accumalator sphere

lurchy666 · Post by **lurchy666** » 23 Oct 2009, 11:12

ok i've got a 1.9 td xantia on a p plate, i've done some digging around on here cause i got problems and found what i think to be my problem but thought i'd ask any way,

right the problems
1. on first start up (or after car has been sitting for more than 30 mins) the rear end drops from normal riding hight to the floor then takes about 30 seconds to rise to normal again
2. the acc sphere clicks every 11-12 seconds when on normal riding hight
3 the brakes are very on or off
4 if u drop the suspension to the deck and then try to put it to full (i.e. when doing citarobics which i do at least once a week) the pressure light comes on and flickers and takes about 30 secs to go out

now i'm thinking its the accumator sphere what do u guys think,

Sid_the_Squid · Post by **Sid_the_Squid** » 23 Oct 2009, 11:42

I would say points 1,2 would be indicative of a flat or near flat accumulator sphere.
Don't know about 3 or 4 though.

lurchy666 · Post by **lurchy666** » 23 Oct 2009, 12:03

well i thought 3 might be if it has dumped what ever gas it in the sphere into the braking system

Post by **RichardW** » 23 Oct 2009, 12:32

1 could well be a flat anti-sinksphere at the back, but with an 11s tick, the accumulator needs doing first. The light coming on when going from low to high could also be related to the flat accumulator, but cleaning the LHM filters might help, but it could just be the pump's a bit tired. On/off brakes is 'normal' for a Xantia - especially if someone has modified the brake pedal and removed the spring. Gas in the brakes usually manifests itself as press the pedal, and get a delay before anything happens, and during the delay you usually press harder so that when braking happens it is pretty sudden!

Sid_the_Squid · Post by **Sid_the_Squid** » 23 Oct 2009, 12:46

Stop light coming on when going from the lowest position is perfectly normal, taking about 30 seconds probably nothing to worry about, slow pump mostly likely, not sure about the flickering though.

lurchy666 · Post by **lurchy666** » 23 Oct 2009, 12:55

well i'll get accumator sphere done i did find one on gsf (i think it was there for 29 quid with p+p) unless any one knows anywhere better, i have read how to do it on various posts just one question tho what is the best way to get the sphere off cause i've read 2 ways to do it either chissle and hammer or a sphere tool, and if sphere tool where is the best place to buy one as i've seen a couple on ebay

also number 1 only happens when turning the engine to start and when started (ie it dont sink when left only when u start it)

Sid_the_Squid · Post by **Sid_the_Squid** » 23 Oct 2009, 13:06

N45304 ACCUMULATOR SPHERE XANTIA ACCUMULATOR 20.90 +Vat

Thats from GSF , that will be an amtex one, IMO just as good as genuine Citroen ones, I know some people will only use genuine Citroen spheres, fair enough; I'm perfectly satisfied with the quality of the amtex ones.

Sphere tool wise, I personally use a chain wrench, its not one of those little oil filter one though, quite a beefy one, looks like a combination of a chain wrench and mole grips, purchased from my local car parts store.

Car sinks when started as there appears to be enough pressure so the anti sink valves are disengaged, but there is insufficient pressure built up in the system to keep the car suspended, because there is no 'accumulated' reserve pressure in the accumulator sphere, so car sinks, if there accumulator sphere was good, the car would not sink as it would be able to provide additional required pressure. Well thats my theory.

Old-Guy · Post by **Old-Guy** » 23 Oct 2009, 13:16

The reason why the car only sinks to the floor when on starting is because the rear anti-sink valve is doing its job of sealing off the rear hydraulic circuit. When you start up, the pump provides enough pressure to open the valve allowing the pressure at the rear to partly re-pressurise the whole system. My diagnosis is that the (front) accumulator sphere is completely shot. As it also acts as a damper to smooth out shock waves in the hydraulic circuit, it needs changing as a matter of urgency before the pump is damaged (any further).

It also sounds as though the rear (anti-sink) accumulator is fairly tired too.

I think what you describe as "On-Off' brakes is probably gas in the brakes lines (dead-ends that don't get purged by Citarobics). You'll have to thoroughly bleed the whole system when you change the accumulator(s).

Get GSF to give you the part numbers for the correct spheres for your car - they are very helpful and knowledgable.

