Gear Pump Fault Finding Chart

Externally Lubricated Pumps Apx Series, Neoprene Seal Gear Pump, Gear Pump Supplier, Mumbai, India
Sr. No Fault Cause Action
I. a) Pump does not prime 1.Rotation wrong connection on motor. Check rotation .If necessary changes
    2. Pump is dry Fill pump initially with oil
    3. Suction line is not tight Tighten all bolts and nuts on suction side. If necessary, pressure test suction line. Attach vacuum gauge which should show approximately 20 inc. Hg Vacuum at closed suction valve.
    Relief Valve not tight. Damaged valve joint Foreign body between valve seat and valve Remove valve and check seal. If necessary grind in. Check joint between suction and discharge opening in the pump. if necessary replace joint. Remove foreign body. Incase of damage to valve seat, grind in Tighten bolts of cover
I. b) In the case of working against closed discharged line 1.Evacuated air cannot pass through the pressurized oil column and streams back into the suction line Arrange deaeration cock on discharge side of pump. When pump is started, open this cock until all air is exhausted and then close. In the suction line, when switching off pump, remains full.
II. Loss of output 1.Speed too slow Check speed by means of a tacho meter. Check frequency and voltage motor name plate. Check pump as in the case of overload, speed can be dropped. Check star-delta and compare with voltage
    2.Relief valve opens too soon Remove valve cover and adjusting screw. if spring is fatigued, replace. Take care when adjusting that the pressure rise with closed discharged valve does not overload, speed can be dropped. Check star-delta and compare with voltage.
    3.Loss in output due to air in stuffing box See fault 1,paragraph 3
    4.Suction line friction too great Fit vacuum gauge and check suction lift which should not be more than 5-6 MLC.
    A) Suction pipe too small In the case of items (a), (b), & (d) only, a large suction line or a reduction in length can help.
    B) Suction line too long In case of (C) clean the filter  element.
    C) Suction filter blocked  
    D) Viscosity too high.  
III Pump is noisy 1.Badly aligned coupling Disconnect pump for motor and align coupling
  A) Mechanical Noise 2. Spindle not running Strip motor and remove main spindle (as operation that should be carried out only by an expert.) Test with clock gauge between centers.
    3.Gear flanks are damaged Remove gears and correct damaged flanks by foreign bodies with oil stone Finally grind by hand
    4.Delivery against low Load gear flanks by closing discharge, valve giving approximately 15-20 psi. Noise will be eliminated 
  B) Hydraulic or Pneumatic 5. The pumped medium contains air Determine whether air is drawn through leak (see also Fault II paragraph 2&3) or whether return line is unsuitable in case of a circulating pump. In such a case it is also necessary that the return pipe terminates below liquid level.
    6.Cavitations due to  
    A) Too high suction lift. a) Reduce the suction lift.
    B) Excessive speed in the case of very viscous Liquids. b) Reduce speed. Only a low vacuum is permissible.
    C) Pumping of liquids which are highly volatile like petrol, solvents ect. Under certain circumstances liquid may require pressurization, depending on its vapour pressure
iv Motor is heating up Wrong connection of motors or only two Phases Connecting motor according to name plate and check voltages in all three phases
    3.Wrong frequency Check frequency on name plate.
    4. Pump, seizing Disconnect pressure gauge on the discharge branch and check whether delivery pressure is in accordance with the name plate of the pump.
    5.Delivery pressure too high Connect pressure gauge on the discharge branch and check whether delivery pressure is in accordance with the name plate of the pump.
    6.Viscosity too high Check viscosity at pumping temperature and compare with name plate of the pump.
    7.Mis-alignment Re-align coupling
v Fluctuating delivery 1. Frothing medium Avoid air entry in the oil (see that in the case of circulating pumps, the return line ends well below the oil level.)
VI Pump Seized 1. Excessive pressure due to wrongly adjusted relief valve Check relief valve pressure at close discharge valve, re-adjust relief valve, so that it opens approximately at 10% above working pressure.
    2.Foreign body in pumped medium Dismantle pump. Remove foreign body, Smoother seized area with oil stone, if necessary, fit new bearings and provide suction filter.
    3.Dry running Remove seized area as above. Fill with oil and wet rotors before starting up. Under certain circumstances check deaeration. (See suction1, paragraph 2.
    4.Insuffcient lubricating quality of pumped medium Check whether pumped medium has lost its lubricating properties due to elevated temperature.
If a pump has seized, gear and bearings should be dismantled. All seized areas to be smothered with oil stone. The bearing should be scraped and casting bores ground if necessary. Reassemble the pump and put it in operation initially at low pressure.
VII Relief valve chattering 1.Valve is jammed. Fit new spring, check valve for easy movement in the valve seat.


No. Name of part qty. No Name of the part qty.
1. Driver Gear with Shaft 1 11. Allan Bolt 14
2. Key 1 12. Dome Nut 1
3. Circlip 1 13. Check Nut 1
4. Oil Seal/Mech Seal 1 14. Plug 1
5. Bearings 4 15. Stud 1
6. 'O' Ring 2 16. Spring Cap 1
7. Bushes 4 17. Spring  
8. Front Cover 1 18. Valve 1
9. Main Body 1 19. Back Cover 1
10. Driven Gear with Shaft        


No. Name of part qty. No Name of the part qty.
1. Valve 1 11. Oil Seal/Mech Seal 2/1
2. Spring 1 12. Circlip 1
3. Spring Cap 1 13. Driver Gear with Shaft 1
4. Stud 1 14. key 1
5. Plug 1 15. Front Cover 1
6. Check Nut 1 16. Bushes 4
7. Dome Nut 1 17. Allan Bolt 8
8. Back Cover 1 18. Driven Gear with Shaft 1
9. Main Body 1      
10. 'O' Ring 2.      


Maintenance ?
. Periodically . Yearly . Important Points
B. Instructions ...