Why the rotary lobe pump can’t self priming liquid?

Why the rotary lobe pump can’t self priming liquid?

In the process of using the rotary lobe pump, it’s hard to self priming liquid or can’t at sometime, why and what are the causes of the lobe pump can’t self priming? There are four main factors.

1. Air inside the inlet pipe and pump

(1) The horizontal section of the inlet pipe in contact with the lobe pump shall have a downward slope of more than 0.5% in the reverse direction of the water flow, and the end connected to the inlet of the lobe pump shall not be completely horizontal. If upturned, the inlet pipe will retain air, reducing the vacuum in the water pipe and lobe pump, affecting water absorption.

(2) The packing of the rotary lobe pump has been worn or the packing pressure is too loose due to long-term use, resulting in a large amount of water from the gap between the packing and the shaft sleeve of the pump, the result is the external air from these gaps into the inside of the pump, affecting the water.

(3) Due to long-term potential underwater water, holes appear in the pipe wall corrosion, and the water surface keeps dropping after the lobe pump works. When these holes come out of the water surface, air enters the civil water inlet pipe from the holes.

(4) Cracks appear at the elbow of the inlet pipe, and tiny gaps appear at the connection between the inlet pipe and the pump, which may cause air to enter the inlet pipe.

2, The speed of lobe pump is too low

(1) Human factors. Some users, due to the damage of the original motor, randomly equipped with another motor to drive, resulting in a small flow, low head or even do not water consequences.

(2) Mechanical failure of the rotary lobe pumps itself. Impeller and pump shaft nut loose or pump shaft deformation and bending, resulting in more impeller, direct friction with the pump body, or bearing damage, are likely to reduce the pump speed.

(3) Poor maintenance of the engine. Motor because of winding burn, and loss of magnetism, maintenance winding turns, wire diameter, wiring changes, or maintenance failure not completely eliminate factors will also make the pump speed change.

3. The suction range is too large

Some water source is deeper, some water source of the periphery of the terrain is more flat, and ignore the rotary lobe pump allowable suction, resulting in little or no suction water. To know the lobe pump suction can be established at the vacuum is limited, the vacuum suction is about 10 meters high water column, and the lobe pump can not establish the vacuum. And the vacuum degree is too large, easy to make the pump water gasification, on the lobe pump work. So each centrifugal pump has its maximum allowable suction range, generally between 3-8.5 meters. The installation of CAM rotary lobe pump can not only figure convenient and simple.

4, The flow of water inside and outside of the pipe resistance loss is too large

Some users have measured that although the vertical distance from the reservoir or water tower to the source water surface is still slightly less than the rotary lobe pump head, the water volume is still small or can not be lifted. The reason is often the pipe is too long, the pipe bends, and the water flow in the pipe resistance loss is too large. The reason is often the pipe is too long, the pipe bends, and the water flow in the pipe resistance loss is too large. In general, the resistance of 90 degree bend is greater than that of 120 degree bend. The head loss of each 90 degree bend is about 0.5-1 meter, and the head loss is about 1 meter due to the resistance of every 20 meters. In addition, some users’ also optional lobe pump in and out pipe diameter, these also have a certain impact on the head.

Other factors

(1) The bottom valve cannot be opened. It is usually due to the rotary lobe pump to wait too long, the bottom valve gasket is stuck dead; the bottom valve without gasket may rust dead.

(2) The filter net of the bottom valve is blocked; Or the bottom valve potential in the water sludge layer caused by screen blockage.

(3) Serious impeller wear. The wear of impeller blades after long-term use affects the performance of the rotary lobe pump.

(4) Gate valve can check valve failure or blockage will cause flow reduction or even can not pump water.

(5) Leakage of the outlet pipeline will also affect the water withdrawal.