How clean hydraulics is the key to reliable hydraulics.

Cleanliness is key to reliable hydraulics. Yes, you may get failures for assorted engineering reasons, but our take is that building systems clean dramatically improves reliability and that then flushing a system can be an amazingly good investment.

Keep in mind the difference between building clean and flushing to clean a system. Yes, flushing may be a great call, but like the old beer advert, “it won’t reach the parts”. For us, “clean” is vital.

Why are we always battling filth? Where contamination comes from is a long story. In principal, air is laden with all manner of filth whether metallic, non metallic or organic. Open a loading door and filth blows in. Use an air line and dirt is blown around, moving it from where it was previously lodged. If a clean area uses empty white benches and open light coloured floors that can be washed clean before starting a job, how many assembly shops can say that they operate this regime? If you have “stuff” on your benches and floors, then you will be fighting filth. Just leave a clean room wipe on a bench for a few hours then look at it with a watchmaker’s eyeglass. You will be shocked. When parts are stored, they will inevitably become dirty and need cleaning. You have just simply got to be assembling clean parts. You could read and write volumes on what clean means, but even washing in virgin solvent and not seeing any visible contamination washed off is a good start.

When parts are assembled, screwing threads together or sliding parts home will generate some sort of contamination which is where flushing is invaluable.Unless operatives robe up, no end of muck falls off people. Wearing clean room overalls such as Du Pont “Tyvek” material can be a good start.

Where do you start in addressing this?

Basic house keeping for cleanliness needs tweaking. Food is a total no no in an assembly area. Cardboard has to be banned as it is a terrible source of quite destructive fibres. Paper towel needs to be banned and replaced with lint free clean room wipes. Woolly jumpers are an unmitigated disaster. People should be wearing clean laundered overalls and preferably disposables. Air guns are pretty bad news.

Much as flushing has a dramatic effect, I think improving assembly cleanliness has to be a first step. You need to make sure that contamination is not stuck on seals and in grooves. This will never be flushed clean by its nature, as flow will never reach the areas.

Many hydraulic systems seem to get by being assembled in a “shop” but are effectively designed to be self flushing. If the flow generated by the pump passes through a high pressure hydraulic filter then any oil returned back to tank passes through a low pressure return filter, you are going a long way to running a clean system. Filtration like this will not help if there is already contamination within a component, as the damage may be done to that or other parts before the filth is eventually caught. Never the less, there is flushing in operation of the system. Assembling clean has still got to be a big thing.

If the system does not have any filtration and maybe only has a strainer (for example as a 150 micron strainer rather than a 3 micron filter), you really are risking reliability unless the kit has been built clean.

Flushing after assembly is a good call. Clean, filtered fluid is fed into the system or component and then back to tank through another filter. You are relying on a turbulent enough flow though a system to flush out muck until it is much cleaner. One proviso is that you won’t be flushing and cleaning any legs where the flow does not go. Hence the need to look at the system and maybe operate valves to flush the whole lot. The system is flushed with many times its volume and lo and behold, it becomes cleaner. You also need some means of measuring the cleanliness to decide whether flushing is effective. Leaving it running “for ages” is a bit hit and miss. I rate Filtertechnik on  http://www.filtertechnik.co.uk. They offer an analysis service for oil samples or an on line instrument. MP Filtri amongst others also does instruments, both on line and for analysing a sample off line on your site. At Sarum Hydraulics we use both “send away” sample and on line monitoring, but keep in mind that the on line kit needs calibrating. There again, you have an immediate result rather than waiting for a few days for the analysis to be e-mailed back. Sending a sample away will also measure water and other contaminants or whatever you ask for.

There is lots of stuff on the web on cleanliness standards.

If you are a hydraulic manufacturer, then cleanliness is an issue for you, not just for “aircraft people”.

Have a look at our products on www.sarum-hydraulics.co.uk .