Relationship between pump head and intake and outlet water

High lift pump for low lift pumping

Many machine operators think that the lower the pumping head is, the smaller the load of the motor is. Under the misguidance of such misunderstandings, when choosing a pump, the lift of the pump will often be very high. In fact, for centrifugal pumps, when the pump type 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 head, so the higher the head, the smaller the flow rate, the smaller the power consumption. Conversely, the lower the lift, the greater the flow, and the greater the power consumed. Therefore, in order to prevent motor overload, it is generally required that the actual pumping head of the pump should not be less than 60% of the demarcated head. Therefore, when the high head is used for the low head pumping, the motor is easy to overload and heat, serious burning motor. If it is used in emergency, a gate valve (or a small outlet plugged with wood etc.) must be installed on the outlet pipe to reduce the flow and prevent the motor from overloading. Pay attention to the temperature rise of the motor. If the motor is overheated, turn off the outlet or shut down. This is also prone to misunderstanding, some operators believe that plugging the outlet, mandatory reduction of flow, will increase motor load. In fact, on the contrary, the outlet pipe of the normal high-power centrifugal pump drainage and irrigation unit is equipped with a gate valve. In order to reduce the motor load when the unit starts, the gate valve should be closed first, and then gradually opened after the motor starts.

Large diameter pump with small water pipe pumping

Many users think that this can improve the actual head, in fact, the actual head of the pump = total head - loss head. When the pump type is determined, the total head is a certain; the loss of head mainly comes from pipeline resistance, the smaller the diameter of the pipe is, the greater the resistance is, so the loss of head is greater, so reducing the diameter of the pipe, the actual head of the pump can not increase, but will reduce, resulting in a decline in pump efficiency. Similarly, when small diameter pumps are pumped with large water pipes, the actual head of the pump will not be reduced, but the loss head will be reduced because of the reduction of pipe resistance, and the actual head will be increased. Some users believe that when small diameter pumps are pumped with large water pipes, the motor load will be greatly increased. They believe that when the pipe diameter is increased, the pressure of water in the outlet pipe on the impeller of the pump will be greater, so the motor load will be greatly increased. However, the size of the liquid pressure is only related to the height of the head, but has nothing to do with the size of the water pipe cross-sectional area. As long as the head is fixed, the impeller size of the pump remains unchanged, no matter how large the diameter of the pipe, the pressure acting on the impeller is certain. Only when the pipe diameter increases, the flow resistance decreases, the flow rate increases, and the power consumption increases appropriately. However, as long as the rated head range, no matter how the pipe diameter increases the pump can work normally, and can also reduce pipeline loss, improve pump efficiency.

When installing the intake pipe, the horizontal section is raised horizontally or upward.

In this way, air will be gathered in the intake pipe, reducing the vacuum of the water pipe and pump, reducing the pump head and water output. The correct way is: the horizontal section should tilt slightly toward the water source direction, should not be horizontal, let alone upward tilt.

There are too many elbow on the inlet line.

If more elbow is used on the inlet pipe, the local flow resistance will be increased. And the elbow should be turned in a vertical direction, and it is not allowed to turn in the horizontal direction so as not to gather air.

The pump inlet is directly connected to the elbow.

This will cause uneven distribution of water flowing through the elbow into the impeller. When the diameter of the inlet pipe is larger than that of the pump inlet, an eccentric diameter pipe should be installed. The eccentric part of the variable diameter pipe should be installed on the top and the inclined part should be placed below. Otherwise, the air will be gathered, the water volume will be reduced or the water will not be pumped up, and there will be impact noise. If the diameter of the intake pipe is equal to that of the intake of the pump, a straight pipe should be added between the intake of the pump and the elbow, and the length of the straight pipe should not be less than 2-3 times the diameter of the water pipe.

The inlet pipe with bottom valve is not vertical at the bottom.

If this is installed, the valve can not be closed by itself, causing water leakage. The correct installation method is: the inlet pipe with bottom valve is recommended vertically in the next section. If the terrain condition is not allowed to be installed vertically, the angle between the water pipe axis and the horizontal surface should be above 60 degrees.

The inlet of the inlet pipe is not in the right place.

(1) the distance between the inlet of the inlet pipe and the water tank is less than that of the inlet. If there is sediment and other dirt at the bottom of the pool, when the distance between the inlet and the bottom of the pool is less than 1.5 times of the diameter, the inlet will be blocked because the inlet is not smooth or the sediment is sucked into the pool.

(2) When the inlet depth of the intake pipe is not enough, this will cause the water surface around the intake pipe to produce whirlpools, affecting the water, reducing the amount of water out. The correct installation method is: small and medium-sized pumps should not be less than 300-600 mm in depth, large pumps should not be less than 600-1000 mm.

The outlet pipe is above the normal water level of the outlet tank.

If the outlet is above the normal water level of the outlet tank, although the pump head is increased, the flow rate is reduced. If the water outlet must be higher than the water level of the outlet pool due to terrain conditions, elbows and short pipes should be installed at the outlet to make the pipe siphon and reduce the height of the outlet.