The installation of the inlet pipe of a self-priming pump is an important part that affects the suction range of the pump. Poor installation, air leakage, long, thick, and small pipes, as well as the number and degree of bends, will directly affect the self-priming pump's ability to suck in incoming water.
1. Large caliber self-priming pump with small water pipe for water supply
Many users believe that this can increase the actual head of the self-priming pump. The actual head of a self-priming centrifugal pump is equal to the total head minus the lost head. After determining the model of the water pump, the total head is fixed; The loss of head is mainly due to pipeline resistance. The smaller the pipe diameter, the greater the resistance, resulting in a greater loss of head. Therefore, reducing the pipe diameter not only fails to increase the actual head of the centrifugal pump, but also decreases, leading to a decrease in the efficiency of the self-priming pump. Similarly, when a small diameter water pump uses a large water pipe to pump water, the actual head of the pump will not decrease. Instead, the loss of head will be reduced due to the decrease in pipeline resistance, resulting in an increase in the actual head.
Some experts believe that when a small diameter water pump uses a large water pipe to pump water, it will definitely greatly increase the motor load. They believe that as the pipe diameter increases, the pressure of the water in the outlet pipe on the pump impeller will increase, thus greatly increasing the motor load. Little did they know that the magnitude of liquid pressure is only related to the head, and not to the cross-sectional area of the water pipe. As long as the head is constant, the impeller size of the self-priming pump remains unchanged, and the pressure acting on the impeller is constant regardless of the diameter of the pipe. However, as the diameter of the pipe increases, the water flow resistance will decrease, resulting in an increase in flow rate and an appropriate increase in power consumption. But as long as it is within the rated head range, the water pump can work normally regardless of how the pipe diameter is increased, and it can also reduce pipeline losses and improve pump efficiency.
2. When installing the inlet pipeline of the self-priming pump, the degree may vary or rise upwards
This will gather air in the inlet pipe, lower the vacuum level of the water pipe and centrifugal pump, reduce the suction head of the centrifugal pump, and decrease the water output. The accurate approach is that the degree range should be slightly inclined towards the direction of the water source, not to a certain degree, let alone upward.
3. There are many elbows used on the inlet pipeline of the self-priming pump
If more elbows are used on the inlet pipeline, it will increase local water flow resistance. And the elbow should turn in the vertical direction, not in the degree direction, to avoid gathering air.
4. The inlet of the self-priming pump is directly connected to the elbow
This will cause uneven distribution of water flow when it enters the impeller through the elbow. When the diameter of the inlet pipe is larger than that of the water pump inlet, an eccentric variable diameter pipe should be installed. The flat part of the eccentric variable diameter pipe should be installed on top, and the inclined part should be installed on the bottom. Otherwise, it will gather air, reduce water output or fail to pump water, and there will be collision sounds.
If the diameter of the inlet pipe is equal to that of the water pump inlet, a straight 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.
5. The next section of the inlet pipe of the self-priming pump equipped with a bottom valve is not vertical
If installed in this way, the valve cannot close on its own, causing water leakage. The accurate installation method is to install the inlet pipe with a bottom valve, and the next section should be vertical. If vertical installation is not possible due to terrain conditions, the angle between the axis of the water pipe and the degree plane should be at least 60 °.
6. The position of the inlet of the self-priming pump's inlet pipe is incorrect
(1) The distance between the inlet of the self-priming pump inlet pipe and the bottom and wall of the inlet pool is less than the diameter of the inlet. If there is sediment and other pollutants at the bottom of the pool, and the distance between the inlet and the bottom of the pool is less than 1.5 times the diameter, it will cause poor water intake or suction of sediment and debris during pumping, blocking the inlet.
(2) When the water inlet depth of the inlet pipe is not sufficient, it will cause vortices on the water surface around the inlet pipe, affecting the water intake and reducing the water output. The accurate installation method is that the inlet depth of small and medium-sized water pumps should not be less than 300-600mm, and the inlet depth of large water pumps should not be less than 600-1000mm
7. The outlet of the sewage pump is above the normal water level of the outlet pool
If the outlet of the sewage pump is above the normal water level of the outlet pool, although it increases the pump head, it reduces the flow rate. If due to terrain conditions, the outlet must be higher than the water level of the outlet pool, then elbows and short pipes should be installed at the pipe mouth to make the water pipe siphon and lower the outlet height.
8. High head self-priming sewage pump operates at low head
Many customers usually believe that the lower the head of a centrifugal pump, the lower the motor load. Under this misconception, when purchasing a water pump, they often choose a high head. In fact, for sewage pumps, when the model of the sewage pump is determined, the power consumption is directly proportional to the actual flow rate of the sewage pump. The flow rate of the sewage pump will decrease with the increase of the head, so the higher the head, the smaller the flow rate, and the lower the power consumption. On the contrary, the lower the head, the greater the flow rate, and the greater the power consumption. Therefore, in order to prevent motor overload, it is generally required that the actual pumping head of the water pump should not be less than 60% of the calibrated head.
So when high head is used for low head pumping, the motor is prone to overload and heat generation, and in severe cases, it can burn out the motor. If emergency use is required, a gate valve must be installed on the outlet pipe to adjust the water flow rate (or a small outlet must be blocked with wood or other materials), in order to reduce the flow rate and prevent motor overload. Pay attention to the temperature rise of the motor. If the motor is found to be overheated, the outlet flow rate should be reduced or the machine should be shut down in a timely manner.
This can also easily lead to misunderstandings. Some operators believe that blocking the water outlet and forcibly reducing the flow rate will increase the motor load. In fact, on the contrary, the outlet pipes of regular high-power centrifugal pump irrigation units are equipped with gate valves. In order to reduce the motor load during unit startup, the gate valves should be closed first, and gradually opened after the motor starts. This is the principle.
