Gear Pumps & Motors Failure Analysis Guide

26
1. The heart of a hydraulic system is the hydraulic pump. The pump is the component that converts mechanical energy into fluid energy. A healthy pump will allow the hydraulic system on mobile equipment to perform at itsmaximum level of effectiveness FAI LU RE AN ALYSI S/ TRO U BLESH O O TI N G FAI LU RE AN ALYSI S/ TRO U BLESH O O TI N G 1 perform at its maximum level of effectiveness. Without a healthy pump, the system will be less responsive and rob the machine of performance and productivity. A properly maintained hydraulic system provides insurance that the equipment will deliver the work it is designed to do. A good preventative maintenance program affords the operator hundreds of hours of GEA R PUMPS & MOTORS GEA R PUMPS & MOTORS trouble free operation. Unfortunately, the hydraulic system does not always perform at its’ specified level. It is at these times that we need to troubleshoot the system and pinpoint the cause. A proper diagnosis is critical to providing renewed © 1998 Commercial Intertech Corp. 1 performance and extended life. This booklet is designed to help you properly identify the cause of poor performance or component failure We will be taking an in depth look at cause of poor performance or component failure. We will be taking an in-depth look at Commercial Intertech’s gear pumps and motors. Commercial Intertech is a worldwide manufacturer of fixed displacement hydraulic gear pumps and motors. With facilities on four continents Commercial is positioned to provide product and service to the global market place. For the past 75 years Commercial Intertech has been the product of choice for meeting the needs of tough mobile applications. 2 Th h t f th hd li t C ilIt t h’ t l 2. The heart of the hydraulic system, Commercial Intertech’s external spur gear pumps are a fixed displacement design. For every complete revolution of the gear shaft the pump displaces a fixed amount of oil. Pump output flow is proportional to the engine speed. There are three casting components that make up the exterior pump capsule: shaft end, gear housing, and port end cover. A tandem pump will have a fourth casting component, the bearing carrier. Various casting materials are used including gray iron (the most common), compacted graphite, ductile iron, and aluminum. G ddi h ft tf ll t l d th h d d Th t Gear and drive shafts are cut from alloy steel and then case hardened. The most common gear shaft is the integral, where the drive shaft and gear are one piece. The integral gear shaft provides exceptional torque carrying capabilities. The other type is the “continental” shaft and drive gear or the two piece. The “continental” shaft is machined with drive GEAR PUMP Shaft Thrust Plates Port End Cover extensions on both ends of the shaft; an external drive (splined or keyed) and a smaller splined end for internal drive. The drive connection inside the pump is made by Shaft End Cover Lip Seal Cover Drive Spline Drive Gear Roller Bearings Mounting Flange connection inside the pump is made by inserting the small end of the shaft into the hub of an internally splined drive gear. No matter what type of gear shaft used, the gear journals must be supported by bearings or sleeve type bushings. The roller bearing pumps require the use of ring seals to prevent the high pressure oil that lubricates the ©1998 Commercial Intertech Corp © 1998 Commercial Intertech Corp. 2 Out Board Bearing Ring Seal (High Pressure) Gear Housing Inlet Port Idler Gear bearings from traveling down the shaft. Bushing pumps do not need ring seals as the bushings are lubricated with low pressure oil. To insure maximum pumping efficiency Commercial Intertech’s pump and motor products employ the use of pressure balance thrust plates.

description

1FAI LURE AN ALYSI S/ TRO UBLESHO O TI N GGEA R PUM PS & M O TO RS1. The heart of a hydraulic system is the hydraulic pump. The pump is the component that converts mechanical energy into fluid energy. A healthy pump will allow the hydraulic system on mobile equipment to perform at its maximum level of effectiveness its’ effectiveness. Without a healthy pump, the system will be less responsive and rob the machine of performance and productivity. A properly maintained hydraulic system provide

Transcript of Gear Pumps & Motors Failure Analysis Guide

Page 1: Gear Pumps & Motors Failure Analysis Guide

1. The heart of a hydraulic system is the hydraulic pump. The pump is the component that converts mechanical energy into fluid energy. A healthy pump will allow the hydraulic system on mobile equipment to perform at its’ maximum level of effectiveness

FAILURE ANALYSIS/TROUBLESHOOTINGFAILURE ANALYSIS/TROUBLESHOOTING

1

perform at its maximum level of effectiveness. Without a healthy pump, the system will be less responsive and rob the machine of performance and productivity. A properly maintained hydraulic system provides insurance that the equipment will deliver the work it is designed to do. A good preventative maintenance program affords the operator hundreds of hours of

GEAR PUM PS & M OTORSGEAR PUM PS & M OTORS

trouble free operation. Unfortunately, the hydraulic system does not always perform at its’ specified level. It is at these times that we need to troubleshoot the system and pinpoint the cause. A proper diagnosis is critical to providing renewed

© 1998 Commercial Intertech Corp.1

performance and extended life. This booklet is designed to help you properly identify the cause of poor performance or component failure We will be taking an in depth look atcause of poor performance or component failure. We will be taking an in-depth look at Commercial Intertech’s gear pumps and motors. Commercial Intertech is a worldwide manufacturer of fixed displacement hydraulic gear pumps and motors. With facilities on four continents Commercial is positioned to provide product and service to the global market place. For the past 75 years Commercial Intertech has been the product of choice for meeting the needs of tough mobile applications. 2 Th h t f th h d li t C i l I t t h’ t l2. The heart of the hydraulic system, Commercial Intertech’s external spur gear pumps are a fixed displacement design. For every complete revolution of the gear shaft the pump displaces a fixed amount of oil. Pump output flow is proportional to the engine speed.There are three casting components that make up the exterior pump capsule: shaft end, gear housing, and port end cover. A tandem pump will have a fourth casting component, the bearing carrier. Various casting materials are used including gray iron (the most common), compacted graphite, ductile iron, and aluminum.G d d i h ft t f ll t l d th h d d Th tGear and drive shafts are cut from alloy steel and then case hardened. The most common gear shaft is the integral, where the drive shaft and gear are one piece. The integral gear shaft provides exceptional torque carrying capabilities. The other type is the “continental” shaft and drive gear or the two piece. The “continental” shaft is machined with drive

