Possible Causes

Low volumetric efficiency (failure to deliver rated capacity and pressure)

1) Air or vapor pocket in inlet line

2) Capacity of charge pump less than capacity of power pump

3) Air or vapor trapped in or above inlet manifold

4) Air leak in liquid supply piping system

5) Loose bolts in pump inlet manifold

6) Air or gases entrained in liquid

7) Foreign object holding pump inlet or discharge valve(s)


8) Incorrect drive ratio

9) Loose belts

10) Incorrect motor or engine speed

11) Loose valve covers or cylinder head

12) Worn valves and seats

13) Safety relief valve partially open, or not holding pressure

14) Worn liners, piston rings or plungers

15) Bypass valve open, or not holding pressure

16) Blown liner gasket

17) NPSHA not sufficient

18) Liquid bypassing internally

19) Foreign object blocking liquid passage

20) Vortex in supply tank

21) Insufficient power delivered by motor


1) Inlet line partially clogged

2) Liquid vapor pressure too high

3) Liquid pumping temperature too high

4) Restricted inlet pipe fittings

5) Inlet line too long

6) Too many pipe fittings

7) Too small inlet line

8) Too low static inlet head

9) Too low atmospheric pressure

Liquid Not Delivered

1) Pump not primed

2) Air or vapor pocket in inlet line

3) Clogged inlet line

4) All inlet valves propped open

5) All discharge valves propped open

6) Loose bolts in pump inlet manifold

7) Too high valve velocities



1) NPSHA too low

2) Liquid NOT Delivered to Pump Inlet Connection

3) Excessive Stuffing Box Leakage

4) NPSHR too high

Leak at Cylinder Head or Valve Cover

1) Over Recommended Pressure

2) Loose Cylinder Head/Valve Cover

3) Damaged Gasket/O-ring

Water in Crankcase/Oil

1) Water Condensation

2) Worn seals

3) Clogged Air Breather(s)

4) Worn Crankcase Packing

5) Loose Covers

Oil Leakage from Crankcase

1) Oil Level/Temperture Too High

2) Worn seals

3) Worn Crankcase Packing

4) Loose Crankcase Cover

Excessive Heat in Power End

1) Pump Running Backward/RPM too low

2) Insufficient Oil in Power End

3) Excessive Oil in Power End

4) Incorrect Oil Viscosity

5) Operating Pump above Recommended Pressure

6) Main Bearings too Tight

7) Drive Misaligned

8) Belts too Tight

9) Discharge Valve, one or more, Stuck Open

10) Insufficient Cooling

11) Pump RPM too Low

12) Inadequate Ventilation

13) Liquid End Packing Adjusted too Tight (adjustable style packing only)

Pump Overloads Driver

1) Pump RPM too High

2) Low Voltage or other Electrical Trouble

3) Trouble with Engine, Turbine, Gear Reducer or other Related Equipment

4) Excessive Discharge Line Pressure

5) Clogged Discharge Line

6) Closed/Throttled Valve in Discharge Line

7) Incorrect Plunger/Piston Size for Application

8) Improper Bypass Conditions

9) Over-tightened Stuffing Box Glands on Adjustable Packing




Stuffing Box Leakage

1) Worn Packing

2) Worn rods or plunger

3) Worn stuffing boxes

4) Wrong size packing

5) Worn O-ring seal (replaceable boxes)

Stud Failure

1) Excessive discharge pressure

2) Improper torquing of nuts

3) Shock overload caused by pump cavitation

Excessive Valve Noise

1) Broken or weak valve spring

2) Pump cavitation

3) Air leak in inlet piping or loose bolts in pump inlet manifold

4) Air trapped above inlet valve

Inlet or Discharge Line Vibration

1) Piping inadequately supported

2) Inlet line too long or too small in diameter

3) Too many bends in inlet line

4) Multiple pump installations operating in phase

5) Obstruction Under Valve(s)

6) Packing Worn

7) Operating Above Recommended Pressure or RPM

8) Low NPSHA

Noisy Operation (Be sure to differentiate between liquid knock and mechanical knock - very few knocks are mechanical on new installations.)

1) Piston or plunger loose

2) Valve noise amplified through power end

3) Pump cavitation

4) Liquid knock

5) Air leak in inlet piping

6) Loose bolts in pump inlet manifold

7) Hydraulic noise in liquid end

8) Loose or worn crosshead pins and bushings

9) Loose connecting rod cap bolt

10) Worn connecting rod bearings

11) Worn crosshead

12) Main bearing end play excessive

13) Worn gears or chains

14) Gears or chains out of line

15) Pump running backward

16) Partial loss of prime

17) Shocks in piping system

18) Water in power end crankcase

19) Poorly supported piping, abrupt turns in piping, piping

misaligned, pipe size too small



Broken shafts, bent, stripped threads and other catastrophic failures

1) Start-up against closed gate valve in discharge line. If valve seats are discovered driven too deeply after operationof the pump, look for the following pattern of driven seats, indicative of start-up or run against a closed discharge line


Triplex single acting plunger pump:

2 inlets and 1 discharge valve seat, or

1 inlet and 2 discharge valve seats

Quintuplex single acting plunger pump:

3 inlets and 2 discharge valve seats, or

2 inlets and 3 discharge valve seats

Duplex double acting piston pumps:

2 inlets and 2 discharge valve seats

2) Low oil level

3) Contaminated oil

4) Main bearing failure

5) Piston or plunger striking cylinder head

6) Disintegration of worn valves

7) Frozen liquid in liquid body

8) Air leak in liquid supply system

9) Loose bolts in pump inlet manifold

Packing Failure

1) Normal wear

2) Improper material

3) Improper lubrication

4) Adjustable packing - gland tightened excessively

5) Dirty liquid

6) Plunger or piston rod misalignment

7) Dirty environment

Valve Failure

1) Normal wear

2) Pump cavitation

3) Abrasives in fluid

4) Incompatibility of valve components to corrosive liquid

5) Electrolysis

6) Incorrect installation - driving on the valve stem, improper torque on jam nut, valve seat and valve deck not thoroughly clean and dry when seat installed.

Plunger Failure

1) Thermal shock (cold water hitting hot ceramic plunger)

2) Packing too tight

3) Inlet valve dislocated/disassembled during pump operation

4) Stuffing box gland rubbing on plunger due to improper tightening procedure

5) Dirty liquid

6) Dirty environment



© Copyright 2008 Danco Pump & Supply Co., LTD. All Rights Reserved, 108 S. 111th E. Ave., Tulsa, OK 74128 (918) 437-8800

*Note: "Danco Pump & Supply Co. is not a licensee or in any way affiliated with National Oilwell L.P. or it's parent Company National Oilwell, Inc. and that neither National Oilwell L.P. or it's parent company National Oilwell Inc. endorses any of the products or services offered by Danco. "National Oilwell", "Gaso", "Wheatley", and "Emsco" are trademarks belonging to National-Oilwell L.P."

"Danco Pump & Supply Co. is not a licensee or in any way affiliated with Gardner-Denver® and Gardner-Denver® does not endorse any of the products or services offered by Danco. "Gardner-Denver®" and all of its pumps and parts are registered to Gardner-Denver®."

**Arrow-Engines, Kerr Engines Authorized Dealer