DAITO KOGYO CO., LTD.
TOP What is gear pump? Quotation request Installation examples Troubleshooting Q&A Company profile
TOPTroubleshooting
  Troubleshooting
Gear pumps problems are divided into two main categories:
those resulting from the pump itself,
and others from issues other than the pump.

 
■The top nine problems of gear pumps are:
1. Inability to rotate 6. Heating of pump
2. Leakage 7. Swing of pressure indicator
3. Insufficient capacity 8. Overload of motor
4. Insufficient discharge pressure 9. Abnormal noise/vibration
5. Inability to suction  
  These problems are explained below.

Details of problems

1. Inability to rotate
When galling occurs due to a foreign object in the piping
When galling occurs because the temperature of the pumped liquid rises and the side clearance disappears
When idled or grazing operation is performed for a long time
When galling occurs because the temperature of the liquid rises due to extended operation with the built-in safety valve working, and the side clearance disappears
When galling occurs because the side clearance disappears due to distortion of cast products
When a problem such as shaft breakage occurs
When galling occurs because the gears come in contact with the side plate due to misalignment of the pump or too much tension of the V belt
When galling occurs due to operation with the discharge pipeline closed, or operation exceeding the specified pressure
When galling occurs due to wear of the parts inside the pump, and especially when wear of the shaft bearing (metal)/bearing has progressed
Due to failure of the power engine or motor, etc.
Due to defect of electric wiring, switch, etc.
* When scratching occurs due to such causes as idling, in some cases the inability to rotate does not occur immediately after the accident, but after a while the scratching will lead to the inability to rotate. Scratching leading to this trouble is often caused during commissioning immediately after installation of the pump.
▲ to top of page   



2. Leakage
(1) Leakage from seal
  When the pumped liquid and packing/seal material do not match
  When there is pushing pressure on the suction side
  When negative rotation occurs
  When the shaft is worn out
  When the viscosity of pumped liquid becomes lower than the specified viscosity
  When the seal surface is flawed
  When foreign objects such as slurry have entered the sealing liquid or pumped liquid of the mechanical seal
  When the seal surface of the mechanical seal is worn out
  Due to defective assembly, or uneven contact of the seal surface
  When the pumped liquid hardens due to sliding heat of the mechanical seal
  When the sealing liquid of the mechanical seal undergoes thermal expansion
  When pressure is placed while the pump is stopping, causing deformation/damage of the mechanical seal parts
  * Structurally, it is impossible to completely stop liquid leakage of gland packings, oil seals, or mechanical seals. If you need to completely prevent liquid leakage, please use a seal-less gear pump.

(2) Leakage from other places
  Defective assembly such as foreign objects in juncture of the case and cover
  When abnormally high pressure is applied compared with the specified conditions
  When electromagnetic valves are suddenly closed or pressure does not escape due to narrow bypass piping
  Damage to the gaskets, defective or uneven application of packing agent
▲ to top of page   



3. Insufficient capacity
When the safety valve is working (the pressure indicator swings)
When there are foreign objects on the seat surface of the safety valve
When there is air leakage from the suction pipeline, or pump seal section
When excessive resistance (cavitation) occurs on the suction side
  When the viscosity of the pumped liquid becomes high
  When the valve on the suction side is turned down too much
  When the head of fluid on the suction side lessens
  When the strainer is clogged
  When the piping is small for the viscosity/flow rate of the pumped liquid
  When the rotation speed is excessive for the viscosity of the pumped liquid
When the specified pressure is exceeded
When the viscosity of the pumped liquid becomes significantly lower than the specification
When regular rotation speed is not obtained due to slipping, etc. of the belt
When the clearance in the pump becomes large due to wear
When the flowmeter is malfunctioning
▲ to top of page   



4. Insufficient discharge pressure
When the capacity is insufficient
When the safety valve is working (the pressure indicator swings)
When there are foreign objects on the seat surface of the safety valve
When excessive resistance (cavitation) occurs on the suction side
  When the viscosity of the pumped liquid becomes high
  When the valve on the suction side is turned down too much
  When the head of fluid on the suction side lessens
  When the strainer is clogged
  When the piping is small for the viscosity/flow rate of the pumped liquid
  When the rotation speed is excessive for the viscosity of the pumped liquid
When the resistance of the discharge pipeline becomes excessively small
  When the resistance of the nozzle due to wear of the nozzle.
  When the resistance of the discharge pipeline becomes lower due to decrease of the viscosity of the pumped liquid.
When the clearance in the pump becomes large due to wear
When the pressure indicator is malfunctioning
▲ to top of page   



5. Inability to suction (Although the pump rotates, liquid is not drawn)
When the safety valve is working (the pressure indicator swings)
When there are foreign objects on the seat surface of the safety valve
When excessive resistance (cavitation) occurs on the suction side
  When the viscosity of the pumped liquid becomes high
  When the valve on the suction side is turned down too much
  When the head of fluid on the suction side lessens
  When the strainer is clogged
  When the piping is small for the viscosity/flow rate of the pumped liquid
  When the rotation speed is excessive for the viscosity of the pumped liquid
When there is air leakage on the suction side
When the suction pipe is not dipped (immersed) in the liquid (e.g. the tank is empty)
During suction from an underground tank, for example, if the viscosity of the pumped liquid is low and there are no check valves (non-return valves) in the suction piping, or even if there are check valves, they do not function properly, and all the liquid falls down when the pump stops.
When the inside of the pump is dry, and the required pressure cannot be generated on the suction side
When the flow rate of the suction pipe is excessively small
▲ to top of page   



6. Heating of pump
When the temperature of the liquid itself is abnormally high because the tank capacity is excessively small in a closed circuit
When the built-in safety valve of the pump is frequently activated, or remains activated
When the gland packing is closed too tightly
When the shaft bearing, shaft seal, etc. of the pump generate heat due to wear of parts, for example
When there is misalignment or the V belt is too tight
  Due to warp, etc. of the base
  When installation of the pump is poor
▲ to top of page   



7. Swing of pressure indicator
When the safety valve is working (chattering, etc.)
When air is sucked in from the suction piping
When the pumped liquid is partially vaporizing in the suction piping (vapor lock)
When excessive resistance (cavitation) occurs on the suction side
When there is an air pocket in the piping
When the pressure indicator is malfunctioning
* Depending on the cause, in addition to swinging of the gauge, there may also be vibration, noise or decrease of capacity.
Please also check the situation around the pump.
▲ to top of page   



8. Overload of motor
When the discharge pressure is higher than the specification due to operation with the discharge pipeline blocked or closed, etc.
When the rotation speed is higher than the specification
When the viscosity of pumped liquid increases due to a temperature change, for example
When the inside of the pump is worn
When "galling" of the gear or "burning" of the shaft bearing (metal) is about to occur
When foreign objects are caught
When the gland packing is closed too tightly
When the pump is misaligned or the V belt is too tight
  Due to warp, etc. of the base
  When installation of the pump is poor
▲ to top of page   



9. Abnormal noise/vibration  Items of examination
When the safety valve is working (the pressure indicator swings)
When excessive resistance (cavitation) occurs on the suction side
  When the viscosity of the pumped liquid becomes high
  When the valve on the suction side is turned down too much
  When the head of fluid on the suction side lessens
  When the strainer is clogged
  When the piping is small for the viscosity/flow rate of the pumped liquid
  When the rotation speed is excessive for the viscosity of the pumped liquid
When the flow rate is excessive and turbulent flow is occurring in the piping
When there is air suction in the suction pipeline
When the pump is idling
Engagement of the gears is defective, backlash is inappropriate, or containment phenomenon occurs
When the piping before and after the pump is resonating/sympathizing
When the coupling is misaligned
When the inside of the pump is worn
When noise is generated from the motor or geared motor
Wear of coupling or coupling pin, rubber
▲ to top of page   

  Although the overview of problems of gear pumps is itemized above, there are many cases where causes of problems are hard to be identified. Also, when some causes overlap, identifying the causes becomes even more difficult. In order to prevent problems, please read the Instruction manual and operate accordingly.

Instruction manual


  DAITO KOGYO CO., LTD.
Copyrigh(C) 2008 DAITO KOGYO CO.,  LTD. All Rights Reserved.
TOP Japanese Chinese