GEAR PUMPShaft

ThrustPlates Port End

Cover

extensions on both ends of the shaft; an external drive (splined or keyed) and a smaller splined end for internal drive. The drive connection inside the pump is made byShaft

End Cover Lip SealCover

DriveSpline

Drive Gear

Roller Bearings

MountingFlange

connection inside the pump is made by inserting the small end of the shaft into the hub of an internally splined drive gear. No matter what type of gear shaft used, the gear journals must be supported by bearings or sleeve type bushings. The roller bearing pumps require the use of ring seals to prevent the high pressure oil that lubricates the

©1998 Commercial Intertech Corp© 1998 Commercial Intertech Corp.2

Out BoardBearing

Ring Seal(High Pressure)

Gear Housing

Inlet Port

Idler Gearg p

bearings from traveling down the shaft. Bushing pumps do not need ring seals as the bushings are lubricated with low pressure oil.To insure maximum pumping efficiency Commercial Intertech’s pump and motor products employ the use of pressure balance thrust plates.

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TANDEM GEAR PUMPBearing carrier

Bushings

3. Tandem pumps are needed when there are multiple functions, functions that require different flows and where a single section can not provide adequate flow This P300 seriesnot provide adequate flow. This P300 series tandem pump shows the fourth casting component, the bearing carrier.

4. Both pumps and motors employ a pressure balanced thrust plate design Oil pressure

© 1998 Commercial Intertech Corp.3

Pumping Sections

balanced thrust plate design. Oil pressure hydraulically balances the thrust plates and squeezes them against the two gear faces. The squeeze provides a seal between the gear face and the thrust plate surface preventing high pressure oil from slipping back to the low pressure side of the pump. Mechanical seals are used behind the thrust plate to block oil

GEAR PUMP CUTAWAYOUT

from slipping between the plate and adjoining casting.In the roller bearing units these seals are called pocket seals and are shown in the illustration. The sleeve bearing (bushing) units use a different kind of seal called a channel seal.

INPressure Balanced Thrust Plates

5. A cross sectional view of the pumping chambers illustrates the flow path of the hydraulic oil through the gear pump. As the gears counter rotate the separating gear teeth create a vacuum drawing oil into the inlet. Oil

© 1998 Commercial Intertech Corp.4

THRUST PLATE VIEW

is picked up by each tooth and carried around the outside of the gear, oil is not drawn through the center. The pockets between the gear teeth and the housing are referred to as pumping chambers. As the gear teeth mesh on the outlet side, oil is forced out of the pockets and exits the pump.

D i h fl

Force Force

OUTPUT

Downstream resistance to the output flow causes an increase in pressure. High pressure on the outlet side of the housing forces the gears to deflect into the low pressure (inlet) side. The tips of the gear teeth contact the housing preventing high pressure output oil from leaking back to the low pressure inlet. Although necessary, this tooth to housing

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OIL FLOW

Although necessary, this tooth to housing contact can generate cast iron contaminant, particularly in new units. Therefore, Commercial Intertech 100% tests all units before shipping, bringing them up to their operating pressure. Any contaminant generated is filtered out by our test stands.

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6. Contamination is the single largest contributor to hydraulic component failures. Contamination is considered to be any substance found in the hydraulic oil not

CONTAM INATIONCONTAM INATION

substance found in the hydraulic oil not specified by the oil producer. Water, dirt, dust, air, etc.... System cleanliness and regular preventative maintenance insure a long lasting, responsive hydraulic system.

7. Particulate contamination is measured

© 1998 Commercial Intertech Corp.6

across its largest diameter to determine size. This chart shows some comparative sizes of particles in microns (or micrometers). Commercial suggests the use of a 25 micron return line filter in systems with a pressure rating of 2500 psi (172 bar) or less. In systems rated between 2500 (172 bar) and 3000 psi (207 bar) a 15 micron return line filter is

PARTICLE SIZESSUBSTANCE MICRON INCH

Grain of salt 100 .0039

Human hair 70 .0027

(207 bar) a 15 micron return line filter is recommended. A 10 micron return line filter is suggested for use with our P300 sleeve bushing pumps.

8. Particle counting is the most common

Lower limit ofvisibilty

40 .00158

White blood cell 25 .001

Talcum powder 10 .00039

Red blood cell 8 .0003

method for determining cleanliness levels of hydraulic fluids. Powerful optical instruments are used to count the number of particles in a specified volume of fluid. There are several common cleanliness level standards, of these, the International Standards Organization code has gained wide acceptance. Th ISO d i f i d b

© 1998 Commercial Intertech Corp.7

Bacteria 2 .000078

ISO CODES

The ISO code consists of two index numbers referring to the number of particles greater than 5 micrometers and 15 micrometers found in one milliliter of fluid.

