MRO Today - You're so vane

You’re so vane

Maintaining, troubleshooting and repairing vane pumps

by Douglas Bougher, Product Manager, Eaton Corp.

Vane-type pumps and motors are some of the most commonly used components in mobile and industrial hydraulic systems. They are efficient, economical and reliable. But, like all mechanical devices, they are neither maintenance-free, nor indestructible.

In more than 75 years of designing and building vane-type pumps and motors, Vickers engineers have encountered virtually every “innovative” way devised by end users to destroy them. The lessons learned can be condensed into a simple rule, which, if followed, will ensure maximum life for your pump or motor.

The golden rule
Keep the fluid clean! Dirty hydraulic fluid is the root cause of 80 percent or more of all hydraulic systems problems, and it’s the first thing you should look for when a problem occurs. Eliminating contamination should be one of the primary focuses of your maintenance program.

Fluid contamination comes from four basic sources:
    • Contaminated new oil
    • Built-in contamination
    • Ingressed contamination
    • Internally generated contamination

Contaminated new oil
Although hydraulic and lubrication fluids are produced under relatively clean conditions, they travel through many hoses and pipes before being stored in drums or a bulk tank at your facility. At this point, the fluid is no longer clean because the fluid lines it has traveled through have contributed metal and rubber particles, and the drums have added flakes of metal or scale. These contaminants should be removed from new fluids with a portable transfer cart fitted with a high efficiency filter.

Built-in contamination
New machinery always contains a certain amount of built-in contamination. The amount of contamination removed during the system flush depends not only on the effectiveness of the filters used, but also the temperature, viscosity, velocity and “turbulence” of the flushing fluid.

Irrespective of the standard of flushing done by the machine builder, an off-load period of “running-in” should be regarded as essential for any new or rebuilt hydraulic system.

Ingressed contamination
Contamination from the immediate surroundings can be ingressed into the fluid power or lubrication system. The key here is to severely limit the opportunities for contaminants to enter the system. There are four major ways dirt can enter a system:
    • Reservoir vent ports (breathers)
    • Power unit or system access plates
    • Components left open during maintenance
    • Cylinder seals

Generated contamination
The most dangerous contamination to a system is generated by the system itself. These particles are “work-hardened” to a greater hardness than the surfaces from which they came, and are very aggressive in causing further wear in the system. If they are not quickly captured, the elevated contamination levels will cause the number of additional generated particles to increase at an accelerated rate. The best way to prevent this is to start with a clean (fully flushed) system and keep the system fluid clean.

How clean is clean?
Designing and maintaining an optimal filtration system for a specific application is beyond the scope of this article. A number of good references are available from filtration, fluid and equipment suppliers, who all are willing to provide technical assistance and support. One such manual is Eaton’s “Guide to Systemic Contamination Control,” available for free downloading at http://hydraulics.eaton.com/products/filtration.htm.

Figure 1: A chopped ring caused by particulate damage to the hydraulic fluid.

Figure 2: Cavitation has caused pitting of the surface of this flex plate.

Figure 3: This flex plate has a metered edge due to erosion.

Troubleshooting
Since 80 percent of all hydraulic system problems are directly traceable to contaminated fluids, it makes sense to begin troubleshooting by learning to identify contaminant damage. Fortunately, it’s generally quite easy to spot because it produces physical changes in system components that you can easily see.

For example, if you see marked or “frosted” vanes, grooves cut into the shaft seal diameter, or a “chopped” ring (Figure 1), you can be pretty sure the culprit is particulate contamination of the hydraulic fluid. You then have to find the source of the contamination and eliminate it before you repair the pump or motor, flush the system, and put it back into operation.

Cavitation damage
Cavitation occurs when bubbles form and collapse within the fluid. The bubble generates very high temperatures that eventually erode the surfaces within the device. The bubbles may be from air that’s trapped in the fluid or from the fluid being literally “pulled apart” by forces within the system to form voids that then collapse.

Damage caused by the implosion of trapped air usually takes the form of surface pitting as shown in Figure 2.

Typical causes of this kind of damage:
    • Suction line allowing inlet of air
    • Shaft seals worn, allowing ingestion of air
    • Reservoir problems
    • Low oil level
    • Poor baffling
    • Reservoir inlet too high
    • Reservoir too small
    • Unsuitable fluid

Damage caused by fluid void implosions can be quite severe. Typical causes of this kind of damage include:
    • Inlet velocity too fast
    • Reservoir / system design
    • Clogged inlet strainer/filter
    • Restricted fluid flow
    • High water content in oil
    • Running the pump over recommended rpm

Erosion damage
Although some damage can look a lot like cavitation, it may actually be caused by particulate contamination in a high-speed oil stream. This kind of damage is typically found at metering edges or critical surfaces and tends to produce less extensive damage than cavitation.

The causes include either contaminated oil, or oil above the recommended ISO level.

Catastrophic damage
There are many other ways to damage a pump or motor, including over-pressurization, air locks, misalignment, and a whole range of improper modifications, component misapplications and incorrect assembly procedures. What these all have in common is that they tend to produce catastrophic failures that are easy to see and diagnose.

Vane pump repair
One of the great advantages of vane-type technology is the relative ease with which pumps and motors using it can be altered and repaired in the field.

Virtually all modern designs place the critical operating components in a cartridge that is easily removed and replaced as a unit. The displacement of a cartridge-type vane pump can be changed over a significant range by simply changing cartridges as well.

In most cases, an overhaul consists of disconnecting the pump or motor from the equipment it’s attached to, removing a few bolts, and sliding the cartridge out. At that point, the bearings and seals can be replaced, and the cartridge replaced with a new unit and reinstalled.

Cartridges can also be rebuilt in the field. It is important to use only genuine replacement parts when rebuilding a cartridge. Imitation or “will fit” parts can significantly shorten the life of a pump or motor, and may fail catastrophically, damaging other system components in the process.

If you rebuild it...
All pump manufacturers provide rebuild kits for their products and detailed instructions for the operation. A typical example of an overhaul manual can be found at http://hydraulics.eaton.com/products/pdfs/i3143s.pdf.

Unless the pump or motor has failed catastrophically, a field overhaul with genuine OEM parts will quickly return it to service with performance equal to a new unit.

The key to avoiding that catastrophic failure is maintenance, and the Golden Rule of pump maintenance is KEEP THE FLUID CLEAN. Do what’s necessary to make that happen, and vane pump troubleshooting and repair will make up a very small part of your workday.

Douglas Bougher is product manager – vane products, for Eaton Corporation, Eden Prairie, Minnesota.

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