davetd wrote:Thanks for the reply Anders. I'll leave it as it is
Why do pre anti sink cars sink at such different rates? Is there a non return valve to the pump or something? My car has an excellent service history and everything including the suspension has been serviced on time since new, so it's not poor maintenance, (which can lead to all sorts of horrors) that I've read about on this forum! I'm just curious
Going down in an hour or so for a non anti-sink model is fairly normal.
The "leaky" components in the hydraulic system that primarily cause the car to sink are the height correctors (which affects sinking at both ends) and the brake control valve. (which affects sinking at the rear only)
Both height correctors and the brake control valve are necessarily somewhat "leaky" due to their design. (In fact the height correctors use no o-ring seals at all, and rely entirely on micrometre machined surfaces)
The anti-sink system adds an additional special low-leakage valve at each end of the car whose sole purpose is to isolate the height correctors from both the suspension and the high pressure supply, and also isolate the brake valve from the rear suspension.
The trigger to cause the valve to go into isolation mode is when the high pressure supply from the regulator drops below the pressure currently in the suspension. (Therefore front and rear anti-sink valves typically cut out at different times)
By doing this the only possible sources of leakage are the anti-sink valves themselves (which have very low leakage) and the suspension struts/cylinders, which also have very low leakage.
As for whether it could be retrofitted, the answer is yes, although it would not be a simple job.
It would require a front and rear anti-sink valve of the right type (hydractive and non-hydractive are different, and front and rear are different) an anti-sink sphere, a bracket to mount the anti-sink sphere on, a hydraulic circuit diagram for both anti-sink and non anti-sink models to compare the differences, and a means of making the necessary custom piping to re-pipe the height corrector etc..
Because most Xantia's already have anti-sink its probably not worth the effort on a Xantia IMHO, although I have considered fitting it to a CX if I ever get one
Regards,
Simon
