C5 hydraulic tank exploded

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Re: C5 hydraulic tank exploded

Post by Mandrake »

Surely this is a major design flaw if the reservoir can explode due to innocently jacking up the car without setting the suspension to maximum ?

No prior Citroen's suffered from this problem. Makes me glad I don't have a C5... :roll:
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Re: C5 hydraulic tank exploded

Post by GiveMeABreak »

A completely different system on the X7, even from the MK I & MK II C5s. There are no front strut return pipes on the X7 like on the earlier models, fluid is returned via the front rigidity accumulator. So a lot of fluid under intense pressure potentially being forced back through this unit to the tank under the weight of the car if dropped down uncontrolled.

Even the modified vented LDS cap released as a replacement part, is insufficient to allow this amount of pressure to be released. A completely backward approach, agreed.
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Re: C5 hydraulic tank exploded

Post by Paul-R »

When I had four new tyres fitted a couple of months ago I just loosened the cap myself and tightened it up afterwards. Saves a lot of hassle if things go wrong.
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Re: C5 hydraulic tank exploded

Post by crapday69 »

GiveMeABreak wrote: 13 Mar 2019, 19:23 A completely different system on the X7, even from the MK I & MK II C5s.


Apart from the aforementioned problems, is this a better system than the old.
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Re: C5 hydraulic tank exploded

Post by GiveMeABreak »

Well, to be honest, I believe not.

The newer X7 struts, as 8 mentioned earlier, not only have no leak back pipes on the struts, but the struts themselves are bonded rubber to metal. So any weeping or fluid is going to come from the top of the bonded boot, requiring the whole strut to be replaced.

On the earlier MK I & II C5s, the strut has a significant number of replacement parts seals and the like that can be replaced. With these newer ones there are NO spare parts, the whole thing has to be replaced.

I’ve never had a strut replaced ever, until the X7 where I recently had to have a front one replaced at a cost of £400 (that’s getting the strut cheaper from Poland) and fitting at main dealer.

Having said all that, the newer system has an additional sphere ( 2 rigidity spheres at the rear, 1 at the front, so 7 in all) over the 6 spheres on Hydractive 3+ on earlier systems. But with 4 spheres at the rear, you still need a bit of weight in the rear to get a really damped ride at the rear as you are riding on 4spheres in non-sport mode.
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Re: C5 hydraulic tank exploded

Post by crapday69 »

I had to get a front strut replaced on my Xantia years ago. Tony over at Citroen services (now Cam Autos) in Rutherglen, Glasgow. He took a good one from a scrap Xantia, but after doing mine, he said he will never try that agin and just quote with new ones. I take it, it must have been a b++***d to get off without damaging it.

Anyone used Cam Autos incorporating Citroen services. I always found him very reasonable. A lot cheaper than a main dealer but a little more expensive than a local garage, but with years of Citroen experience I think its well worth it.
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Re: C5 hydraulic tank exploded

Post by MikeT »

GiveMeABreak wrote: 13 Mar 2019, 19:23 A completely different system on the X7, even from the MK I & MK II C5s. There are no front strut return pipes on the X7 like on the earlier models, fluid is returned via the front rigidity accumulator. So a lot of fluid under intense pressure potentially being forced back through this unit to the tank under the weight of the car if dropped down uncontrolled.

Even the modified vented LDS cap released as a replacement part, is insufficient to allow this amount of pressure to be released. A completely backward approach, agreed.
I'm obviously missing vital bits of information re this unwanted reservoir compression phenomenon - is it limited to struts without leak-off pipes (which my car does have) or does it just mean there's further risk to other components (ie front rigidity accumlator)?
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Re: C5 hydraulic tank exploded

Post by Hell Razor5543 »

The cause of this problem is very simple. The LDS pump is incapable of priming itself. This means that (when it is first set up, and (later) when the system is de-pressurised) it has to be under pressure for the pump to get the LDS fluid moving around. The only way to do this is to pump a little air into the reservoir (about 0.5BAR) to get the pump working, and then it will work (even with the reservoir cap loosened).