Maximum recommended contamination levels are a function of component clearances and system operating pressure. As the system

ISO CODE PARTICLES/> 5 micrometers

MILLILITER> 15 micrometers

Fluid cleanlinessrequired for

18/15 2,500 320 Flow control valves,cylinders

17/14 1,300 160 Gear pumps andmotors

16/13 640 80 Directional andpressure control

pressure increases the oil film separating the working parts become thinner making the components more susceptible to damage by contaminant. Microscopic particles streaming through the hydraulic components at high velocities pound the wear surfaces weakening and eroding material. Some particles get wedged between the minute tolerances of the

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valves15/12 320 40 Vane and piston

pumps/motors14/11 160 20 Servo control valves

wedged between the minute tolerances of the new components and remove metallic material from the wear surfaces. This wear generates additional contaminant in the system and leads to leaks and a loss of component performance. Commercial gear pumps require filtration of ISO 17/14 or better.

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9. Read slide text.

CONTAMINATION

4

Effect

• Accelerated wear–bearings, thrust plates, housing

• Bearing / bushing failure• Reduced pump

efficiency

CAUSE• Improper filtration• Low oil level - concentration

of contaminant• Loose or lost breather cap• Leaking fittings, seals,

wipers

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efficiency• Reduced life• Heat• Internal leaks• Failed pump

p• Missing or collapsed inlet

strainer• Poor fill practices• Clogged filter - by-pass

10. Nuts, bolts, screws, washers, plastic closures, shop rags, pieces of hose, etc.... can cause considerable damage to hydraulic pumps and other hydraulic components. Many times the failures caused by large foreign objects occurs instantaneously as the pump ingests the debris and catastrophic failure results.

FOREIGN OBJECTFOREIGN OBJECT( NUTS & BOLTS)( NUTS & BOLTS)

11. The damage that occurred to this gear set was caused by a hardened foreign object such as a screw or nut. Additional debris has been

© 1998 Commercial Intertech Corp.10

FOREIGN OBJECTDAMAGE

generated by the broken gear teeth and component scoring. This type of failure can contaminate the entire hydraulic system.

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Page 5: Gear Pumps & Motors Failure Analysis Guide

12. Particles too large to fit between the tight component tolerances will cause surface to surface contact removing material from the softer thrust plate Damage to the thrust plateLARGE PARTICLELARGE PARTICLE

5

softer thrust plate. Damage to the thrust plate surface, which provides a sealing surface between the high and low pressure oil leads to leaks and a loss of performance. Contamination in a hydraulic system is self perpetuating. As damage to internal components continues additional debris is generated by the wearing of the components.

CONTAM INATIONCONTAM INATION

GearMotion

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Thrust plate

Large particle contaminant

13. The pump thrust plate is one of the best places to look for evidence contributing to the pump failure. The thrust plate is sometimes referred to as a wear plate. The score marks on the above plate were caused by particles being dragged across the plate surface by the hardened gear face.

SCORED THRUST PLATE

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SCORED THRUST PLATE14. New components provide a smooth, even surface allowing a continuous oil film to exist between the thrust plate and gear face. When these surfaces become scored the oil film dissipates into the grooves interrupting the film. Metal to metal contact occurs, resulting in an increase in friction and heat. The grooved plate surface can also provide an escape route for high pressure oil to go back to low pressure inlet, resulting in a loss of pumping efficiency

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pumping efficiency.

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15. P300 series plate shows score marks from large particle contaminant. SCORED THRUST PLATE

6

© 1998 Commercial Intertech Corp.1516. Microscopic particles the size of airborne

dust can accumulate in the tiny tolerances of

FINE PARTICLEFINE PARTICLECONTAM INATIONCONTAM INATION

today's hydraulic components. The accumulation can form a wedge between moving parts, increasing friction and accelerating wear. The velocity of the tiny particles striking the wear surfaces can erode material weakening the wear surface and causing spalling. This erosion of metal leads to internal leaks in critical components and

Th t l t

Fine particle contaminants

to internal leaks in critical components and adds additional contamination to the hydraulic system. All this adds up to a reduction of system efficiency causing the engine to work harder, increasing fuel consumption. Roller bearings are more susceptible to fine particle contaminant than the bushing (sleeve type). The bushing units, however, are more

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Thrust plateyp ) g , ,susceptible to large contaminant than roller bearings.

THRUST PLATE VIEW17. As the gear teeth mesh and oil is forced out of the pump outlet, a small amount of the oil is trapped by the meshing teeth in the tooth

Force Force

OUTPUT

space root area (circled). The trapped oil is forced at right angles into the faces of the thrust plates. Relieved areas on the plates called trapping grooves allow the high pressure oil to escape. The high velocity of the oil moving at a right angle to the thrust plate will do serious damage to the thrust plate in the trapping groove area if fine particle

© 1998 Commercial Intertech Corp.17

OIL FLOW

in the trapping groove area if fine particle contamination is being carried by the oil.

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18. The fine particles being carried by the hydraulic fluid erodes the thrust plate surface in the trapping groove on the high pressure side of the pump plate The erosion will be

FINE PARTICLECONTAMINATION

7

side of the pump plate. The erosion will be heaviest where the teeth mesh and then migrate towards the low pressure side of the plate. Over time, the wear cuts a channel into the plates’ surface allowing the oil to leak back to the pump inlet. The volumetric efficiency of the pump is reduced.

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19. A closer inspection of the plate surface not only reveals the damage in the center of the plate but in the root seal area as well. A light ring around the I.D. root seal area develops due to the very tight clearances. Fine particles wear the thrust plate surface leaving a polished appearance

SCORED THRUST PLATE

appearance.

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SCORED THRUST PLATE20. This P300 thrust plate shows evidence of fine particle contamination on the back side of the thrust plate. Fine erratic tracks are cut into t e t ust p ate. e e at c t ac s a e cut tothe plate surface around the balancing holes and low pressure area.

