlet. If there is sediment and other dirt at the bottom of the tank, when the distance from the water inlet to the bottom of the tank is less than 1.5 times of the diameter, it will cause poor water intake or suction of muddy debris and block the water inlet when pumping.

2 If the depth of water entering the water inlet of the inlet pipe is not enough, this will cause vortexes on the water surface around the inlet pipe, affecting the water intake and reducing the amount of water discharged. The correct installation method is: the water depth of small and medium-sized pumps shall not be less than 300-600mm, and the large-sized water pumps shall not be less than 600-1000mm.

8. When the bottom valve is set, the bottom section of the water inlet pipe is not vertical. If it is installed like this, the valve cannot be closed by itself, causing water leakage. The correct installation method is: The inlet pipe is equipped with a bottom valve, and the bottom section is preferably vertical. If it cannot be installed vertically due to topographic conditions, the angle between the axis of the water pipe and the horizontal plane should be above 60°.

Pipeline centrifugal pump is the most widely used pump in various fields. As long as the majority of users understand the eight errors of the pipeline centrifugal pump, try to avoid the above mentioned.