When working on repairing rotary lobe pumps, too many beginners eagerly disassemble a pump, only to put it back together with worse leakage and louder noise. It's not that their hands are clumsy, but that they haven't grasped the know-how. Here are ten common traps, please be careful to avoid them.

1. Disassembling the pump directly without diagnosis  

When a pump fails to deliver flow or trips, many people's first reaction is to disassemble it. In fact, over 80% of faults do not require touching internal parts. First, check whether the power supply has electricity, and measure whether the three phases are missing a phase; then check whether the pump's rotation direction is correct; confirm whether the outlet valve is open and whether the inlet pipeline is leaking air. These steps don't take much time but can save more than half the disassembly and assembly time.

2. Not checking the rotation direction after connecting the wiring incorrectly  

If the three-phase wires are connected backwards, the impeller will rotate in reverse, and the pump will not only fail to deliver water, but the flow will be nearly zero. Beginners often stare blankly at the pressure gauge, never thinking about the rotation direction. For both centrifugal pumps and rotary lobe pumps, before starting, jog the motor and look through the fan cover to see if the rotation direction matches the arrow on the nameplate. If it is reversed, swap any two of the live wires.

- Bonve Pump Industry Cam-Type Twin-Screw Rotary Lobe Pump -

3. Starting the pump without priming – the mechanical seal will quickly be ruined  

If the pump cavity has no water, idling will cause the impeller to generate high temperatures, instantly burning the rubber parts and sealing faces. Correct method: Fill water from the priming port, open the vent valve to release all air until a continuous stream of water comes out, then close the switch. This is called "priming" and can effectively reduce damage to the mechanical seal.

4. Adding too much grease to the bearings  

Many people think that packing grease fully is the right way, but after half an hour of operation the bearing becomes too hot to touch. This is because excessive grease causes churning and heat generation, which actually burns the bearing. A simple formula: Fill amount = (1/2 ~ 2/3) × bearing cavity volume. For low-speed pumps, you can lean toward more; for high-speed pumps, less is better than more.

5. Replacing only the friction pair of the mechanical seal while reusing the old O-ring  

When the mechanical seal leaks, people usually only replace the ceramic and graphite friction faces, thinking the O-ring can still be used. But after reassembly, it still leaks. Upon disassembly, it turns out the aged and hardened O-ring was not compressed properly. When replacing a mechanical seal, you must replace the O-ring, gasket, and spring all together – this guarantees no leakage.

6. Not aligning the coupling concentricity  

The motor and pump are connected with a coupling, and the bolts are tightened, then considered done. After startup, the pump vibrates heavily, the bearings fail within two months, and the mechanical seal leaks frequently – the root cause is the coupling being out of concentricity. Use a dial indicator or even a feeler gauge and a straightedge to control the radial and axial deviation within 0.1mm before tightening.

7. Using a concentric reducer on the inlet pipeline  

When the inlet pipe diameter is larger than the pump inlet, a reducer fitting is needed. Beginners casually install a concentric reducer, which results in air accumulating at the top of the pipe, and the pump easily cavitates when drawing. Correct method: On a horizontal pipe, an eccentric reducer must be used, with the flat side facing up (flat on top), so that air can be carried away by the water flow.

- Bonve Pump Industry Cam-Type Twin-Screw Rotary Lobe Pump -

8. Never repeatedly press the restart button after a trip  

When the pump trips immediately upon starting, many people will continuously hard-start it three or four times. Each start current is 5-7 times the rated current, which rapidly ages the winding insulation and finally burns it out. After a trip, first disconnect the power, measure insulation with a megohmmeter, measure winding resistance with a multimeter, find the cause of overload or short circuit, then try again.

9. When checking for leaks, also pay attention to the inlet pipeline  

If the pump vibrates, the flow is unstable, the pressure fluctuates up and down, and you have checked the mechanical seal, impeller, and bearings thoroughly without finding any problem. Then a slight air leak at the inlet hose or flange joint will cause the pump to suck in air, drastically reducing performance. Apply soapy water to every inlet joint, thread, and gasket; if you see bubbles, that is the leak point.

10. Don't just know what to replace – you need to know why it failed  

If the mechanical seal is replaced three times in a month, or the bearing is replaced five times in a year, don't just complain about poor part quality. The real problems are root causes like vibration, cavitation, contaminants, or misalignment that haven't been resolved. Before each part replacement, you need to think deeply: did it fail due to normal wear, or was it "killed" by something else? Find the root cause, then you can cure it permanently.

Bonve pump always adheres to the philosophy of "Wholeheartedly Making Good Rotor Pumps," committed to providing global customers with customized conveying and mixing solutions. If you have technical inquiries, selection needs, case references, or other cooperation intentions related to Bonve rotor pumps, please feel free to contact us.  

Service Hotline: 0574-87588986 13586591794  

Official Website: www.bvpumps.com  

Business Email: market@bonvepumps.com  

We look forward to working with you to drive efficiency and innovation in industrial fluid transmission with precision technology.