What makes an anti sink, sink?

[Deanxm]

I understand that the Anti sink sphere seems to be a pressure reserve for the brakes should the anti sink valve close so doesnt have any affect on the sinking of the car, but what would make an anti sink drop around two inches on both axles after a few hours?
Do the anti sink valve(s?) start to leak themselfs?

D

[CitroJim]

Dean,

If this is on your Activa, then a bit of a sink is really pretty normal I find.

I can more-or-less explain why I think it happens but it's a bit complicated and I'm not sure I fully understand why.. It's all to do with the interaction of the rams and gradual pressure loss in them. I'll marshal my thoughts later and try an explanation...

Anti-sink valves rarely leak. Off-times the cause of sinking are flat corner spheres or slightly leaky hydractive electovalves.

[VertVega]

When I asked the same question here, I was told that it might be an internal leak.
In my case it would be front strut(s) letting LHM back to the reservoir

[CitroJim]

When I asked the same question here, I was told that it might be an internal leak.
In my case it would be front strut(s) letting LHM back to the reservoir

That too is a very good and sound cause VertVega. Easily confirmed by measuring how much LHM flows on the leakage returns from the suspension cylinders/struts.

I have seen a pair of front struts with worn/scored pistons that caused the car to sink very rapidly at the front. A good reason to always ensure your gaiters are pulled up...

[Deanxm]

I think i understand, so the anti sink just closes the feed to the height correctors then, so fluid cant flow past the correctors and out of the suspension c?, but of course there is still minimal leakage past the struts and electro valves? which allows it to drop over time.

D

[CitroJim]

Spot-on Dean, the anti-sink valve isolate the height correctors that are terribly leaky, relatively... All that's left that can leak are the struts/clyingders themselves and if Hydractive, the electrovalve.

[Xaccers]

I think i understand, so the anti sink just closes the feed to the height correctors then, so fluid cant flow past the correctors and out of the suspension c?, but of course there is still minimal leakage past the struts and electro valves? which allows it to drop over time.

D

Yes, the pressure in the rear system pushes the anti-sink valve closed, so if the valve is leaky, or the pressure is down due to old spheres or leaking past rams, the valve won't be closed fully, so the back will sink.
Likewise with the front.

I would imagine though, for it to be sinking due to a leaking strut rather than low spheres, then the leak would have to be considerable to sink in that much time, as when fluid escapes, the spheres will "take up the slack" as the gas expands inside them expelling LHM into the sealed system (sealed by the antisink valve).
Once the spheres are empty of LHM, they're not able to exhert any more pressure on the system, so as more LHM leaks, the pressure drops, opening the antisink valve letting the LHM return to the resevoir.

[Deanxm]

Ok i think im with you.
But so far as Activa go a bit of sinking is part of the deal? on high drive or max service setting it doesnt seem to settle but at normal ride height it does.
It doesnt bother me its just if there is an issue i would rather tackle it now, im sure there will be enough issues to sort out once i start driving it.

D

[CitroJim]

A good test of cylinder integrity Dean is to leave it on high and see if it sinks then.

This them counteracts any effect the Activa rams will have on the plot...

On high it should stay up virtually for ever and ever...

[Deanxm]

yes, it does, months at least!.

D

[Sl4yer]

My Activa always sinks at the back from normal height. The only exception to this is when it had the severe leak from the ram hose, when the back stayed up perfectly!

James

[CitroJim]

My Activa always sinks at the back from normal height. The only exception to this is when it had the severe leak from the ram hose, when the back stayed up perfectly!

James

That makes sense James, strangely enough...

[Diabolical]

My Hydractive Estate has been dropping on the back periodicaly for quite a while now, eventually got round to looking at Spheres, rear N/S seems to have a small leak.
I have bought 4 corner Spheres non-hydractive, fancy softer ride like my CX.
One question is will it make any difference with pressure ratio on the other 3

[CitroJim]

Non-hydractive spheres on the rear will certainly give a softer ride, albeit with a small loss of damping. This will be noticeable when well loaded but you can counter this to an extent by placing the suspension in sport mode.

So often on a Hydractive car, the rear corners are found to be ruptured and this will cause sinking. They can rupture without you being aware as the hydractive centre sphere does most of the springing work; the corners more acting as dampers.

[Diabolical]

Non-hydractive spheres on the rear will certainly give a softer ride, albeit with a small loss of damping. This will be noticeable when well loaded but you can counter this to an extent by placing the suspension in sport mode.

So often on a Hydractive car, the rear corners are found to be ruptured and this will cause sinking. They can rupture without you being aware as the hydractive centre sphere does most of the springing work; the corners more acting as dampers.

Jim does that mean if I use a higher pressure centre sphere would counter act the damping on rear spheres.
ie: replace centre sphere with a front accumulator sphere