© 1998 Commercial Intertech Corp.20

Page 8: Gear Pumps & Motors Failure Analysis Guide

21. This thrust plate face shows erosion damage in the areas of high oil velocity, such as the trapping groove and balance holes. Erosion of the wear surface has also occurred

SCORED THRUST PLATE

8

Erosion of the wear surface has also occurred just below the balance hole. The metal removed from the wear surfaces adds to the contaminated condition.

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Leakage in Hydraulic ComponentsLeakage in Hydraulic ComponentsLeakage in Hydraulic Components

+ 2 Control of clearance critical

22. Internal leakage is the primary cause of a loss of performance in a hydraulic system. Of the three factors identified above, control of critical clearances have the most dramatic impact. Wear, accelerated by contamination, heat, or pressure, will act to increase these critical clearances with disastrous results.

Q =flow(leakage)

00

1

3

+L th f S l 1

© 1998 Commercial Intertech Corp.22

0 +•Length of Seal 1•Clearance 2•Pressure 3

WORN DRIVESHAFT

23. When contamination is present two wear bands will develop under the ring seals on the gear shaft of the roller bearing pumps. These bronze high pressure seals are designed to reduce the high pressure oil lubricating the bearings to low pressure before reaching the shaft seal. Tiny particles, under high pressure and velocity, progressively wear the gear journal surface until the ring seal is no longer effective. High pressure jets under the ring seal pressurizing the shaft seal area.

The oil pressure on the shaft seal can force the seal lip away from the journal or even dislodge the seal from the bore. In both instances an external leak would occur. Pump shaft seals are typically rated for a maximum pressure of 15 to 20 psi. Shaft seals are sensitive to shaft speed, an increase in speed can cause a decrease in the maximum pressure rating of the seal. 23

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24. When a seal leak is discovered the first inclination for the maintenance staff can be to replace the shaft seal. This will not solve the problem. The gear set and ring seals may also

DRIVE SHAFT RING SEAL

9

p g g yhave to be replaced. A rule of thumb for determining excessive wear on the shaft is that if you can feel the wear with your finger nail it should be replaced. Ring seals are not needed in the bushing pumps as the bushings are lubricated with low pressure inlet oil.

© 1998 Commercial Intertech Corp.24

25. Contamination has caused wear bands to develop on this roller bearing motor gear. Closest to the spline end, the shaft has been grooved by dirt trapped under the lip seal. As the damage progresses external shaft seal leaks will develop. Replacing the shaft seal at this point will not correct the leak as the undercut

MOTOR SHAFT

will prevent the proper squeeze of the seal on the shaft. Note: The contamination attacking the shaft seal area could also been brought in from the outside environment.

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CAVITATION &CAVITATION &AERATIONAERATION

26. Excessive noise in a hydraulic system can be caused by the presence of air in the hydraulic oil. Air can be introduced into the

AERATIONAERATION system two ways; through cavitation or aeration. “Cavitation” occurs when the pump inlet flow can no longer fill the pump chambers created by the separation of the gear teeth. The partial vacuum vaporizes some of the oil causing air and or water to come out of solution. C it ti i th f ti f i d t

© 1998 Commercial Intertech Corp.26

Thrust plate

Cavitation is the formation of air, and water or oil vapor bubbles in the hydraulic oil. Aeration is a form of cavitation that occurs when outside air is drawn into the hydraulic system due to a loose fitting or low oil level in the reservoir.

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27. As the bubbles, created by cavitation and aeration, are carried around to the pump outlet, the increase in pressure squeezes the bubbles.

CAVITATION &CAVITATION &AERATIONAERATION

10

An implosion occurs when the pressure becomes too great and the bubbles collapse inward.

AERATIONAERATION

© 1998 Commercial Intertech Corp.27

Thrust plate

28. When the air bubbles implode intense shock waves bombard the surface of the wear plates. The shock waves erode the plates’ surfaces on the high pressure side and trapping groove area. The sealing capability of the plate is reduced resulting in a loss of output flow.

CAVITATION &CAVITATION &AERATIONAERATION

The presence of air can also reduce the volume of oil available to carry away heat that is produced by mechanical friction. Vacuum conditions created in the pump rob oil from the bearing and thrust plate areas. The loss of oil in bearing bore upsets the loading which can result in premature bearing failure. Thrust

l t l i th il t i t i th i Thrust plateplates, relying on the oil to maintain their balance become unbalanced, resulting in a milling of the plate surface.Physical damage can also be seen on the gear housing bore in the form of a rough surface in the gear wipe area.

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p

CAVITATION DAMAGECAVITATION DAMAGE

Effect• Noise• Heat• Accelerated wear

– thrust plates / housing• Internal leaks• Reduced pump

CAUSE - Inlet restriction• Clogged inlet strainer /

breather• Inlet strainer too small• Inlet line too long• Inlet line bore too small

29. Read slide text.

© 1998 Commercial Intertech Corp.29

educed pu p efficiency• Erratic actuator performance• Failed pump

• Excessive engine speed• Collapsed inlet hose• Suction head too great• Oil too viscous (cold weather)

Page 11: Gear Pumps & Motors Failure Analysis Guide

30. Read slide text.AERATION DAMAGEAERATION DAMAGE

11

Effect• Noise• Heat• Accelerated wear

– thrust plates / housing• Internal leaks• Erratic actuator performance

CAUSE - Air enters oil• Low oil level• Vortexing of oil above

strainer - whirlpool• Loose inlet fittings• Worn pump shaft seal• Worn cylinder rod seal

© 1998 Commercial Intertech Corp.30

p• Reduced pump efficiency• Failed pump

Worn cylinder rod seal• Foam suspended in oil due

to sloshing in the reservoir

CAVITATED THRUST PLATE31. This plate has been damaged by cavitation. As the gear teeth come around to the discharge side of the pump (outlet) the oil is exposed to the outlet pressure collapsing the large air bubbles.

