Xantia hydraulics not ticking

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CitroJim
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Xantia hydraulics not ticking

Post by CitroJim »

My '93 Xantia seems generally fine in the hydraulic department but does not "tick". Rather it makes a hissing sound for about 5 seconds in every 30 or so when idling. This hiss seems to be when the pump is supplying pressure as it is accompanied by a very slight loading on the engine. If I set the ride height to high the hiss goes on for about 20 seconds until the height is stabilised at high. I have done searches on this forum but I cannot find this exact problem.
All the spheres have reputedly been replaced quite recently, along with a new pump. I have changed the LHM and bled the brakes. The rears had a lot of very violent air in them. There is a healthy "whoosh" noise when the pressure release screw is opened and all hydraulic functions work OK. It takes a while to sink when stopped, the "sit on the tail and feel it rise with the engine off" test works OK. LHM consumption is minimal, it rises after about 15 seconds in the morning, usually back first and the STOP light goes off after about 5 seconds from startup.
My feeling is there is either a leak around the Pressure regulator (there is a little weep of LHM around it) or the Pressure regulator is duff. Grateful all your thoughts on this.
Also, there is a niggling weep of LHM on top of the LHM tank by the sightglass that slowly makes a damp patch on the tank top. Is there a gasket or seal that needs to be replaced?
Thanks all...
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Post by DoubleChevron »

IMO.... It works well and is not leaking LHM. Leave it alone .... I don't like fixing things that aren't broken :)
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Post by Mandrake »

Very odd!
I've never heard of this happening, but really, the only thing it could be is the pressure regulator unit, from your description.
The source of the "click" on a normally operating pressure regulator comes about as there are two control shafts (a master shaft and a slave shaft) with loading springs which are configured to operate as a hydraulic version of a "bistable" latch, or schmitt trigger. (For those that know what I'm refering to [;)] )
By use of positive feedback once the threshold pressure is reached, both control shafts "snap" very quickly to their opposite positions - there is no inbetween position where there is a partial opening of the valve.
It's either fully open - feeding the pump to the accumulator sphere and the rest of the system, or fully closed - feeding the pump back through the return hose to the tank, so the oil circulates at a low pressure in a closed loop.
Typically the cut-out would happen at about 2500psi, and cut-in at 2100psi.
If high pressure oil is forced through small holes at high velocity it will hiss audibly (witness the power steering, which hisses when you turn it) so my guess is that the slave valve is jammed or otherwise not working, leaving the master valve to act like a crude, simple spring loaded bleedoff valve.
(I believe that the very first series of ID19's had a simple spring loaded bleedoff valve much like this, before the two shaft feedback design now used became universal - can anyone confirm that ?)
In that case the valve wouldn't be snapping fully open and closed, but would be partially opening, hence the hissing..
Is 15 seconds normal lifting time before the problem occured ? or has it had this problem as long as you've had the car ?
Does it have the anti-sink valves ? (I'm guessing no)
If the valve is only moving partially then it could either cause the car to take longer to pressurize (by not allowing the full output of the pump to be delivered to the system, but rather bleeding some of it off) or at the very worst case scenario it may be letting the system pressure build up much higher than normal, which could be quite dangerous.
Granted, thats worst case scenario, but I wouldn't be happy ignoring it if it was my car.
Regards,
Simon
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Post by citronut »

if regulator ticks it means your reg sphere is low on gas,of course it dependes on how low gas is to how often it ticks,as reg spere is not only an acumalater for reserve presure but it is also a damper for regulater,your hissing at these time intervelse is normal regards malcolm
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Post by citronut »

ps leak from top of tank is to much LHM no prob just makes a mess
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Post by Mandrake »

<blockquote id="quote"><font size="1" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote"><i>Originally posted by citronut</i>

if regulator ticks it means your reg sphere is low on gas,
<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">
Sorry, but this is not true.
The regulator will always "click" audibly on cut-out regardless of the accumulator sphere being gassed or not.
If the sphere is low on gas it will click a bit louder, and also more often, but that doesn't mean it wont click when the sphere is gassed. (You might not hear it from inside the car though, but you will definately hear it from outside)
<blockquote id="quote"><font size="1" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote">
of course it dependes on how low gas is to how often it ticks,as reg spere is not only an acumalater for reserve presure but it is also a damper for regulater,your hissing at these time intervelse is normal regards malcolm
<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">
First I've ever heard of hissing from the pressure regulator instead of clicking being "normal" [;)] The fact that the question is being asked in the first place after the original poster searched the forum suggests that its not a normal occurance.
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Simon
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Post by Peter.N. »

It depends what else is going on to create noise at the time that the regulator cuts in/out, I cant allways hear mine on an XM, but what I do have is an almost continual hissing noise while the engine is ticking over, this I believe to be due to low output from the pump. The reason I have reached this conclusion I will relate : From the time taht I bought the car the pump never seemed to cut out until the revs were increased, and then it would cut in and out every few seconds, I had already replaced the acumulator sphere, so I suspected the regulator which I eventually changed, at the same time I fitted another accumulator sphere, since then it still continually hisses at tickover, but if a rev the engine briefly the pump cuts out and stays out for about one minute then returns to a continual hiss, in normal driving you dont hear it any more. So I can only conclude that I had a duff sphere first time round but I now need a new pump.
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Post by DoubleChevron »

<blockquote id="quote"><font size="1" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote"><i>Originally posted by Peter.N.</i>