The LHM system was far better, as it was not a pressurised system (in fact there was a breather pipe to allow for the changes of LHM fluid in the reservoir), so there was a far lower chance of the reservoir failing under load.
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Re: C5 hydraulic tank exploded

Post by white exec »

Given that the pump needs this priming pressure (what a crass arrangement), surely to goodness it would have been possible to design a pressure cap that would permit the necessary 0.5bar pressurisation, but would allow a large and sudden volume of air to promptly escape, if the car was dropped back on to its wheels. Quite simple stuff, I would have thought . . . like a light spring on a diaphragm or plastic ball.
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Re: C5 hydraulic tank exploded

Post by Hell Razor5543 »

The cap has a very simple design. There is just a diaphragm in the top, that will let air in but not out.
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Re: C5 hydraulic tank exploded

Post by GiveMeABreak »

MikeT wrote: 14 Mar 2019, 11:52
GiveMeABreak wrote: 13 Mar 2019, 19:23 A completely different system on the X7, even from the MK I & MK II C5s. There are no front strut return pipes on the X7 like on the earlier models, fluid is returned via the front rigidity accumulator. So a lot of fluid under intense pressure potentially being forced back through this unit to the tank under the weight of the car if dropped down uncontrolled.

Even the modified vented LDS cap released as a replacement part, is insufficient to allow this amount of pressure to be released. A completely backward approach, agreed.
I'm obviously missing vital bits of information re this unwanted reservoir compression phenomenon - is it limited to struts without leak-off pipes (which my car does have) or does it just mean there's further risk to other components (ie front rigidity accumlator)?
This has nothing to do with the initial pressurisation / priming of the tank James. Mike is asking about the LDS tank explosion phenomenon (correct me if I'm wrong Mike).

The problem on the X7 Hydractive 3+ system and the tank issue is thus: (and I'm not including all the other technical interactions that happen).

Assume car is set on NORMAL driving position.
As the car would normally travel on the road, the strut pistons move according to the amount of pressure in the cylinder. As the car rises and falls normally, fluid is drawn from the LDS tank, and expelled as the car rises and falls over dips and bumps.

Now when the car is raised to the mid high or high positions using the electronic control, the LDS return to the integrated hydraulic block reservoir is blocked by the exhaust electrovalves. So on normal suspension, the exhaust electrovalves will be locked to the normal height setting. So if you raise the car on a post , wheels hanging, fluid is drawn into the system as it would if if you went over a hump in the road as the car lifts off - or in this case under the weight of the wheels pulling the pistons down. The weight of the wheels pull the pistons to their maximum travel.

So as the exhaust electrovalves are not set to keep the car at maximum height, when the car is often lowered back to the ground (very quickly in some cases), the pistons are forced back very quickly and all that excess LDS fluid is forced back under pressure of the car weight, back through the valves and into the tank.

If you were instead, to raise the car to high position first, then the exhaust valves would be locked into position at the highest height setting thus preventing all that fluid returning back to the tank, maintaining the car at the highest height level. So this would allow a controlled return to normal position when the manual control is set back to Normal.
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Re: C5 hydraulic tank exploded

Post by Hell Razor5543 »

My post was to explain that, if Citroen had not used a system that needed the pump to be primed for it to work, the reservoir would be able to 'breathe' and so a rapid change in fluid levels/pressures would not result in the reservoir splitting.
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Re: C5 hydraulic tank exploded

Post by GiveMeABreak »

If the LDS tank was airtight it would not allow fluid to flow from and then back to the tank.

It is completely different in that this system does not require the pump to be constantly operating - it can quite happily maintain the pressure and fluid in the system until it needs to make a large compensation or correction. The extensive use of intake and exhaust electrovalves maintain and control the pressure very efficiently - the issue arises when the system cannot take account of an intervention (not so much in being lifted off the ground), but when being returned under extreme pressure when it cannot control the return of the fluid.

Consider also that when the car is on a lift, it is highly likely the BSI will have gone to sleep after a few minutes as the doors will be shut. So that also means the suspension ECU is asleep and the E Valves set at the last known height setting. They cannot adjust if the system is asleep.

Is it ideal? Probably not for Joe Public after a lack of communication - but Citroen wanted to simplify the system as 'worry free', 'reliable', 'maintenance free' to sell it. But now we are aware we can take preventative measures. Not that it will be a worry for Citroen any more of course.....
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Re: C5 hydraulic tank exploded

Post by Hell Razor5543 »

The problem is that the reservoir can 'breathe' in, but (due to the simple valve in the cap) it cannot 'breathe' out again. I never said it was airtight, and I did say that (once the pump had been primed) the LDS system would work with the cap loosened.
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Re: C5 hydraulic tank exploded

Post by GiveMeABreak »

Sorry, but that is the reason why there was a modified cap containing a valve James - to allow excess pressure to escape. The problem is, that in the case of rapid and extreme pressurised fluid return, the valve is insufficient to cope, so causes the tank to explode.
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