Sinker FDV hiss?

This is the Forum for all your Citroen Technical Questions, Problems or Advice.

Moderator: RichardW

Post Reply
mirafioriman
Posts: 356
Joined: 15 Jan 2011, 23:35
Location:
My Cars:

Sinker FDV hiss?

Post by mirafioriman »

Reading another post on here got me thinking;

My early Xantia sinker has always made a hissing noise when running at idle. It appears to start after the pump cuts out for the first time after the pressure has been built up and the car has risen to normal ride height.

I think (although I'm not totally sure from memory) it goes away when the pump cuts in again.

Is this a normal Xantia trait?
Former Proud owner of a 1994 Citroen Xantia 1.9d and BX 19RD

Now driving an Alfa 159 but god I miss the Xantia!
aerodynamica
Donor 2023
Posts: 1299
Joined: 26 Dec 2007, 18:10
Location: Glasgow
Lexia Available: Yes
My Cars: 2008 C5 Exclusive Tourer
1993 Xantia 1.9 TD VSX Mk1 Sinker A.K.A Slugmobile 13'
'Old Katy'
previous convictions: totaling 52litres of LHM in one go:
1968 ID19B 'Old Polly' Stellar white
1993 Xantia 1.9 TD SX Mk1 Sinker Silver
1992 XM 2.0 SEi Turbo Manual Anthracite Grey
1982 CX 20 Pallas 'Old Goldy'
1993 XM 2.1 SD Auto Light blue
1993 Xantia 1.9 TD SX Mk1 Sinker light Blue
1982 BX 16 TRS 'Cyril' Vallelunga Red
1995 Xantia 1.9 D SX Auto Dark green
1977 CX 2400 Pallas C-Matic 'Aphrodite' Regatta Blue
1982 GSA Pallas SE Silver Pearl
1980 CX 2000 Reflex Vallelunga Red
1978 CX 2400 Pallas C-Matic 'Prometheus' Midnight blue
1984 BX 14E 'Cecil the slugmobile' Maroon
1987 Fiat Panda 'the mighty panda'
x 97

Re: Sinker FDV hiss?

Post by aerodynamica »

The hissing sound is a normal trait of the first sinker Xantias with the pump-FDV-regulator combination. The same as BXs with PAS and all Xms up till between 1996 and 1998 dep on engine type.

What does vary between them is just how often and when it makes the sound. I can make my Xantia do it by causing the regulator to cut it while I have the steering wheel turned with a little bit of pressure. It'll do long, loud hisses that accompany the build up to the cut out of the regulator.

My old BX Mk1 however didn't need the steering touched as it made the sound with cut in but only if the revs were raised above idle!

XMs make the loudest hiss and it seems they'll do it regardless of revs and steering (I think turning the steering can stop it instead) but even so, it varies between different examples of the same model as my Dad's old Xantia 1.9D back in the 90s only ever made short hisses from time to time. I recall XMs when new would hiss for ages and it was quite noticeable.

I also think it depends if it's on a petrol or diesel engined car as the idle speed and torque might differ.

My big question on this is why does it do this? Wasn't there a way of 'silencing' this characteristic by engineering the dimensions of whatever part of the FDV causes it? I still like the sound though - it reminds you that there was a whole layer of extra stuff in a Citroen back in those days..

I analised the FDV functionality from the original Citroen documents for training for the BX (somewhere on line) and it seems that the there are 4 states of the FDV's operation: one is where the regulator cuts in, no steering action,
one is cut out, no steering action,
then cut in with steering action,
cut out with steering action.

The first state is the simplest as the pump flow feeds the FDV which taps off 1/4 flow to the PAS pinion valve and the remaining 3/4 goes to the regulator. no valve in the FDV moves in this.
Second state is the same but the return from the regulator having cut out feeds into the FDV via another connection (I think to make a pump supply available to the steering via the priority valve part of the FDV), the flow pressure of the feed in from the pump to the FDV is reduced at cut out. The short hiss before cut out is the pressure peaking just before cut out as it is metered through a tiny hole in a disk inside the first FDV slide valve. This isn't the hiss that is loud though.
With steering action, pressure builds in the pinion valve supply that causes the first valve to move, this changes the priority to the steering where the 3/4 flow goes to the steering and the 1/4 now goes to the regulator. If it then cuts in, with this new flow arrangement -I think- that with the pressure peak you get just before regulator cut out the 3/4 to the steering going through the metering port and the moved first valve causes noise as it peaks and with the balance between the two flows with a just-about-to-stop-steering-at-peak-pressure. Also, the feed from the regulator return just starting to feed too at cut out I reckon it's the point where pump pressure peaks and all the valves are making their change over to their rest state.