It depends what else is going on to create noise at the time that the regulator cuts in/out, I cant allways hear mine on an XM, but what I do have is an almost continual hissing noise while the engine is ticking over, this I believe to be due to low output from the pump. The reason I have reached this conclusion I will relate : From the time taht I bought the car the pump never seemed to cut out until the revs were increased, and then it would cut in and out every few seconds, I had already replaced the acumulator sphere, so I suspected the regulator which I eventually changed, at the same time I fitted another accumulator sphere, since then it still continually hisses at tickover, but if a rev the engine briefly the pump cuts out and stays out for about one minute then returns to a continual hiss, in normal driving you dont hear it any more. So I can only conclude that I had a duff sphere first time round but I now need a new pump.
<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">
My BX did this when I first purchased it.... 100,000+km later it's still doing it and has got no better or worst. I'm not at all concerned.
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Post by jeremy »

My BX (which is a bit slow to rise in the mornings) doesn't make any firm click but rather a hissing/rattling about 45 secs or so when it has stabilised (may be longer - I loose interest after about 30 secs)
It used to cycle at about 9 seconds and even with a new sphere it was obvious that something was wrong. The answer was that pressurised LHM was leaking from the accumulator sphere base back the way it came - ie through the non-return ball valve, and re-seating it by striking it smartly using a brass punch cured the problem.
This procedure is written up fully in many other places. I was able to do the job without removing the regulator from my BX TD.
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Post by CitroJim »

Thanks all for your very good advice on this. I took a very close listen today and the noise is certainly coming from the PR. Loved your description of the PR being like a hydraulic bistable Mandrake!Can't agree on it being a scmitt trigger though...
I've studied the operation of the DS PR in the "Hydraulicnotes" PDF I downloaded a few days ago and can see exactly how it works.
Despite the accumulator apparantly being recent, I'm going to change it, just to be sure (and having a spare on the shelf is not a bad idea I guess) and whilst there, have a go at reseating the non-return valve.
Citronut, you were right about the LHM tank being overfilled. I'd been keeping it so the brass disc was at the top red line rather than the orange coolie hat.. [:o)]
Just loving getting to grips with the hydraulics. I find this aspect of the Xantia incredibly interesting and absorbing as well as being a brilliant way to suspend, steer and brake...
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Post by Gaskin »

For what it's worth my 97 Xantia TD doesn't click, but makes a sort of short buzz every so often. Everything seems to work OK so I'm not worried about it. Unless any one else knows better of course!
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Post by citronut »

regulater sphere with gas dose damp regulater action regards malcolm
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Post by Mandrake »

<blockquote id="quote"><font size="1" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote"><i>Originally posted by citrojim</i>

Thanks all for your very good advice on this. I took a very close listen today and the noise is certainly coming from the PR. Loved your description of the PR being like a hydraulic bistable Mandrake!Can't agree on it being a scmitt trigger though...
<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">
Well, a schmitt trigger works based on a small amount of positive feedback to create a device with hysteresis - eg the on threshold is different to the off threshold. It takes at minimum two active components to generate positive feedback like this. (Can be done with two transistors for example)
In the pressure regulator the two control shafts operate each other in a positive feedback loop to provide this same hysteresis action - cut-in pressure is about 2100psi, cutout about 2500psi. This ensures that as the pressure rises, the valve closes abruptly instead of gradually closing.
On the other hand the early ID19's without power steering just had a single shaft spring loaded bleedoff valve that would have had a single pressure operating point with a variable opening. (Which would have probably hissed quietly, instead of clicking)
I remember Dad explaining why they changed to the two shaft regulator design but I can't remember the details now [:D] Something to do with reliability and long life I think..
<blockquote id="quote"><font size="1" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote">
I've studied the operation of the DS PR in the "Hydraulicnotes" PDF I downloaded a few days ago and can see exactly how it works.
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If its the later version with the two control shafts at right angles, then it is functionally identical to all the later models....(this, and the height corrector design stood the test of time and basically went unchanged for over 40 years...)
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Despite the accumulator apparantly being recent, I'm going to change it, just to be sure (and having a spare on the shelf is not a bad idea I guess) and whilst there, have a go at reseating the non-return valve.
<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">
Good idea about checking the non return valve - thats something I hadn't considered, as I havn't seen one fail before...
<blockquote id="quote"><font size="1" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote">
Just loving getting to grips with the hydraulics. I find this aspect of the Xantia incredibly interesting and absorbing as well as being a brilliant way to suspend, steer and brake...
<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">
Once you get used to the idea, you wonder why nobody else does it the same way.... [:D] Especially using a high pressure system for brakes....
Regards,
Simon
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Post by jeremy »

I think the non-return valve is responsible for just about all cases of frequent cycling when the accumulator sphere is not completely flat. In order for the regulator to cycle there must be a drop in pressure which simply means that high pressure LHM must go somewhere. There are 3 ways out from the accumulator - onward - where it either leaks or does something like raise the car, down the centre valve or back the way it came - ie past the non-return valve. If the centre valve is worn - the regulator will need replacing and the various parts will require measuring. Re-seating the ball is going to be easier than measuring the valve for wear and certainly AlanS and I have found it very effective in reducing the cycling rate.
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Post by CitroJim »

You're right Simon, it was thirty years ago now I did my electronics theroy and I'm rusty. Not much call for building discreet bistables and schmitt triggers these days out of OC71 transistors!!!
Funny that, people are quite happy to have practically a space shuttle full of electronics in a car these days but oleopneumatic - no way - far too complex. Me, I like as little electronics as I possibly can get away with; 30 years in the trade and I can't trust it. Something mechanical I can see, feel and work out from first principles how it works and how, usually, to fix it in some way or another. Can't do that with modern electronics however switched on you are.
If I had a quid for the number of people who have furrowed their brows at my Xantia saying "urrr, I'd never have one of those, bloody expensive and complicated when they go wrong" I'd have recouped the purchase price by now! Mind you, they all agree that nothing beats it for ride quality though...
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