OUTLET

INLET

© 1998 Commercial Intertech Corp.31

CAVITATED THRUST PLATE32. A close up of the plate shows the severity of the pitting. The damage is heaviest in the root seal area where the clearance between the plate and the gear face is the tightest. This damage allows high pressure oil to escape down the gear journal into the bearing or bushing.

© 1998 Commercial Intertech Corp.32

Page 12: Gear Pumps & Motors Failure Analysis Guide

33. Motor cavitation occurs when the supply pump cannot produce enough flow to keep up with the speed of the motor. The

CAVITATED MOTORTHRUST PLATE

12

motor then begins to act as a pump. This M75 series motor plate has cavitation damage on both sides of the plate. This condition occurs when a motor is cavitated in both directions of rotation. The damage to this plate is heaviest in the trapping groove areas because the

it ti b bbl t d th idcavitation bubbles created on the pump side of the motor are carried to the outlet side and are mechanically imploded by the meshing of the gear teeth.

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34. Again, a close up shows the severity of the damage. CAVITATED MOTOR

THRUST PLATE

35. A loss of lubrication in the pump can also cause rifling of the gears and thrust plates. Air in the system creates an imbalance in the thrust plate forcing it to

© 1998 Commercial Intertech Corp.34

RIFLED GEAR& THRUST PLATE

imbalance in the thrust plate forcing it to come in harder over one gear than the other. The gears try to separate and walk towards opposite ends of the pump. The effect is a milling of the plates behind the idler gear at one end of the pump and the drive gear on the other end. The torque needed to drive the pump increases dramatically and the pump becomes heated. The removal of thrust plate material will contaminate the hydraulic system.Note: The problem described above has been largely eliminated in the P300 series bushing pumps because of the new thrust plate design. However, all pumps with an integral d i h ft (i l di th P300 i )

© 1998 Commercial Intertech Corp.35

drive shaft (including the P300 series) are susceptible to rifling if an external force is applied to the drive shaft (push or pulling force). An example of this is an interference fit between the drive shaft and its drive coupling.

Page 13: Gear Pumps & Motors Failure Analysis Guide

36. Milling damage is evident at the center of this thrust plate. Not as obvious is the cavitation erosion on the plate at three o’clock. RIFLED THRUST PLATE

13

37. The milling has not erased the tell tale erosion damaged caused by the cavitation. When the damage has progressed to this point the entire hydraulic system should be flushed and the filters and strainers checked.

© 1998 Commercial Intertech Corp.36

38. Pressure and hydraulic shock are also causes of pump failure. Pumps operating under a continuous heavy load, (high pressure), and extended duty cycle are susceptible to premature wear and failure. F t d b th tl t

RIFLED THRUST PLATEForces generated by the pump outlet pressure and gear area causes a deflection of the gears. This stresses the bearings or bushings that support the gear journals. The oil film needed to lubricate and cushion the pump elements becomes thinner and thinner with the increase in pressure until direct contact is made. In the roller bearing pump the repeated heavyIn the roller bearing pump the repeated heavy loading fractures the hardened surfaces of the needle bearings, bearing race, and gear journals. These fractures, over time, lead to a breakdown of the surface material. Small pieces of material break away leaving a rough running surface. The rough surface can no longer support the film of oil needed to

© 1998 Commercial Intertech Corp.37

PRESSURE DAM AGE

lubricate and cushion the pump components. The damage quickly accelerates until a catastrophic failure occurs spreading contaminant throughout the hydraulic system. The bushing pumps rely more heavily on the film of oil to support the loaded gear journal. Clearances between the journal and bushing

f h h l i hPRESSURE DAM AGEPRESSURE DAM AGE

REPEATEDHEAVY

LOADING

surface are greater than the clearance in the bearing pumps. This is necessary to support the thicker oil film. When subjected to repeated heavy loads a breakdown of the oil film allows direct contact of the bushing and journal. The PTFE coating, that protects the bushing I.D., wears away and an increase in friction and heat occurs. The bushing surface

©1998 Commercial Intertech Corp.

LOADING

38

ct o a d eat occu s. e bus g su acebecomes rough and the oil film can no longer be supported. Under continued operation and friction becomes severe and the bushing may start spinning in the bore. Again a catastrophic failure results contaminating the entire hydraulic system.

Page 14: Gear Pumps & Motors Failure Analysis Guide

39. Read slide text.

PRESSURE DAMAGEPRESSURE DAMAGE

14

CAUSE

• Improper relief valve setting• Relief valve malfunctioned• Slow acting relief valve• Absence of a relief valve• Improper size elbow or fitting

EFFECT• Accelerated wear • Cracked housings• Excessive housing cut-out• Reduced efficiency• Internal leakage

Bearing / bushing failure

©1998 Commercial Intertech Corp.

Improper size elbow or fitting downstream of the valve affecting the relief valve performance

• Bearing / bushing failure• Thrust plates coined, warped or cracked• Broken drive / connecting shaft

39

BEARING FAILURE40. Extended operation under high pressures has caused the spalling of the needle bearings in this bearing. Surface cracks have lead to a fracturing of the needle bearing material. An increase in system noise and heat could alert the operator to this type of problem.

©1998 Commercial Intertech Corp.40

BEARING FAILURE41. This slide shows the inner race of the bearing and the damage caused by excessive loading.

