Workaround for bubbles in LHM return flow

[CitroJim]

James, not that one but yes, that one Mike! That's the one except mine has blue handles!

http://www.ebay.co.uk/itm/Sealey-Heavy- ... SwPc9W1PPj

It will do all but the smallestt clips and those can be done with a small pair of wire cutters...

Of a number of Xantias I've broken, I've kept as many of the clips as I can for re-use and replacement where Jubilee clips have been used on my own cars in the past...

I did that on Alasdair's car when we replaced the pump and regulator the other week.

[Mandrake]

Regarding the different types of jubilee clips - I always use the thin stainless steel ones and make sure to use one that is no bigger than required - this reduces any "bump" compared to using an oversized clip or using the much thicker stiffer types, which are not suitable for small hoses at all.

The original factory clips are all well and good, but in many applications in hard to reach places its simply too hard to get the access that the special tool requires to re-fit the factory clips. They work well on the assembly production line when half the engine bay is empty, not so good for refitting a pipe that you can barely reach with everything else in place!

Jubilee clips really come into their own here in locations like the plumbers nightmare area on the V6, or the joiner stub on the hydraulic pump feed pipe at the pump end - you can get a screwdriver or small spanner onto the screw in places where you would never fit the handle of the clic tool in.

[lexi]

A better type of fasterer.
http://www.vehicle-wiring-products.eu/p ... pipe-clips

[white exec]

Quite right about Jubilees - stainless, thin and no bigger than necessary - and access considerations. Sometimes necessary on the XM to use a 30cm+ magnetic hex screwdriver. Clip pliers would be impossible. Do produce a sound and tidy joint, though.

[white exec]

A better type of fasterer.
http://www.vehicle-wiring-products.eu/p ... pipe-clips

Yes! Great design. Remember those from the 60s and 70s. And hose end protectors/buffers too, as Citroen OE.
Have bookmarked the site. Thanks, Lexi.

[CitroJim]

A better type of fasterer.
http://www.vehicle-wiring-products.eu/p ... pipe-clips

Yes! Great design. Remember those from the 60s and 70s. And hose end protectors/buffers too, as Citroen OE.
Have bookmarked the site. Thanks, Lexi.

Used those to good effect too.. Even used them in aerial construction

[Mandrake]

A better type of fasterer.
http://www.vehicle-wiring-products.eu/p ... pipe-clips

Yep they are good too.

I use them on any hoses smaller than about 12-15mm. For larger than that I still use Jubilee.

[Mandrake]

Time for an update on this, just so people don't think the ride on my car is completely solved now - it's not. The ride quality is quite intermittent again, however I think I have started to piece together what is happening.

When I was only driving the car a short distance each day the ride remained very good. However when our son was born I ended up doing about 200 miles in just 4 days back and forth to the hospital, comprised of 10 mile trips each way, which were 50/50 30mph residential and 70mph motorway. I started to notice over those few days that the ride got worse and worse until the point where it was getting really quite crashy again. Hmm.

A couple of times while cruising on the motorway and the ride was quite bad I tried partially lifting the car up to above normal height and dropping below normal height while still on the go,(obviously only a couple of inches so as not to be unsafe) in an effort to flush out some bubbles, and that actually made the ride much worse afterwards, not better. Double Hmm, but also maybe a clue.

After our son was back home and the car was hardly used again the ride improved dramatically again over a couple of days. Basically if the car was used a lot especially a lot of stop start driving the ride got worse, but if the car was mostly left to sit, especially if it could sit for a few days between use the ride got much better again, all by itself without any Citrerobics.

I gave this paradox some thought, especially the observation that trying to do a partial Citrerobics whilst on the move made things so much worse rather than better, and realised that one thing we have not considered in relation to air ingress is the pump speed.

It stands to reason that if there is a minor air leak on the pump inlet pipe, and particularly if there is any restriction such as a dirty filter in the LHM tank, that the increased pump speed when the engine is operating at driving RPM (1500-6500) rather than idle (640rpm) could lead to a greatly increased air uptake compared to when the pump is running at idle speed, as the restricted filter would increase the suction through the air leak as the pump ran faster and faster.

Also if part of the issue is turbulence and frothing inside the tank due to the way in which the return flow enters the tank (eg what the 10 minute mod attempts to address) that increased engine RPM means a higher pump flow rate and perhaps worse turbulence inside the filter in the tank when driving than when idling. In other words the problem gets worse at higher RPM.

However normally you would let the suspension lift up at idle and then while driving there wouldn't be a lot of topping up of the suspension done, at least at the front. Any excess bubbles would just circulate from pump to pressure regulator and back to the tank without being drawn in by the suspension, at least right away.

