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Hydraulic Systems and Cleanliness
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Author Post
gmerry   
Fri Mar 02 2012, 10:16am
Joined: Dec 11 2009
Member No: #21
Location: Scotland
 Hi, does anyone on this forum had any dealings with hydraulic systems and understands the importance of cleanliness.

Anyway, I had to "open up" the LDS system recently to replace two faulty front suspension spheres and this has got me thinking...

Most hydraulic systems have in-service filters with appropriate delta p warnings to let the user know when blocked and/or bypass valves.

Hydraulic systems generate wear particles in use and these need to be kept at low levels if in-service malfunctions are to be avoided.

Any maintenance, even when installing new factory cleaned equipment, will introduce "dirt" particles into a hydraulic system. Do we known the cleanliness level of any new hydraulic fluid introduced into the system (anybody familiar with NAS cleanliness levels). I'm not sure that the LDS we buy brand new would be ultra-filtered and the packaging appropriately pre-cleaned.

Most commercial vehicles have service filters (low micron ratings) for their hydraulic systems including power steering.

So this got me thinking, the C6 has small clearance hydraulic components (front and rear regulator blocks that control suspension rate for example). There does not appear to be any filters in the system other than a coarse strainer in the reservoir filler. Would it be possible or desirable to introduce some filtration into the system. As a kidney loop or use the existing power steering system which continuously circulates fluid. Flowrates? System Pressures, Mounting room for a filter.

Any comments?

Regards
G
drummond   
Fri Mar 02 2012, 12:13pm
Joined: Sep 20 2010
Member No: #238
Location: Aldeburgh
 Very interesting.

I'm not entirely sure that any car has service filters within its power steering. Certainly, RR don't have anything hydraulic that's not Citroen in their (green fluid)rear suspension.

I wonder if the regime for cars (which cover about 120 000 miles/life on average)is different from commercial vehicles, which might cover that in two years? One has to be (almost) aircraft style, whereas the other is, quite literally, fit and forget.

Btw, my LHM system in the DS has a hole in the return fluid cap, to allow the system to breathe fresh air.

Tim
C6Dave   
Fri Mar 02 2012, 12:39pm

Joined: Oct 01 2009
Member No: #1
Location: Northumberland
 G I used to be a fitter for British Coal and we had to change out hydraulic motors in situ on the coal face on £1,000,00+ coal shearers (usually at 03.00, not that it mattered when, as it was always dark anyway )

The pump and motor actually sat in the oil sump so could never avoid coal dust getting into the system with the top of the box removed

The only way to access them on a metre high seam was to blow a hole in the roof, hose everything down as best you could and climb on top with no supports.

Brute force and ignorance were much in force manhandling the old and new motors and at the end of it, the machinery ran

Changing out hydraulic parts in C6 bears no comparison and I'm sure Citroen Engineers thought the system through, allowing for maintenance if required without the end user having to add more filtration
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gmerry   
Fri Mar 02 2012, 02:52pm
Joined: Dec 11 2009
Member No: #21
Location: Scotland
 Good range of perspective there. Actually, the LDS reservoir does have a (small) hole in the cap and I recently pulled one apart (to build a bleeding pressurisation kit as per Citroen manual)and found that there is an internal relief/breather system built into the cap. The later reservoirs have a separate large breather/filter.

I guess the fact that the LDS system is running a pretty standard hydraulic power steering system in combination with quite a specilised or unique suspension system means that any comparison to any other passenger car system may not be that relevant.

Anyway, my two main themes were desirability of filtration and practicality of adding in service practicality.

Personally I don't think the high level argument that if it was needed it would have been added by the Citroen designers stands much close examination. Normal tension between cost accountants, marketing people and after-market maintenance considerations would apply and I could guess who would win those arguments. A good example of this would be the Citroen "stance" that the transmission is lubricated for life.

Regards
G
 

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