©1998 Commercial Intertech Corp.41

Page 15: Gear Pumps & Motors Failure Analysis Guide

42. As the bearing wears the gear journal becomes damaged by the direct contact of the journal to the needle bearings.

BEARING FAILURE

15

©1998 Commercial Intertech Corp.42

43. The system pressure deflects the gears into the low pressure inlet side of the pump. If the system pressure increases above the pressure rating of the pump, then the gears deflect too far and the gear housing cut-out becomes excessive. Internal slip increases and the pump becomes less efficient. The contaminant created by the

PRESSURE DAMAGEDGEAR HOUSING

cut-out can foul relief valves and other system components. If the housing cut-out exceeds .005” (.007” for a bushing pump gear housing) the gear housing should be replaced.

©1998 Commercial Intertech Corp.43

PRESSURE DAMAGEDGEAR HOUSING

44. Hydraulic shock loads can cause an immediate component failure in your hydraulic system. Sudden pressure spikes that exceed the pressure rating of the pump can crack theGEAR HOUSING pressure rating of the pump can crack the housing at the port location and bolt hole areas of the casting. A slow acting or malfunctioning relief valve can cause excessive pressure spikes in the system.

©1998 Commercial Intertech Corp.44

Page 16: Gear Pumps & Motors Failure Analysis Guide

45. Commercial Intertech’s engineering department sets maximum pressure limits for all pumps by calculating bearing loads and housing stresses However the larger the port

PRESSURE DAMAGEDGEAR HOUSING

16

housing stresses. However, the larger the port size in the gear housing the weaker the casting. The larger port requires the removal of a greater percentage of casting material and a reduction in the safety factor. Continuous operating pressures above the pump rating can lead to cracked housings due to fatigue.

©1998 Commercial Intertech Corp.45

PRESSURE DAMAGEDTHRUST PLATE

46. Thrust plates can also be damaged by excessive pressure. The above plate split through the middle due to excessive loads. The thrust plates used in the roller bearing product are most susceptible to damage between the two gear bores. A small bleed hole, needed for balancing pressures in the bearing bores, is machined on the back side of the plate in this area. Couple this with fact that the greatest pressure in the pump occurs at the center of the plate where the gear teeth mesh. The oblong bores in the above plate are due to a bearing failure.

©1998 Commercial Intertech Corp.46

HEAVILY COINED THRUSTPLATE

47. Excessive pressures can also cause coining damage to the thrust plate. This is a deformation of material on the low pressure inlet side of the plate The heavy loading PLATEinlet side of the plate. The heavy loading pushes the plate into the gear housing with enough force to cause a bulging of material in the relieved edge of the plate. The major O.D. is flattened.

©1998 Commercial Intertech Corp.

COINING

47

Page 17: Gear Pumps & Motors Failure Analysis Guide

48. Hydraulic shock and excessive pressure can also cause failures to the pump drive line. Many times the drive coupling or pump drive shaft will fail In the above example the pump

PRESSURE DAMAGEDDRIVE SHAFT

17

shaft will fail. In the above example, the pump drive shaft broke where the shaft diameter is the smallest. The drive shaft was not strong enough to withstand the torque load generated by the high pressure. Each section of a multiple pump or motor should be regarded as a single unit with corresponding delivery and power input p g y p prequirements. Since the entire input horsepower required to drive the pump is fed through a common drive shaft, the power delivered to or from the unit is limited by the physical strength of the shaft. This limit is defined as a “PL” factor; “P” being the maximum operating pressure and “L” the

©1998 Commercial Intertech Corp.48

summation of gear widths “PL” for a single unit is calculated by multiplying thesummation of gear widths. PL for a single unit is calculated by multiplying the maximum operating pressure by the gear width. Each style or type of shaft has a unique “PL” rating. Tables are provided in each of the pump/motor product catalogs defining the “PL” rating for each shaft type. If the “PL” factor exceeds the catalog rating of your shaft choice select a new shaft type with an adequate “PL” rating.

PL= Pressure X Total Gear Width

Torsional fatigue can also cause a shaft to fail, having a similar appearance to the above shaft. With torsional fatigue failure, however, the core of the shaft across the break has a smeared appearance caused by repeated forces and a gradual wearing out of the shaft. (A sudden break is characterized by a rough granular shaft core.) Torsion forces acting on the shaft in the same direction tend to cause a break at a 450 angle to the shaft axis.

PRESSURE DAMAGEDCONNECTING SHAFT

49. The connecting shaft in a tandem pump has the smallest diameter in the pump drive line, many times making it the weak link. In multiple units the “PL” must be calculated for the first connecting shaft as well as the gdrive shaft. When calculating the “PL” for the connecting shafts, the drive gear is not included. The calculation is made from the first connecting shaft back.

©1998 Commercial Intertech Corp.49

Page 18: Gear Pumps & Motors Failure Analysis Guide

50. Drive line misalignment can cause the pump shaft to flex with each revolution, often resulting in a clean break at a 900 angle to the shaft axis The fractures typically occur in

ROTATIONAL BENDINGFATIGUE FAILURE

18

shaft axis. The fractures typically occur in areas where stresses are concentrated, such as, holes, grooves, and reduced diameters. A rough spot on thesmooth shaft core is where the shaft finally severed.

