Pumping out useful information

Industrial pumps represent a significant capital cost, so it is important, to ensure they run efficiently and reliably: Colin Chapman of Henkel provides advice regarding assembly and repair.

Many pump breakdowns are the result of needless failures.

For example, the loss of clamp loads between assemblies can be caused a loose fastener.

A small part - but it can cause a huge problem.

That's because the result can be misalignment and subsequent bearing failure.

And that can be costly.

Yet by following some simple procedures during initial assembly - and then carrying out proactive maintenance - the risk of such incidents occurring can be significantly reduced.

In fact, the use of appropriate products at assembly stage can make disassembly that much easier when it comes to carrying out those maintenance tasks.

Take, for instance, bearing frames and housings.

The air space between threads on drain plugs, oiler nipples and other fittings can allow lubricants to weep out.

However, the use of an anaerobic thread sealant can provide a ready solution.

Anaerobic products are liquids that cure on metal surfaces in the absence of air.

That means the act of tightening mated threaded components will start the curing process and thus cause a firm seal to be created.

In turn, this will provide an impenetrable seal that will keep out moisture and corrosion and keep in the lubricant.

Despite the sure seal, the joints can be disassembled using normal hand tools for maintenance purposes.

The results include less oil consumption, elimination of seized fittings and removal of potential hazards caused by spillage.

Anaerobics - this time in the form of threadlockers - can be used to prevent leaks and seizures between bearing housings and oil seals.

As with any press fit, there are small air spaces that have the potential to create leak paths.

But by filling those spaces with a threadlocking adhesive - either in liquid of semi-solid stick form - applied to the outside diameter of the oil seal the problem can be avoided.

Threadlocking adhesives can also be used during pump assembly to prevent leaks and seizure between frame adapters and oil seals, and stop the loosening of mounting bolts, gland studs and pump casing bolts.

In addition, they can prevent wear by securing keys into keyways and stop disengagement, damage or misalignment in couplings caused by component movement or loosening.

Wherever a traditional gasket is used on a pump, an anaerobic flange sealant can be employed as a replacement.

Not only does the use of a liquid product eliminate the need for a vast range of different sized gaskets being held in stock, but it also means that failures due to compression set, shrinkage, relaxation and breaks can be avoided.

A constant clamp is ensured and, because the sealant flows into any surface imperfections, there is a constant, reliable seal.

Once more, because flange sealants are anaerobic, the product can be applied as a liquid or a semi-solid stick, but curing will not take place until air is removed by the surfaces being brought together.

Of course, bearings are prone to spinning on their shafts or within their housings, resulting in damage to these parts.

And that can occur whatever the fitting method - press, shrink or slip.

The use of a retaining compound on the outside diameter of the outboard bearing or the inside diameter of the inboard bearing means that the chance of damage is reduced - and in many most cases, eliminated.

Retaining adhesives fill every gap between mating surfaces.

This means 100% surface contact between mating parts is achieved - resulting in superior joint strength.

The fact that adhesives cover the entire surface area also means that the joint is effectively sealed against corrosive forces in the atmosphere.

Like many other anaerobic adhesives, retainers come in liquid or stick form.

Any exposed metal part on a pump that is not stainless steel or coated is subject to rust.

And where rust forms, failures will eventually occur.

Yet by applying a suitable antiseize product during assembly not only will moisture be prevented from entering a joint, but the fasteners will be easier to undo for maintenance purposes.

Typical applications involving pumps include power end and clamp bolts, lock nuts, dowel pins on bearing frames, shaft impellers and gland nuts.

Antiseize is also used to prevent the frame adapter, stuffing box and casing from seising together.

Alongside traditional antiseize pastes, these products are now available in stick form.

Turning to the maintenance of industrial pumps, it is obvious that the same products can be used to meet a variety of needs.

However, there are some additional options that can be considered.

Minor worn areas of casings, cutwaters, wear ring seats, vane tips or impellers can be readily rebuilt by means of products like ferrosilicon or ceramic fibre filled repair epoxies or wearing compounds.

After abrading and cleaning the surfaces under repair, the products are simply mixed and applied according to instructions.

A coat of a brushable ceramic white is then applied and, once gel time is reached, a second layer, this time a ceramic grey, is brushed on to a minimum thickness of 0.5mm.

Worn shafts can be restored using an epoxy with high compression strength.

Where work keyways need repairing a quick metal retaining compound is ideal.

After using a suitable activator, the compound is applied directly into the keyway.

The new key is then pressed in and the assembly restored without having to take apart the pump.

The same product can be used where there is any area where large voids are involved.

(As an aside, the fairly recent innovation of engineering adhesive "sticks" that has been mentioned previously is ideal for maintenance jobs.

The sticks take up little room in a tool box and are small enough to be carried in a pocket.

And being of a semisolid formula, they do not drip).

The harsh environments and operating parameters mean that pump parts are subject to wear, erosion, corrosion and leaks.

The use of adhesive and related products in both assembly and maintenance tasks means that many of the traditional problems can be avoided.

The use of such products at initial assembly means that pumps operate for a great deal longer - and with fewer breakdowns - than had been achieved previously.

Beyond that, where other methods have been used at assembly, experience shows that use of the right adhesive product during maintenance can mean parts that would otherwise be scrapped have been able to be pressed back into service.

Any reputable supplier of engineering adhesive products will be able to provide help and technical assistance and answer specific questions.

Back to top