Hi,

I'm on my first Citroen with a FDV but despite trying I can't find much out about it. The site search doesn't work on 3 letters and I've had a poke around but come up empty.

Are there any good links available so that I can find out what I've been missing these past couple of years.

Thanks.

Steve.

Dunno Steve, why not try "Flow distribution valve" instead of "FDV"?

And sorry if I'm in grandmother and egg sucking territory, but select "hydraulics" and "older" before pressing search.

Derek

Hi Steve, the "CitroenTechnical Guide" outlines the operation of the FDV,and the "Citroen Service " site under parts, xm, steering icon, steering distribution valve icon, gets you to the parts breakdown, for filters about £6 each and repair kit (identified "ball joint kit")about £34.

Robert, are these filters only available from the Citroen dealer? I've also had some recent interest in the FDV albeit on the BX as I was getting the famous problem of a constant hsssss and the regulator not reaching cut out. It stops with the familiar cut out if you raise the revs.

The FDV of the Xm and BX is the same physical part but the XM item has the steering full lock pressure relief set to a different value.

There's a bit on the BXClub forum about disassembly of the FDV including some 'beware' pointers regarding the very small disks and springs.

http://www.bxclub.co.uk/forum/viewtopic.php?t=2865

I think you can view this without signing up - apologies if you can't

I also have the .pdf files of the Service instructions if needed - someone on Frenchcarforum said the Citroen Service website had barred 'non - professionals' - could anyone confirm this?

As I understand it, if pingfukkits are not your strong point, then there may be a few elements to the FDV rebuild that make it a Pleiades job...

I need to do mine, I keep pushing through those momentarily heavy positions while turning the wheel and merrily pretend it isn't happening... lalalala

Incidentially, if you do decide to go for the rebuild, any pictures of the stripped unit would be interesting.

Ciarán

With the search not working on 3 letters I actually had a trawl through the whole hydraulic section which is what lead to this posting. As noted I did find various bits on the BX sites and Aussiefrogs. Mine maybe faulty, plenty of hissing when ticking over and the steering wheel left alone but apart from that there's not really a problem I know of, I may leave it as it is then if someone asks what the noise is I'll tell 'em it's steam powered.

Steve.

I should say that an occasional, very audible hissing noise on FDV-equipped XMs is entirely normal. The sound should however, be intermittent and always terminate on its own without having to raise the revs.

If there is a hissing noise at idle that seems to go on for ever, check that the HP pump belt is tight enough and that the HP pump LHM suction pipe is tightly secured and not drawing air as both of these affect the pump output and affect the FDV valve action.

The FDV takes the pump output and then splits it 1/4 flow to the PAS and the remaining 3/4 to the pressure regulator/accumulator. It has 4 distinct phases: cut in of regulator with steering straight, cut out with steering straight, cut in with steering wheel moving and cut out with steering wheel moving. There is a 5th state I believe where the PAS is at full lock and a single ball check valve releases the pressure.

The regulator gats 3/4 of the HP pump flow and the PAS 1/4, the PAS (i.e. the pinion valve) gets this flow regardless of the status of the rest of the hydraulic circuit, so if the suspension is at low, the FDV is jetting off 1/4 of the flow, if the PRV bleed valve/12mm bolt is open, the PAS is still getting its 1/4 flow through the PRV.

When the car is running but stationary the LHM flow is divided by the FDV. When the regulator cuts out the dumped LHM flow through it goes into the PRV again and feeds the PAS from a second inlet. I think the PRV also provides a balance between the 1/4 tapped LHM flow and the dumped flow out the regulator - both made available by the FDV. If the pressure to the PAS is higher than the set pressure needed due to the 2 inputs, the input (whether the 1/4 off the pump or the dump out the regulator - this is the bit I'm still working out!) is dumped out the FDV to the LHM tank and it's possible that this is the Hiss noise heard while no actual steering or any other movement is being made.

Because the PAS works with the 12mm bleed bolt released, and because the LHM flow from the pump through the FDV is bound to take the path of least resistance, my question is that when the gross flow of the HP pump enters the FDV and meets the metering 'jet' that takes the 1/4 to the steering and the rest goes unhidered back to the LHM tank since the bleed is open, then what force motivates the 1/4 LHM flow to power the steering? why does any of this flow go through the tiny hole to the PAS supply?

That hiss noise is loud enough to make people look! But in its occasional interruption, it's totally normal. A constant, never ending hiss is an issue though..

Hi Graeme

very interesting info, have been trying to work out how it works myself, from the docs in my flickr pages, but couldn't make enough sense from the images and poor description...

Good to know XMs with FDV shouldn't hiss continuously with the steering on the straight. Most I've seen hiss continuously, and it's loud enough to make you think "this can't have been sold like that". I've been wondering though if this hissing would be a problem in the FDV primarily or in the pressure regulator alone, or a combined thing, and how this can be tested is the big question. I know how to test a "non-DFV" pressure regulator but not an FDV one.

byebye
George

I don't actually know George, I am certain that it's nothing to do with the Pressure regulator though.