51. Heat is generated in a hydraulic system

©1998 Commercial Intertech Corp.50

whenever oil dumps from an area of high pressure to low pressure without doing mechanical work. Oil blowing over a relief valve or flowing through piping, a valve, a clogged filter or strainer all are examples of sources of heat. Proper reservoir size can dissipate much of the heat generated in a system On some applications an oil cooler

HEATHEATHEATsystem. On some applications an oil cooler must be added to sufficiently cool the oil. Other factors, such as, contamination, cavitation/aeration, improper oil viscosity can add to the heating problems of a hydraulic system. Heat build-up causes the hydraulic oil to loose its viscosity resulting in an oil that no longer

• THINS THE SYSTEM OIL- increasing friction

• ACCELERATES THE BREAKDOWN OF THE OIL- causing sludge to form

• CAN BE CAUSED BY WORN COMPONENTS• EVERY 18°F RISE IN OIL TEMPERATURE

- doubles the rate of corrosion on exposed surfaces

y g gmeets specification. This greatly reduces the lubricating effects of the oil on the close tolerance parts. The heated oil oxidizes, encouraging corrosion, leakage, and the development of sludge. Sludge can clog filters and strainers compounding system problems. leading to cavitation and additional heating of th il

©1998 Commercial Intertech Corp.51

the oil.The close running tolerances of the pump/motor components makes them susceptible to heat damage. Add the fact that the thrust plates are being squeezed against the gear faces with hydraulic pressure; a loss of lubrication between the two surfaces can quickly lead to an increase in heat due to

HEAT DAMAGEHEAT DAMAGEquickly lead to an increase in heat due to friction.

CAUSE• Low oil level• Cavitation / aeration / water• Contamination• Inlet restriction• Relief valve• Incorrect fluid

EFFECT

• Breakdown of oil• Loss of lubricity • Accelerated wear • Reduced efficiency• Leakage• Varnish / sludge

52. Read slide text.

©1998 Commercial Intertech Corp.

• Poor reservoir design• Undersized fittings, hoses, components

• Varnish / sludge• Internal seal destruction • Seizure

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Page 19: Gear Pumps & Motors Failure Analysis Guide

53. With the loss of lubrication the thrust plate becomes heated rapidly. If the condition persists the plates will become so heated that lead in the

HEAT DAMAGEHEAT DAMAGE

19

alloy will be drawn out of the plate. HEAT DAMAGEHEAT DAMAGE

GMotion

GMotionMotionLead

©1998 Commercial Intertech Corp.

Thrust plate

GearGearGearLead

53

54. As the lead comes to the surface the trailing gear tooth smears the lead over the surface of the plate. The plate will become blackened by the lead oxidation. HEAT DAMAGEHEAT DAMAGE

GearMotion

©1998 Commercial Intertech Corp.

Thrust plate54

HEAT DAMAGED THRUSTPLATE

55. The thrust plate in this slide has been subjected to extreme heat causing the lead to be drawn to the surface. A blackened surface and thermal cracks in the plate can result.

©1998 Commercial Intertech Corp.55

Page 20: Gear Pumps & Motors Failure Analysis Guide

56. Excessive heat can cause a thrust platematerial to become brittle and crack. HEAT DAMAGED THRUST

PLATE

20

PLATE

©1998 Commercial Intertech Corp.56

HEAT DAMAGED THRUSTPLATE

57. This P300 series thrust plate has been damaged by extreme heat due to a loss of lubrication. The surface is blackened

©1998 Commercial Intertech Corp.57

HEAT DAMAGED THRUSTPLATE

58. Temperatures of 400 degrees Fahrenheit will melt the glass filled nylon channel seal used in the P300 series The buna element of PLATEused in the P300 series. The buna element of the two piece channel seal and the buna pocket seal will be damaged at a much lower temperature.

©1998 Commercial Intertech Corp.58

Page 21: Gear Pumps & Motors Failure Analysis Guide

59. With excessive heat the ends of the gear teeth near the gear face become discolored. The high heat causes a bluing of the teeth. With continued operation the gear face and

HEAT DAMAGED GEAR

21

With continued operation the gear face and thrust plate will start to weld together. The continued motion of the gear tears thrust plate material from the plates surface. The friction can generate enough heat that the pump could eventually seize up.

©1998 Commercial Intertech Corp.59

HEAT DAMAGED THRUSTPLATE

60. Welding between the gear face and the thrust plate has occurred resulting in a ripping of material from the plate surface.

©1998 Commercial Intertech Corp.60

FRETTING DAM AGEFRETTING DAM AGE

61. Fretting is a condition that occurs between the drive shaft extension and the drive coupling. These parts are commonly lubricated with a heavy grease. Fretting

FRETTING DAM AGEFRETTING DAM AGE

CouplingSmall amplitude

vibration

damage occurs when the grease picks up grit and the small amplitude vibration makes the contaminated grease act like sandpaper. As the wear progresses the clearance between the parts becomes greater allowing more shaft coupling movement. The wear accelerates until there is not enough engagement to carry the torque load put on the shaft At this point

©1998 Commercial Intertech Corp.

Contaminantsuspendedin grease

Drive spline

61

the torque load put on the shaft. At this point the coupling will spin on the shaft stopping the revolution of the pump gears and thus pump flow. The coupling and the pump gear set will have to be replaced.

Page 22: Gear Pumps & Motors Failure Analysis Guide

62. This splined drive shaft has been worn by fretting corrosion. To prevent this damage the drive coupling should be cleaned regularly followed with the application of a light coat of

22

FRETTED DRIVESHAFTfollowed with the application of a light coat of synthetic grease.

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REBUILD ERRORSREBUILD ERRORS

63. Commercial Intertech performs a break-in test on 100% of it’s factory built pumps. Any pump repaired and rebuilt should also be tested. This gives the unit a proper break-in and insures that it is performing to specification. The unit should also be inspected for external leaks at this time. The recommended test/break-in procedure is described in all the Commercial Intertech pump service manuals. Fact, 99% of all rebuild errors can be found at the test stand.