It is normal for the STOP light to stay on when starting up, but only for 10-15 seconds; any longer indicates that the accumulators aren't working properly - either (getting) flat or a leak somewhere.

Sid_the_Squid · Post by **Sid_the_Squid** » 23 Oct 2009, 13:22

Hey Old-Guy, I'm sure I read a thread on here somewhere, that despite the name the rear 'anti-sink' sphere is in fact related to the rear breaking system, not contributing in anyway to the anti-sink circuit.

lurchy666 · Post by **lurchy666** » 23 Oct 2009, 13:34

old-guy is that the same old guy as in this page http://www.attfield.dircon.co.uk/xantia

cause that's where i got most my information from about accumator spheres etc and a very usefull table on spheres, cheers for such a useful page if that is you

i'll get it changed as soon as poss and bleed the brakes afterwards as well as described on the page above, cheers

Sid_the_Squid · Post by **Sid_the_Squid** » 23 Oct 2009, 13:39

I believe they are one in the same person, yes the sphere table is very useful, especially if you fancy a softer or harder right

Citroenmad · Post by **Citroenmad** » 23 Oct 2009, 14:37

Sid_the_Squid wrote:Hey Old-Guy, I'm sure I read a thread on here somewhere, that despite the name the rear 'anti-sink' sphere is in fact related to the rear breaking system, not contributing in anyway to the anti-sink circuit.

No thats not 100% true but I have read that on here myself too.

The anti-sink, as its name suggests, is for the anti-sink. It operates the anti-sink valve.

Im not sure in what way the anti sink is related to the rear brakes. 'sinking' cars still have brakes?

In fact cars with anti-sink dont have brakes once the car is turned off. However sinking cars (non anti-sink) do have working brakes for a short time, until the pressure is lost.

Though saying that i might be totally wrong, though i think thats about right?

Id like someone to fully explain its use, as there seems to be so many contridicting views on here as to its actual main purpose its very difficult who to believe at times. Its certainly confusing.

deian · Post by **deian** » 23 Oct 2009, 15:12

Hi lurchy,

1. is related to the rear anti sink sphere, it's there to keep the back from sinking, and if the main accumulator sphere is duff too, then the pump works hard at start up to pressurise the whole system

2. 11-12 seconds is not ideal, if your aux belt snaps then you have no brakes or steering, better get a new one

3. brakes on off does mean the air has worked it's way down the brake lines (which do no bleed as they are a dead end, the suspension steering all pump round and back into the lhm resevoir, when you put new spheres on, be sure to bleed the brakes, it's a one person job, my 9yr girl old could do it!

4 if you drop it down, then the circulatory fluid (i.e not down the brake lines) will mostly go from the piston struts to the lhm resevoir, the spheres will all be pushing their nitrogen air into negative pressure so they are full depressurised too, if you look into your lhm resevoir after a minute of two when car has been flat (engine still running), you will see tiny bubbles (or big ones ur if unlucky) or nitrogen which has leaked from the duff sphere (accumulator or suspension) into the lhm fluid and you will get a crashy ride (the lhm cushions the air bubbles first then the spheres). If you have a really bad accumulator sphere you will see the pulsing of the main accumulator regulator clicking into the system, you will see a small tsunami in the lhm resevoir if you flash a torch in it.

The accumulator sphere also smoothes out spikes in the hydraulic system so you will theoretically enjoy a nicer ride once it's done.

the anti-sink sphere IS an rear anti sink sphere (citroen implemented it to make the xantia a more normal looking car to attract more buyers, this in turn allowed them to make a less powerful pump, less powerful pump means more efficienct engine etc etc), but it is supposed to stop it sinking overnight and also as a backup for the rear brakes when there is more weight in the back, think of it as taking the pressure off the main accumulator sphere in emergencies and on morning start ups

as for the flickering light, it happens all the time, even on mine, it will take time to re-pressurise with a duff accum.sphere, and when the transition from what the pressure switch thinks is a dangerous pressure (i,e the stop light) to a safe one safe for braking/driving etc, there is a point in between when it makes that transition hence the flickering, nothing to worry about.

also i will remind you that if you car is low on coolant it will tell you to stop too, it's not always related to the hydraulic system, but when it does say stop better stop just in case it is a hydraulic fault.

hope that helps clarify things, mandrake (simon) is the man in the know on hydraulics, he may pop by if this thread lures him.

