Common Faults of Gear Pump

Figure 1: Gear pump.

1. The Pump Cannot Discharge

Cause: A. the rotation direction is opposite; B. the suction or discharge valve is closed;
C. there is no material at the inlet or the pressure is too low; D. the viscosity is too high, and the pump cannot bite the material.

Solution: A. confirm the rotation direction; B. confirm whether the valve is closed;
C.check valves and pressure gauges; D. check the viscosity of the liquid, and check whether the flow proportional to the speed occurs when running at low speed. Insufficient flow

2. Insufficient Pump Flow

Cause: A. the suction or discharge valve is closed; B. low inlet pressure; C. the outlet pipeline is blocked; D. stuffing box leakage; E. low speed.

Solution: A. confirm whether the valve is closed; B. check whether the valve is open; C.confirm whether the discharge is normal; D. fastening; When a large amount of leakage affects production, stop operation and disassemble it for inspection; E. check the actual speed of the pump shaft.

Figure 2: Disassemble it for inspection.

3. Abnormal Sound

Cause: A. large eccentric coupling or poor lubrication B. motor failure; C. abnormal reducer; D. poor installation of shaft seal; E. shaft deformation or wear.

Solution: A. align or fill lubricating grease; B. check the motor; C. check the bearings and gears; D. check the shaft seal; E. shutdown disassembly inspection.

4. Excessive Current

Cause: A. the outlet pressure is too high; B. melt viscosity is too high; C. poor assembly of shaft seal; D. shaft or bearing wear; E. motor failure.

Solution: A. check downstream equipment and pipelines; B. check viscosity; C. check the shaft seal and adjust it properly; D. check whether the turning gear is too heavy by hand after parking; E. check the motor.

Figure 3: Check the shaft seal.

5. The Pump Stops Suddenly

Cause: A. power failure; B. motor overload protection; C. the coupling is damaged; D. the outlet pressure is too high; E. abnormal biting in the pump; F. the shaft and bearing are stuck.

Solution: A. check the power supply; B. check the motor; C. open the safety cover and crank for inspection; D. check the instrument interlocking system; E. after parking, confirm the positive and negative turntable cars; F. turning confirmation.

6. Oil Leakage

Cause: A. the shaft seal is not adjusted properly; B. the seal ring is worn and the clearance is large; C. the friction surfaces of the dynamic and static rings of the mechanical seal are damaged with time; D. spring relaxation.

Solution: A. readjust; B. tighten the gland bolts appropriately or replace the sealing ring; C. replace the dynamic and static rings or regrind; D. replace the spring.

7. Other Faults

Figure 4: High quality gear pump.

7.1 Cause

① The tooth side clearance of the rotors is too large, which makes the suction oil chambers interconnected. The volumetric efficiency is significantly reduced, and the output flow is not enough;
② Axial clearance is too large;
③ The joint surface in the oil suction pipeline is not sealed tightly, so that the pump sucks in air and the effective suction flow is reduced;
④ Poor oil absorption. For example, the suction flow is reduced due to the excessive viscosity of the oil and the blockage of the oil filter by dirt;
⑤ The overflow valve is stuck at the half opening position, and part of the flow from the pump returns to the oil tank through the overflow valve, which makes the flow into the system insufficient. At this time, there is a fault that the system pressure does not go up.

7.2 Exclusion Method

① Replace the inner and outer rotors to make the backlash within the specified range (generally less than 0.07mm);
② Grind the two end faces of the pump body to ensure that the axial clearance of the inner and outer rotors is within 0.02~0.05mm after assembly;
③ Replace the damaged oil suction pipe seal, wrap the threaded part of the pipe joint with Teflon tape, and then tighten the pipe joint;
④ Select the oil with proper viscosity, and clean the oil inlet filter to ensure smooth oil absorption. And increase the oil suction pipe diameter according to the situation;
⑤ Repair the overflow valve and eliminate the phenomenon that the overflow valve reduces the effective flow of the pump.

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