Testing is the problem.

Although it's a BX, the FDV is the same and despite fitting a brand new HP pump and retightening the belt, cleaning the filters and fitting a new accumulator, I was still getting the constant hissss at idle and still required to raise the revs to get the regulator to cut out and the hiss to stop. BUT! I'd changed the LHM back in November and decided to change it again for hydroflush (I'm keeping the outgoing hardly used LHM btw and will re use it and pass it through a coffee filter) and ensured the 12mm bolt of the regulator was tight. Result? It has stopped the constant hiss.

According to a chap on the Citroen Club forum,Malcolm, he says that when he worked on BXes in the past, he found that rubber fragments had collected in the 2 nylon filters of the FDV and blocked them. They would eventually break through due to the flow and this would leave fragments of rubber and nylon in the FDV causing the 2 slide valves to stick. There are also a number of 'jets' in the FDV - they are each a tiny disk with a very small hole in the middle. These decide how much the LHM flow is divided depending on what valve has slid and when, Having seen the size of the little hole I can't see that anything other than crystal clean fluid could work with it - My theory now it that the sudden improvement from the Hydroflush is down to the stuff being totally clean and this being a second change in 3 months, has purged the vast majority of the old grot. I'm hoping that my FDV was actually OK but the grubby LHM was to blame for a bias of flow causing the hiss all the time due to a blocked alternative route or some such. Either way, it's nearly bang up to scratch all of a sudden.

There was a guy yonks ago on Frenchcarforum with a Mk1 Xantia, again with FDV, complaining about this darned hissing all the time - he said he'd do whatever he could to fix this 'fault' and after the Citroen dealer failing to rectify it (citing such fixes as new accumulator) he said he 'had' to get rid of it due to this fault! He stated the car as having low miles, and absolutely no symptoms of fault other than the noise!

I can assure you that the Xm certainly did make the hissing noise from new - it was one of the characteristics I noticed when we went to see the car at the Citroen dealer in Lanark in 1989 - I though it sounded quite cool, like the noise was evidence of some sophisticated system making metered adjustments of some type.. But perhaps when the car is new, the sound is less frequent and lasts only a few seconds - certainly there are times where it makes the sound briefly and others where it goes on for 15-30 seconds and sounds like it's going to blow!

The BX is the same - odd hiss now and again and then the occasional long one but now it does at least cut off on it's own..

I'm actually on the look out for a spare FDV to rebuild it and swap it over but also to work out some of the remaining questions of what it's doing in action.

Hi aerodynamica,sorry have no idea if the filters are available outside cit dealers,but perhaps pleiades would oblige a service kit if approached.

Hi Robert, honestly, it's just my usual need to attempt to source the cheapest option!

Hi all

I have rebuilt my FDV and it still is very loud when i first start the car, when i drive off with the revs raised it would stop but on returning to idle it would start again untill it has warmed up (2 minutes) and then it wont do it for the rest of the day?!?!?.
This is why i rebuilt it, then got another and rebuilt that to put on, then got a new pump, and P/Regulator still with no change. Now the Turbo i have just got does it much more than my prestige, same symptoms (only at idle with steering at rest) but the hiss is a much quieter and softer sound, the prestige's hiss drowns out the sound of the engine .
When i spoke to cit they said try a new acc sphere, which isnt going to work, but out of desperation i tried a new one anyway, and it didnt work , Pleiades said that another FDV may well still do the same thing, so, reluctantly i gave up

D

I think I'll stick with it as it is, everything works OK. I'll put the effort into putting the amp and speakers in as usual. And a good set of reversing sensors - Valeo's are the best I tried up to now.

Steve.

All this talk of FDVs, heres one for you.

Steering sometimes has a heavy spot, but only at certain positions on the wheel, like 1-4 and 7-9 o'clock. You can 'push through' the heaviness, and its light the rest of the way round. The heavy spots are always at the same positions.

This seems to only happen intermittently, irrespective of revs (it persists even if you put the car in neutral and rev to 3 or 4k). The suspension and brakes seem fine, and though the pump is noisy these days, it seems to still supply decent pressure, the accumulator only clicks every 20 seconds or so, and the car is quick to rise when the adjustment lever is used.

Do these symptoms sound FDV-ish to anyone?

Ciarán

Ciaran, it wouldn't be the old dried out universal joint in the cardan shaft? - I think it only affected Xantias of a certain year but gave similar symptoms. Though you say it's intermittent so perhaps not.

I tend to think that symptoms of the PAS are down to the pump or pinion valve alone because the FDV can't allow a break in supply to the PAS as far as I can tell - FDV faults tend to affect the suspension side of the circuit more likely. A simple check though is to loosen the pressure relief on the regulator and run the engine with it loosened. The PAS should still operate as normal like this - that at least, will show that the FDV is still giving the same uninterrupted flow for the PAS.

Otherwise, you just need to overhaul one thing at a time to get to the bottom of it (like what I'm doing ) and slowly sorting it.

But I'll admit the FDV is a troublesome device!