Citroenmad · Post by **Citroenmad** » 23 Oct 2009, 15:23

deian wrote:
the anti-sink sphere IS an rear anti sink sphere (citroen implemented it to make the xantia a more normal looking car to attract more buyers, this in turn allowed them to make a less powerful pump, less powerful pump means more efficienct engine etc etc), but it is supposed to stop it sinking overnight and also as a backup for the rear brakes when there is more weight in the back, think of it as taking the pressure off the main accumulator sphere in emergencies and on morning start ups

That certainly clears that up, thanks for that.

Pretty much as i thought though was unaware its used when there is more weight in the back.

I couldnt understand people saying its nothing to do with the anti sink function!?

Interesting reason why Citroen desiced to fit anti-sink

Post by **RichardW** » 23 Oct 2009, 17:46

Citroenmad wrote:
deian wrote:
the anti-sink sphere IS an rear anti sink sphere (citroen implemented it to make the xantia a more normal looking car to attract more buyers, this in turn allowed them to make a less powerful pump, less powerful pump means more efficienct engine etc etc), but it is supposed to stop it sinking overnight and also as a backup for the rear brakes when there is more weight in the back, think of it as taking the pressure off the main accumulator sphere in emergencies and on morning start ups

That certainly clears that up, thanks for that. Pretty much as i thought though was unaware its used when there is more weight in the back.

I couldnt understand people saying its nothing to do with the anti sink function!?

Interesting reason why Citroen desiced to fit anti-sink

Er, no, not right....

Consider this - the front and rear suspension systems are hydraulically very similar (HP feed, height corrector, suspension struts) - and yet in anti-sink cars, the front does not need an anti-sink sphere, prevention of sinking is taken care of by the antisink valve. The sphere's function must therefore be more than stopping it sinking per se! This function is in fact taken up by the anti sink valve which sits between the height corrector and the struts, and 'monitors' the HP supply pressure. If the HP supply pressure falls below the suspension pressure in the struts, then the valve closes and isolates the struts from the rest of the system, and as the struts have relatively low leakage, the car stays up. So why only a REAR anti sink sphere? Well, there is one crucial difference between the front and rear of the car- the rear brakes are fed off the rear suspension, whereas the front brakes are fed off the main HP circuit (a beautifully simple piece of design that ensure that the rear brakes always have the correct pressure for the load being carried!). This is where the rear anti-sink sphere steps in (you can see where this is going.....!) the brake valve is notoriously leaky - witness older cars without anti sink where the rear is on the floor pretty soon after switch off, but the front can stay up for several hours, whereas you might expect the extra weight of the engine to collapse the front suspension first. The reason for this is the brake valve - it can leak off the pressure in the rear suspension pretty fast. In anti-sink cars this would have 2 effects:
1 it might cause instability in the rear antisink valve causing it to open when it should be closed, and
2 once the valve is closed the rear brakes are isolated from the main reservoir of system pressure (the accumulator) and hence there is no rear braking effort.

So, the anti sink sphere performs 2 functions:
1. it keeps the anti sink valve shut once it has closed, and
2. it provides a reservoir of pressure for the rear braking circuit in the event of a loss of system pressure (note that the front brakes are provided from the main accumulator, since the security valve closes and isolates the main suspension circuit from the brakes if the system pressure falls).
I suspect that Citroen may have HAD to provide the sphere for reason 2, as otherwise only the front brakes would have a reserve of pressure.

So, why does the car sink straight after start up? Well, this is in fact a sign that the rear struts and antisink valve are in good condition! The valve does it job and isolates the suspension, then the struts don't leak too much and the car stays up. Meanwhile, pressure is leaking away through the brake valve and the brake circuit and anti-sink sphere reduce to the pressure of the sphere. If this is very low, then when the system pressure rises after start up and the antisink valve opens, there is an imbalance between the suspension circuit and the brake circuit (with the anti sink sphere in remember!) and the fluid rushes out of the suspension to equalise the pressure across the systems via the (now open) anti sink valve. You now have to wait until the height corrector responds, and more pressure is allowed into the rear suspension to stabilise things at normal height. Note that if the anti sink sphere is totally flat (ie punctured) this will not happen, since LHM is pretty well incompressible, and the pressure will rise very rapidly without too much fluid having to flow into the brake circuit.

A read of Gabors excellent technical guide (google it) is well worthwhile!