So it only hisses loudly in this one state that's why just moving steering isn't enough to do it as the cut out has to be happening at the same time.. Well I think this is the case for the Xantia. It doesn't explain why XMs make the same noise without touching the steering wheel and XMs use the exact same FDV valve part as the Xantia. BXs use an FDV with a different 'full lock' pressure relief setting due to having a different steering ram. :-D

Anyway, long story short: it's a normal characteristic.
Graeme M
2008 C5 Exclusive Tourer 2.0 HDi
Online
User avatar
Mandrake
Posts: 8614
Joined: 10 Apr 2005, 17:23
Location: North Lanarkshire, UK
My Cars:
x 664

Re: Sinker FDV hiss?

Post by Mandrake »

Hiss in the hydraulic system is easy to explain - high velocity oil flow through narrow or deliberately constricted passages. It's the same thing that makes a cold tap hiss when you turn it on, and causes a toilet cistern to hiss more loudly just before it cuts off. (On the older non-bistable sort that gradually close the valve)

The FDV valve is subject to the full high volume flow of the HP pump and its design must introduce a deliberately constricted path to balance the flows to PAS and regulator, hence the noise.

It could well be the noise that was one of the reasons for going to the 6+2 pump design in the later models. I've only driven one sinker and the hiss was rather loud on that one, I would have found it annoying if it was mine. :lol:
Simon

1997 Xantia S1 3.0 V6 Auto Exclusive in Silex Grey
2016 Nissan Leaf Tekna 30kWh in White

2011 Peugeot Ion Full Electric in Silver
1977 G Special 1129cc LHD
1978 CX 2400
1997 Xantia S1 2.0i Auto VSX
1998 Xantia S2 3.0 V6 Auto Exclusive
User avatar
CitroJim
A very naughty boy
Posts: 49518
Joined: 30 Apr 2005, 23:33
Location: Paggers
My Cars: Bluebell the AX, Polly the C3 Picasso, Pix the Nissan Pixo, Propel the duathlon bike, TCR Pro the road bike and Fuji the TT bike...
x 6156
Contact:

Re: Sinker FDV hiss?

Post by CitroJim »

Thanks Graeme for your dissertation on FDVs; excellent :-D

It's a nice characteristic. It sinks and hisses just as a proper Citroen should :-D 8-)

I'm very interested in this as I have an XM that hisses like a deranged snake. Mine indeed does it with the steering straight ahead and ceases immediately the wheel is moved. PAS is is light as a feather but I have quite a fast regulator tick at times and other symptoms that make me suspect the accumulator is past its best. If you see what a job it is to get at on an LPG'd TCT then you'll understand why I've not checked it yet :lol:

An oddity of mine is that the hissing stops instantly the steering wheel is moved and/or if the engine speed is raised just above idle but then again I do hear the hiss at times when under way...
Jim

Runner, cyclist, time triallist, duathlete, Citroen AX fan and the CCC Citroenian 'From A to Z' Columnist...
davetherave
Posts: 880
Joined: 01 Apr 2009, 21:06
Location: Norwich
My Cars:
x 4

Re: Sinker FDV hiss?

Post by davetherave »

Mine used to hiss too jim and stop when you moved the steering wheel fractionally, It doesnt since I had the FDV reconditioned by Martin!
(95) XM Silver 2.1td Exclusive.
(87) Cx 2.5 DTR T1 undergoing major cosmetic surgery.
GPZ500s
User avatar
CitroJim
A very naughty boy
Posts: 49518
Joined: 30 Apr 2005, 23:33
Location: Paggers
My Cars: Bluebell the AX, Polly the C3 Picasso, Pix the Nissan Pixo, Propel the duathlon bike, TCR Pro the road bike and Fuji the TT bike...
x 6156
Contact:

Re: Sinker FDV hiss?

Post by CitroJim »

davetherave wrote: It doesnt since I had the FDV reconditioned by Martin!
I think I might see Martin... Anyone know if a Sinker Xantia FDV is the same as an XM one? I have a spre of those and could get it overhauled for the XM...
Jim

Runner, cyclist, time triallist, duathlete, Citroen AX fan and the CCC Citroenian 'From A to Z' Columnist...
davetherave
Posts: 880
Joined: 01 Apr 2009, 21:06
Location: Norwich
My Cars:
x 4

Re: Sinker FDV hiss?

Post by davetherave »

I am almost certain it will be, its just the pressures which will be need to be set differently.
(95) XM Silver 2.1td Exclusive.
(87) Cx 2.5 DTR T1 undergoing major cosmetic surgery.
GPZ500s
cc101
Posts: 209
Joined: 31 Aug 2012, 21:02
Location:
My Cars:

Re: Sinker FDV hiss?

Post by cc101 »

Very interesting thread, my Xantia sinker seems to hiss at regular intervals when idling without touching the steering or brakes, about every 25 seconds, is this normal?

Cheers.
Xantia 1.9 TD 1993 (sinker)
User avatar
CitroJim
A very naughty boy
Posts: 49518
Joined: 30 Apr 2005, 23:33
Location: Paggers
My Cars: Bluebell the AX, Polly the C3 Picasso, Pix the Nissan Pixo, Propel the duathlon bike, TCR Pro the road bike and Fuji the TT bike...
x 6156
Contact:

Re: Sinker FDV hiss?

Post by CitroJim »

Thanks Dave, so tell him it's for an XM then, excellent :-D

CC101, yes, a hiss like that is perfectly normal :-D My old Sinker was just the same. In fact lots of people knew when I was coming - they could hear the hiss before I came into sight :lol: :lol: :lol:
Jim

Runner, cyclist, time triallist, duathlete, Citroen AX fan and the CCC Citroenian 'From A to Z' Columnist...
steelcityuk
Posts: 1053
Joined: 03 Jul 2006, 21:51
Location: not applicable
My Cars: not applicable
x 1

Re: Sinker FDV hiss?

Post by steelcityuk »

My XM hisses like a steam train which gets some funny looks from pedestrians at crossings. During normal driving there's a very brief hiss. My brothers BX never hissed constantly, just the occassional hiss followed by a phut.

Steve.
not applicable
aerodynamica
Donor 2023
Posts: 1299
Joined: 26 Dec 2007, 18:10
Location: Glasgow
Lexia Available: Yes
My Cars: 2008 C5 Exclusive Tourer
1993 Xantia 1.9 TD VSX Mk1 Sinker A.K.A Slugmobile 13'
'Old Katy'
previous convictions: totaling 52litres of LHM in one go:
1968 ID19B 'Old Polly' Stellar white
1993 Xantia 1.9 TD SX Mk1 Sinker Silver
1992 XM 2.0 SEi Turbo Manual Anthracite Grey
1982 CX 20 Pallas 'Old Goldy'
1993 XM 2.1 SD Auto Light blue
1993 Xantia 1.9 TD SX Mk1 Sinker light Blue
1982 BX 16 TRS 'Cyril' Vallelunga Red
1995 Xantia 1.9 D SX Auto Dark green
1977 CX 2400 Pallas C-Matic 'Aphrodite' Regatta Blue
1982 GSA Pallas SE Silver Pearl
1980 CX 2000 Reflex Vallelunga Red
1978 CX 2400 Pallas C-Matic 'Prometheus' Midnight blue
1984 BX 14E 'Cecil the slugmobile' Maroon
1987 Fiat Panda 'the mighty panda'
x 97

Re: Sinker FDV hiss?

Post by aerodynamica »

And yet my CX is nearly silent from the exterior despite all the extra hydraulics for the DIRAVI steering. On the inside however! the steering wheezes in one direction and hisses in the other which causes much amusement to new passengers (after they get over the dashboard and ride sensation that is - which they don't!)

Re. the Xantia Vs. Xm FDV parts: I am certain that they are an identical part with the same pressures. I'm sure it's the green painter BX FDV that is set to a lower (or is it higher :o ) pressure for the full lock pressure limiter. If you fit a XM/Xant FDV in a BX it makes the PAS ram explode at full lock (or vice versa :-D ) one of the guys on BX club found this out a few years ago!
Graeme M
2008 C5 Exclusive Tourer 2.0 HDi
Post Reply