Going solo: why less is more in hydraulics maintenance
January 1st 2006

When it comes to cost effective hydraulics maintenance, there's a case for employing the services of a single supplier that can provide both specialist hydraulics engineering support and all necessary products and components, claims WYKO Fluid Power general manager, Paul Lynch.

It is difficult to apply a rule of thumb to whether an item from a hydraulics system (typically; cylinders, valves, pumps, motors or packaged power packs) should be repaired or replaced. The initial deliberation is often dominated by the consideration of 'lead time' versus 'cost of downtime'. The cost pressure that manufacturing industry is subject to today often dictates that in a breakdown situation the fastest solution available becomes the preferred option. Routine maintenance operations have the luxury of allowing more consideration time, but often result in the same decision being made simply because of the nature of the components.

When to replace

Availability is the key; the smaller an item is, the more common and the less costly it is, the more likely it is to be found on the shelf - in this instance, when an item is available off-the-shelf, a replacement is usually the preferred choice. Larger items that individually can cost thousands of pounds each are more likely to be stocked in component form, or as is the case with large cylinders, cylinder-rods and bodies are kept as semi-finished stock that can be machined to suit at short notice. New items tend to be manufactured to order and are subject to standard lead times of many weeks.

The larger or more specialist a piece of equipment is, the less likely it is to be held in stock as a complete item, large cylinders and pumps are generally repaired and it is rare that a completely new unit is used, regardless of the situation. In routine maintenance situations where a complete system is due for attention, the cleaning and remanufacture of parts is still only carried out when the cost of a new replacement system far outstrips that of a refurbishment. The cutoff point does change marginally in a full system refurbishment; individual items with a replacement value of less than £500 will generally be replaced automatically and after that point a repair is always a possibility.

The market dictates

The consolidation of manufacturing supply that has happened in the pneumatics sector is yet to reach the hydraulics market to the same extent and there are still a large number of hydraulics component manufacturers out there. Many component manufacturers however, tend to concentrate on direct supply to large OEM customers - leaving engineers in the general industrial market with no choice but to source replacement components and repair services from third party suppliers.

This situation is no bad thing for the end user when he has access to a distribution company that holds a broad range of stock and also offers expert engineering support. Advice on a repair or replace decision can be wholly dependent on the type of supplier who is contacted, i.e. a repairer or a new product distributor is likely to err on the side of offering or advising on what they are best able to supply. A balanced opinion on the other hand, can only be provided by a supplier that specialises in both.

As a result, the Maintenance Repair and Overhaul (MRO) sector of the market has moved positively towards those suppliers who can offer a balanced approach. Such companies have fostered the increasingly hard to find skills required to accurately specify replacements and analyse problems, return hydraulic equipment back to the original manufacturer's specifications and re-commission items such as pumps, valves and actuators.

Repairers also have to invest in extensive spare part stocks and offer flexible around the clock services to meet customer demands.

Throughout our remaining heavy manufacturing industry there is still a large installed base of larger capacity hydraulics systems that are no longer manufactured or are too costly to replace and require increasing levels of maintenance support.

It is common to find aged and often obsolete components in critical systems and processes; commonly these include sheet metal presses, steel rolling mills and machine tools such as broaching machines. In many instances, the Original Equipment Manufacturer is no longer trading.

Due to the high cost and relatively low volume manufacture of this equipment, when a direct replacement is available it can often mean long lead-times for nonstock items. Deliveries for units such as larger piston pumps are typically in the region of 30 weeks. A repair is usually the most cost and time effective solution.

Many existing manufactures do offer spares support programmes and specialist repair services for obsolete equipment, but it is rare that a component unit fails in isolation, requiring a more extensive service than is often available from a single manufacturer.

When to repair

Repairs to pumps, motors, cylinders and valves are possible even after catastrophic failure, with reverse engineering and complete rebuilds being both economic and possible in order to return them to satisfactory condition. For example, repairing large variable displacement piston pumps is usually the economic solution to get operations up and running again. Even after analysis shows that the casing is the only salvageable component, porting plates and pistons can be replaced or remanufactured and the unit recommissioned in a matter of days; whilst new units may cost in the region of £40,000 and be subject to 30 week lead times, a repair can cost a fraction of that figure and be completed in a matter of days. This type of unit is usually found in critical applications, also making downtime costs a significant factor in the final decision with some units being repaired many times over before they are entirely replaced.

Large hydraulic cylinders can also be effectively repaired using reverse engineering where necessary to manufacture and replace badly worn or damaged bores and rods. Stocks of standard ground rod and honed tube are machined to meet the full specification of the cylinder whilst any undamaged items such as caps, piston heads, etc. can be salvaged. Cylinders are then rebuilt and fully tested to maximum pressure ratings before delivery.

When repairing hydraulic pumps and motors where full performance and reliability are to be reinstated, only limited reworking is recommended. This does not negate the need for emergency repairs to minor damage such as re-machining worn pistons, cylinder blocks and valve plates for smoother running. These options are only really viable when engineers need to get systems up and running as soon as possible or when obsolete equipment needs to be remanufactured, however the limitations of reduced life and dependability should also be understood.

Testing times

With optimum performance derived directly from dimensional clearances between forced parts of typically 0.5 to 40 micron, it is essential only the highest quality replacements or original spare parts are fitted exactly in accordance with the manufacturer's recommendations.

Although exact application parameters cannot always be replicated, every repair must be 100% tested to ensure performance has been achieved, requiring complex facilities and expert knowledge to accurately verify pressure rating and full range volumetric efficiency. Full hydraulic testing facilities for large components are also expensive and so the choice of supplier is not simply important in order to meet deadlines, but to ensure every item is fully pressure and performance tested before it is delivered to site, no matter how large it is.

Whether a new system is being installed, or an item is being repaired or remanufactured, it is difficult to emphasise enough the importance of quality assured components and rigorous testing. The high pressures and high loads typical of hydraulic systems mean that safety is of paramount importance as even the smallest mistake can lead to catastrophic failure. Only a supplier that will guarantee the quality of a component, a kit or a complete system should be trusted to deliver on this type of equipment.

Whether it is a hydraulic component or a complete system, a good maintenance supplier should be able to provide all the information needed to make an informed choice on whether to repair or replace.

Where practical, an individual item can be collected from site and returned to a workshop for assessment, a larger item can be inspected on site and a balanced view on the options provided all within 24 hours. A full system assessment can take longer based on its size and complexity and there are many continuous maintenance services on offer from regular oil analysis to noise and vibration testing to ensure emergencies are avoided whenever possible, all are available from WYKO.

More articles from ERIKS UK: