10 minute Xantia mod....what a difference!

[cc101]

Hi all, I've been doing a fair bit of research on hydraulics lately and the effect air has within a system. Anyway decided to cut the main return plastic pipe that goes to the base of the LHM reservoir, reading the info regarding air in the return fluid due to old pipes and joints being sucked back into the HP pump.



Long story short the ride has improved so much all I've done is drive around looking for pot holes etc! The brakes have improved and there is no more grab and let go symptoms!

I think this must have been the problem all a long on my quest to eliminate the crashy ride!

Chris.

[Mandrake]

Hi Chris,

Very interesting! Give it time though, in my experience this sort of intermittent harsh ride often returns after a period of time...let us know in a week or two whether the ride is still crash free.

I assume you were reading threads like this one ?

http://www.frenchcarforum.co.uk/forum/v ... =3&t=20909" onclick="window.open(this.href);return false;

Somewhere around 6 years ago I posted pictures of my own bodge for this problem on my previous Xantia, I thought it was in the above thread but couldn't find it so it must have been in another thread. As you know the original pipe that you cut has a slot that travels all the way down the side, rather than cutting mine short I clamped a pipe over it that captured the flow and redirected it to the surface as follows:





The idea was for the incoming oil containing unwanted bubbles to be dispersed at the surface of the oil where they could de-aerate easily rather than directing the air bubbles forcibly down into the bottom of the tank right next to the pump inlet.

Yes there are two filters between the return and the pump and the bubbles should travel (slowly!) to the surface, but it seems that if there is sufficient quantity of bubbles coming back in the return line the oil surface tension at the filter is overwhelmed allowing some air to pass through the filters and get sucked into the pump inlet line.

My bodge was relatively successful, the very intermittent harsh ride of that car mostly but not completely went away, and consistently remained improved for years afterwards, the change was big enough that I left it in the car right up until it was sold - the new owner will get a surprise when they go to change the LHM!

If your simpler mod of simply cutting the return pipe short works just as well or better I'm tempted to do it on my current Xantia... please keep us informed of how long lasting the improvement is.

Do you have the measurement of how long you cut the pipe ? And did you deliberately cut it on an angle ? I wonder what the optimal length is, given the average surface level of the oil at normal ride height... is yours above the surface of the oil or just below it ?

PS one other thought, by taking the top of the tank right off and putting it back you might have also inadvertently fixed an air leak on either the pump pickup or main return pipes where they attach at the top...

[cc101]

Hi Simon, I cut it leaving an inch of pipe so it's just above the LHM when set at normal, I also cut it at an angle and put a slit right to the top to prevent the fluid being forced directly downwards. The far right return pipe as you look at the tank from the passenger wing also has a very high amount of fluid being returned under force (believe it's the steering valve return), I took the two long plastic return pipes off to see without the filter being in place. I believe this pipe should be modded too, I'll try and take a video of what's going on and post it.

[taffy]

id put a bit of pipe angled up as far from hp feed as poss....this has opened my eyes too to something i diddn know about and my ride has been a bit harsh at times...will be doing this
well done

[SwissSPEC]

Hmm, anyone tried this on a BX?

[Mandrake]

Depending on the layout of the tank the BX may not suffer from the same problem. From what I can remember (it's been many years!) the GS and CX did not suffer from this problem at all, and had very different shaped tanks with different pipe layouts.

[SwissSPEC]

I thought the xantia tank was exactly the same size/dimensions? Does it have the white flat disc at the bottom where all the crud hides? The picture thats been posted of the tank filters is the exact same thing as the bx one.

[Stewart(oily)]

I thought the xantia tank was exactly the same size/dimensions? Does it have the white flat disc at the bottom where all the crud hides? The picture thats been posted of the tank filters is the exact same thing as the bx one.

The gubbins looks the same but the reservoir is very different in shape, I was looking at a BX one in my garage today.

[Mandrake]

Hi Simon, I cut it leaving an inch of pipe so it's just above the LHM when set at normal, I also cut it at an angle and put a slit right to the top to prevent the fluid being forced directly downwards. The far right return pipe as you look at the tank from the passenger wing also has a very high amount of fluid being returned under force (believe it's the steering valve return), I took the two long plastic return pipes off to see without the filter being in place. I believe this pipe should be modded too, I'll try and take a video of what's going on and post it.

Hi Chris,

Just looking at your picture again, you say you cut the pipe at an angle to prevent the oil being directed straight down, but comparing your picture with mine it looks like the angled cut is at right angles to the wide axis of the filter that it sits within, thus directing the flow straight into the side of the filter element next to the pipe, is that correct ? Did you choose that direction on purpose or was it not something you considered when cutting it ?

I'm wondering if it would be better to cut the angle 90 degrees around from where you cut it to direct the flow across the width of the filter towards the far side of the filter, so that the flow isn't aimed directly into the nearest section of filter ? Or perhaps aiming it down at a shallow angle directly into the side of the filter would minimise turbulence ? I'm not actually sure which would be best.

If you do get a chance to video the oil flow in the tank to see what the turbulence is like that would be very helpful.

Regarding a second pipe with large flow, I was under the impression that the power steering return and pressure regulator overflow returns joined at a junction before reaching the tank and both entered at the same pipe you've modded ? In fact looking at your tank fitting I don't see any of the other returns having a long pipe that needs modifying anyway ?

Another thing for other people to bear in mind is that your car is a sinker with FDV and single pump circuit, I'm not sure without referring to the piping diagrams whether sinkers and non sinkers use the same tank return arrangement, something we need to check.

[cc101]

Hi Simon, I cut it at that angle to stop it being directed into the flow of the other return pipes, on my set up there are 3 plastic pipes which are inside the D shaped filter, 1 large pipe which is the one cut on an angle and 2 smaller diameter plastic pipes which are removable! The far right return which I believe is the steering valve has the smaller diameter pipe which also goes to the bottom of the tank, this is the one that has a very high flow, I've also cut that one. It is still running extremely smooth.

Chris.

[Mandrake]

Still confused Chris, comparing what you say with both your picture and mine

If you look at my picture there is only one long pipe within the D shaped return filter, the one I attached my extension to. There are three smaller return pipes on mine at the top that drain inside the filter but none of them have a visible extension down inside the filter, removable or otherwise - I did not remove any pipes inside the filter for that picture! They are also all press fit low volume return lines.

Bear in mind that mine was a 1997 anti sink model, so it may not be identical.

By the way if the power steering return and pressure regulator returns are separate, its the power steering that will have a greater flow, by a factor of three to one on an anti sink model. I don't know the ratio on a FDV model but it will still be a greater return from the power steering. I believe both flows are merged before the tank on mine though as there is only one high volume return spigot.

I'll try to find the return pipe diagrams in Service Box to see if I can find a difference between the two models and clear up the confusion of which pipe does what.

[isisalar]

I'm following this topic with great interest as I'm getting a hard ride almost certainly caused by air or nitrogen bubbles, hopefully from leaking spheres which will be replaced shortly.
I've had a random thought which may be worth discussion though.
Many years ago I ran a windscreen repairing business and part of the equipment was a vacuum/pressure gauge, trigger operated, I believe they were also used for setting up carburetters. Vacuum was applied to the cylinder holding the liquid resin and this removed all the air in the resin. Bubbles appear on the surface as soon as vacuum is applied and soon vanish into the vacuum. It would be relatively simple to fix one of these to the breather pipe coming off the tank cap after ensuring the cap was sealed and putting the tank under vacuum should remove all gas present in the LHM. Putting the tank under pressure would also show up any air leaks on the gauge.
Keeping the tank under constant vacuum might solve this problem completely but cause problems in the system?
Please discuss chaps.
Cheers
Paul

[Mandrake]

Still confused Chris, comparing what you say with both your picture and mine

If you look at my picture there is only one long pipe within the D shaped return filter, the one I attached my extension to. There are three smaller return pipes on mine at the top that drain inside the filter but none of them have a visible extension down inside the filter, removable or otherwise - I did not remove any pipes inside the filter for that picture! They are also all press fit low volume return lines.

Bear in mind that mine was a 1997 anti sink model, so it may not be identical.

I just want to correct a mistake of mine after looking at a photo of the top of the tank in my previous Xantia - there are in fact 6 return lines that drain into the filter not 4 as I suggested. There is one large diameter one with high flow volume - the one with the long pipe down into the bottom of the tank that has been cut/modified, there are then 3 smaller horizontal spigots which are low flow rate but do have hose clamps on them, finally two vertical push fit pipes which are only leakage returns.

My main point remains though - only the one pipe has an extension down into the tank on my previous Xantia, the other 5 just have spigots at the top without any extension down into the tank, and thus there is nothing to modify on those. I haven't checked my current 1998 Xantia but I would image it is the same too.

[Deanxm]

I have never understood this quest to seperate air from the returning oil, almost any Citroen ive worked on will ride much softer when air is introduced to the system as a result of work being done. Usualy a side affect that rights itself after a dozen miles or so as the system self bleeds. what is the theory that leads some to suspect air could make the ride harsh?

D

[Hell Razor5543]

I don't think a vacuum would work. Some of the LHM is coming back under normal pressure, while some is entering under high pressure. You also have to allow for the level changes (such as when it is in either maintenance position), which is why the tank is under normal pressure, and has a breather pipe coming out of the filler cap. Could the valves handle both pressure on one side and vacuum on the other?

I think Mandrakes' diverter pipe is probably the most effective fix (without a complete re-design of the tank pipework).

Air in the LHM can cause problems such as inconsistency of ride comfort and possible problems in the steering, but worst could be air in the brake lines (which could cause braking problems). The suspension and the steering do self-bleed, but the brakes don't.