anti sink sphere problems...

pugxpert · Post by **pugxpert** » 14 Dec 2005, 16:15

the main accumalator situated on pressure regulator does the front brakes and holds a resevre of pressure ,it has to be there by law to meet type approval regulations and the centre rear does rear brakes,you can buy anti sink valves or spheres sepreratly through parts.in answer to the question if your suspension is dropping that quickly it could be another problem may be with a rear cylinder.

TooMany2cvs · Post by **TooMany2cvs** » 14 Dec 2005, 16:35

jeremy wrote:I'm getting confused here - anti-sink sphere same as a main sphere? What is a main sphere?

I take "main sphere" to be the accumulator.

Pugexpert is quite right - anti sink function is dependant on the VALVE not the sphere. A/S cars have a relatively weak pump for the brakes and suspension and pressure drops in the system after the A/S valve as normal.

True - the 6+2 dual-circuit pump on later XMs and Xants is lousy compared to the earlier single-circuit ones, but the steering is separated off, so in the event of a lack of pressure from the pump, you don't have the thirsty steering sapping the reserve. You will still lose suspension before brakes - and, yes, that does take the rear brakes with the suspension - but they never do anything anyway. How many of us have had to free stuck rear pads over the years?

When starting you get the situation of the A/S valve opening but there being insufficient high pressure LHM to sustain the suspension and power the rear brakes - so back can drop and there be no brakes. A/S sphere should discharge then and provide pressure.

But at that stage, the STOP light is still on - and the fact there's no (rear) brakes shouldn't make any difference anyway, as you don't drive off before the red lights go out, do you?

Mandrake · Post by **Mandrake** » 14 Dec 2005, 19:35

Come on people, stop being silly here

The anti-sink sphere has been covered many times before, and it is a dual purpose sphere. A better name for it would have been "rear brake accumulator which also slows down rear sinking" but it would have been too much of a mouthful

It's primary purpose is as a rear brake accumulator, and the reason it is needed is simple - in older Cit's if the main pump and front accumulator both failed you had no front brakes, but you still have rear brakes running from rear suspension pressure for an (admitedly slow) emergency stop.

With the introduction of anti-sink valves, were it not for the anti-sink sphere, if the pump and accumulator sphere both failed you would have NO brakes at all, because the loss of main pressure will shut the rear anti-sink valve and isolate the suspension from the brakes. NOT GOOD.

So the anti-sink sphere is there to supply the rear brakes if the main system pressure dissapears, and is therefore a safety feature.

However it ALSO plays a role in minimizing the sinking rate of the rear, because it helps to keep the rear anti-sink valve firmly CLOSED once it initially closes during sinking. With a flat anti-sink sphere, the leakage of pressure from the anti-sink sphere circuit through the brake doseur valve will cause the anti-sink valve to periodically OPEN momentarily to equalize the pressure change and each time this happens the rear suspension will go down a little bit - result is accelerated sinking.

This would be most apparent when the main accumulator is GOOD and the anti-sink sphere is BAD, and the brake doseur valve has higher than average leakage. (Eg old age)

And to the chap that said the anti-sink sphere can affect the ride slightly - yes I believe it could, after all it is a 50 bar sphere piped indirectly to the rear suspension, however because it is connected through long skinny pipes it only has minimal effect due to flow rate restrictions...(luckily, as it has no damping valve in it...)

Regards,
Simon

erez · Post by **erez** » 14 Dec 2005, 19:51

so you're saying that i should replace the anti sink valve?
as i said, the rear "drops" down 20 seconds after engine shut off.
it drops fast (fast enough that if you were under the car you would not be under any car - anymore)
i understood the purpose of the sphere, both the accumulator and the anti sink spheres are new. and the rear suspention spheres are also new.

Erez.

AndersDK · Post by **AndersDK** » 15 Dec 2005, 00:34

Thanks to Simon for a very precise and informative explanation on the rear antisink sphere.

Erez :

Its known for the antisink valves to leak and then the car drops fast - despite the "antisink" feature.
Instead of fiddling in the dark and fork out too much money I'd make sure it's not some other problem that makes your car sink too fast. The only other option is one of the rear suspension cylinders.
If they leak back (not out on the road - but internally) it will be seen in the plastic lines from the rubber bellows. And it would be the rearmost of the 2 plastic lines on each suspension cylinder the leakback is found.

Its fast & easy to check.