C5 hydraulic tank exploded

[white exec]

Many of us could have designed a better modified cap. Not exactly rocket science!

[GiveMeABreak]

Agreed! But I thing the issue is still the rate and pressure at which the fluid can be returned as it is uncontrolled. Something has to give. I recall somebody saying they had the modified cap and they still got an LDS explosion as it couldn't cope - and I don't think any cap would of coped Chris.

[white exec]

You could be right.
To survive that sudden rush-back of fluid "no cap" (plus a bit of splash protection) would certainly cope, and this would have to be the basis for a cap design — something offering almost no resistance . . . which is why I thought of a lightly-sprung ball, or disc, able to lift rapidly off its seat, and open up a large path for air to escape.
YTS stuff, really!

[Hell Razor5543]

I still don't know what was wrong with the previous system (as used on the Xantia and (to a lesser degree) on the BX (both of which I have experience of)).

[white exec]

Marc has explained that the new electric pump needs some positive pressure behind it (forced priming) before it will start to work, after depressurisation etc. Shame the electric pump couldn't have been self-priming - whatever happened to gravity??

[GiveMeABreak]

Yes I have experience of those back to my GS and CX and later days James. Purely mechanical, but have their downsides too as in complete hydraulic failure where a leak or pipe goes, as has happened to me several times.

At least the newer systems are isolated from those same problems, steering, and breaking all separate. Even when Elis was in Europe after suffering a blown fuse so no pump running on his X7, he managed to get home.

[Hell Razor5543]

Yes I have experience of those back to my GS and CX and later days James. Purely mechanical, but have their downsides too as in complete hydraulic failure where a leak or pipe goes, as has happened to me several times.

At least the newer systems are isolated from those same problems, steering, and breaking all separate. Even when Elis was in Europe after suffering a blown fuse so no pump running on his X7, he managed to get home.

I don't want it to break!!!

[GiveMeABreak]

Marc has explained that the new electric pump needs some positive pressure behind it (forced priming) before it will start to work, after depressurisation etc. Shame the electric pump couldn't have been self-priming - whatever happened to gravity??

I think it was James that mentioned that Chris, however I have to disagree on that as well. I’ve depressurise my system several times using Diagbox and have NEVER needed to manually pressurise it.

I think that procedure only applies if you are completely draining the hydraulic system out so that there is literally no fluid in there at all and not generally when you depressurise the system with Diagbox.

[white exec]

Sorry - yes, James.
So, in the normal run of things, the cap could be left loose, or even decently vented? Assume LDS not hygroscopic, like LHM.

[Hell Razor5543]

As I understood it, if there was no fluid in the pump it could not self prime (hence the need to pressurise the reservoir to 0.5BAR (I think it was Paul (citroenxm) who told us this)), but once the pump was fully primed it could run properly with the cap off.

I do agree that the cap is a poor design (and that is the modified one; the first design was bloody useless!!!), and having a simple overpressure safety valve somewhere (cap or top of reservoir) should have been an obvious design requirement.

[xantia_v6]

They could even have designed a cap which disintegrates at 1.5 bar pressure, it would be cheaper and easier to replace than the tank.

I do wonder how quickly you need to drop the car off a hoist to over-pressurise the tank with the modified cap?

[Hell Razor5543]

The modified cap does not let air out, only in. There is a little hole in the cap, and a simple, push fit diaphragm that will seal the hole if there is any pressure in the tank, but will allow air to be drawn in if there is a vacuum.

[GiveMeABreak]

The cap let’s out pressure James, so by definition air.

[Hell Razor5543]

Not on my C5 it doesn't! The cap will let air IN, but not OUT. I don't know about the cap for a facelift or X7, but the simple diaphragm will close the breather hole if there is pressure in the reservoir.

[GiveMeABreak]

James, they are different systems and different tanks and caps for the MK I & II as compared to the X7. This thread started on an X7. You can’t just wade in and start stating things as facts that are not relevant to the model in question,

The X7 tank is materially different as is the suspension system, has a separate venting cap built into the tank, and has a venting pipe. I’m going to leave it there as I’m rapidly loosing the will to live.

The one on the left is from an X7 - note part 3 (tank cap) and & 4 (vent pipe), This changed again later,