©1998 Commercial Intertech Corp.63

POTENTIAL ASSEMBLYERRORS

POTENTIAL ASSEMBLYERRORS

64. Read slide text.

ERRORSERRORSCAUSE• Improper bolt torque• Nicked lip seal• Pinched / fretted section seal• Improper installation of

EFFECT

• Heat• Extruded section seal• External leak• Internal leak

R d d ffi i

©1998 Commercial Intertech Corp.

p p thrust plate• Pinched pocket / channel seal

• Reduced efficiency

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Page 23: Gear Pumps & Motors Failure Analysis Guide

65. Pinched or fretted section seals can lead to external leaks. If the section seal is not properly installed the seal can be flattened between the mating castings This provides a

PINCHED & FRETTEDSEALS

23

between the mating castings. This provides a leak path for oil to escape.

©1998 Commercial Intertech Corp.65 ©1998 Commercial Intertech Corp.

SYSTEM

66. Your approach to system maintenance will either give you a reliable, relatively trouble free system or a system that is a constant maintenance nightmare.The best advise we can offer is to meet or exceed the Original Equipment M f t ’ d ti

SYSTEM MAINTENANCESYSTEM MAINTENANCE

SYSTEMMAINTENANCE

Manufacturer’s recommendations on maintenance intervals, and follow his recommendations when replacing critical system components.The OEM has engineered and assembled a hydraulic system which has been thoroughly tested and proven to give the best performance possibleperformance possible.

©1998 Commercial Intertech Corp.66

THE SYSTEMTHE SYSTEM67. These are critical system components.

THE SYSTEMS S

INCLUDES:• Hydraulic Oil• Hoses/tubing• Fittings

• Hydraulic Pump• Directional Valve• Actuator

©1998 Commercial Intertech Corp.

g• Filters – motor

– cylinder

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Page 24: Gear Pumps & Motors Failure Analysis Guide

68. Careless substitution of any critical system component with a substandard replacement will lead to extended downtime and unnecessary expense

SUBSTITUTIONSSUBSTITUTIONS

24

unnecessary expense.

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69. Read slide text.

HYDRAULIC OILHYDRAULIC OIL

• Follow OEM recommendations as• Follow OEM recommendations as closely as possible• Unnecessary additives may be detrimental• Do not mix and match

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WHEN REPLACINGWHEN REPLACINGHOSES LINES & FITTINGSHOSES LINES & FITTINGS

70. Read slide text.

HOSES, LINES & FITTINGSHOSES, LINES & FITTINGS

Use products with the same:– Size– Material– Length

Pressure rating

©1998 Commercial Intertech Corp.

– Pressure ratingas the original equipment

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Page 25: Gear Pumps & Motors Failure Analysis Guide

71. Using “after market” hydraulic components can be a dangerous proposition.HYDRAULICHYDRAULIC

COMPONENTSCOMPONENTS

25

S

After market substitutions may lack proper:• Tolerances• Testing• Pressure rating• Safety factor

M t i l

©1998 Commercial Intertech Corp.

• Material• Design

71

72. SUBSTITUTES CAN COST YOU BIG: • added downtime! • additional repairs !!• additional cost!!!

SUBSTITUTIONS CAN DEALSUBSTITUTIONS CAN DEALYOU A LOSING HANDYOU A LOSING HAND

©1998 Commercial Intertech Corp.72

73. Replacing a worn or failed pump/motor without taking the proper precautions can lead to rapid failure of the new unit. The

PUM P / M OTORPUM P / M OTORREPLACEM ENTREPLACEM ENT

tight factory tolerances of a new unit make it more susceptible to the same conditions that caused the first unit to fail. Flushing the hydraulic system, changing filters, and replacing used oil with new can insure proper component life. The relief valve and the governor should be reset prior to resuming normal operation

©1998 Commercial Intertech Corp.73

normal operation.

ALWAYS USE AN ACCURATE GAGEWHEN ADJUSTING THE RELIEFVALVE PRESSURE SETTING.

Page 26: Gear Pumps & Motors Failure Analysis Guide

74. Before installing a new or rebuilt pump or motor, back off the main relief valve until the spring tension on the adjusting screw is relieved. This will avoid the possibility of immediate

RECOMMENDED START-UPRECOMMENDED START-UPFOR NEW OR REBUILT PUMP/FOR NEW OR REBUILT PUMP/

26

This will avoid the possibility of immediate damage to the replacement unit in the event that the relief valve setting had been increased beyond the recommended operating pressure prior to removing the old unit.Before connecting any lines to the pump or motor, fill all ports with clean oil to provide initial lubrication. This is particularly important

MOTORMOTOR• Insure system cleanliness• Back-off relief valve pressure and reset governor• Fill unit with clean oil before connecting lines• Connect the lines and mount unit• Operate the unit at zero pressure for a minimum ofp y p

where the unit is located above the oil reservoir.During the break-in period, the unit should run free and not develop an excessive amount of heat. Commercial’s pump/valve units should be started up in the shift to raise position. This will insure a good prime and prevent heat damage. ©1998 Commercial Intertech Corp.

two minutes at low speed• Gradually increase speed and pressure to normal operating conditions - approximately 5 minutes• Reset the main relief valve while the unit is operating at maximum operating speed

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Commercial Intertech one of the world’s largestCommercial Intertech, one of the world s largestmanufacturers of hydraulic components for the

mobile market, has brought you this training programon Failure Analysis. If you have any further questions

on this subject or any of our hydraulic products,please contact your Commercial Intertech Sales

Representative or your nearest AuthorizedDistributor.

©1998 Commercial Intertech Corp.75