Generally the front suspension would only get a top up if you did something like a parking manoeuvre, where the sharp lock will cause the front suspension to lift up. So a lot of manoeuvring like frequent parking and turning may lead to air entering the front suspension at an increased rate. Meanwhile on the rear suspension it will top up every time that you accelerate hard for more than a few seconds in a row, as it will trigger a height corrector correction. If you don't accelerate hard or only do so in short bursts the rear suspension will tend not to draw in much new fluid either.

Also, if you frequently exit the vehicle after a short trip then enter the vehicle again and make another trip, every time you get in the car some new potentially bubble contaiminated fluid must be admitted into the suspension to lift the car.

Now we start to see a connection - if you drive the car in such a way that the suspension is having to make frequent top ups whilst the engine is at a higher RPM, more air may be drawn in. This would also include driving off in the morning before the car has had time to lift up as opposed to waiting for the car to lift to ride height whilst still at idle. Also if microbubbles are already in the tank from recent driving, every time you get in and out of the car before they have had time to disperse, (which takes hours) more of them go into the suspension.

So waiting for the car to lift before driving, driving with gentle acceleration, not reusing the car multiple times a day, and tending to cruise without any sharp turns such as parking would tend to minimise air bubble uptake and maintain a good ride, whilst driving off without letting it lift first, frequent hard acceleration for more than a few seconds at a time (ahem) and lots of sharp bends and parking manoeuvres could well lead to increased air bubble uptake and a worse overall ride.

Anyone else see any patterns between driving behaviour as above and ride quality ?

I've also found that once the ride is harsh like this that lifting the car right up and down does not help at all - it remains harsh. However lowering the car right down and leaving it for 24 hours then lifting it back to normal height invariably results in a very good ride again. My theory is the same that I suggested earlier in the thread - that we're talking about tiny microbubbles that are not resolved by citrerobics, because they pass through the filters and back into the suspension again. But lower the suspension right down (returning the maximum quantity of oil to the LHM tank) and leave it there for many hours and the microbubbles finally disperse to the air in the tank and thus the majority of bubbles are removed from the entire system.

I think the next think for me to do is replace the bottom o-ring that is leaking on the pump, change the LHM, (which needs doing) perform the 10 minute mod and also clean the filters and see where things go from there.

The pipe joins that I sealed with Silicone are a part of the problem but not the whole problem.

[Hell Razor5543]

Makes sense. However, I personally am loath to make a modification that cannot be undone (such as cutting a pipe short). Would it be possible to fit some form of baffle between those two pipes, so that the LHM has to have circulated a bit in the reservoir before it can get picked up again?

[Mandrake]

A baffle would be better, but having considered this before I can't see any easy way to make one without a lot of work. Cutting the pipe short worked a treat on the previous V6 - I never had any regrets from doing it and the ride remained pretty good right up until it was sold. I might not cut it quite as short this time though.

[CitroJim]

Simon, that's an incredibly interesting piece of research and goes a way perhaps to explaining why a complete change of LHM seems to make such a difference.. I always thought there was a bit of 'placebo effect' at play but now I'm not so sure - your research gives a very good reason for it.

Excellent work... If there as a Nobel Prize on offer for Citroen suspension hydraulics you'd be the winner for sure!

[Mandrake]

Jim I'd just be happy if my car rode nicely all the time! That is reward enough!

Yes, an LHM change is usually accompanied by cleaning the filters, which would tend to minimise bubble intake by reducing vacuum on the pump inlet, especially at higher RPM...

Also doing an LHM change implies disconnecting the pipes at the tank (at least on some models of Xantia) which means that previously leaking hose terminations might be inadvertently fixed.

So the new LHM gets the credit for the ride improvement but it was really (or mostly) cleaning the filters and accidentally fixing air leaks!

Not that changing the oil is a bad idea of course, clearly any muck that is allowed to build up is likely to get stuck in valves such as the hydractive block and cause mayhem.

I've been meaning to change the LHM for a while now (and have not yet on this car) so will of course also clean the filters and I think do the 10 minute mod while I'm there. If the ride is consistently good after that I don't really care exactly what got me there.

[CitroJim]

I'm sure that reward will be yours very soon Simon...

And also new LHM will be generally free of micro-bubbles I'd have thought so you're starting off with not only clean LHM but fully bubble-free too...

[Hell Razor5543]

Although it probably has not yet done the mileage to the point where a Hydraflush is required, it might be worth giving it a go. It could help by cleaning out the pipework, etc..

[CitroJim]

Yes, I'd go along with that James...