Workaround for bubbles in LHM return flow

[ksanturion10]

Haven't gone all over this thread, nevertheless it is really entertaining .
@MatPL, you are saying, that you changed a couple of pumps, but have you tried to overhaul them before installing back into the car?

BR
Martin

[MatPL]

It is theoretically possible that a fast-flow pipe can create lower pressure sonewhere along its length (a Venturi effect?) if there is a restriction somewhere.
What you might be able to do is gently restrict the flow from this return pipe at the reservoir, and see whether the pressure in the pipe (which will be higher is you move the steering wheel) is enough for a leak to be seen/found. That leak will probably be the source of air ingress.

That's what I meant about the Venturi effect. I will do a return line on the new hoses as now I have silicone tubing not working well with LHM.

Matpl try this, You leave the car depressurise for a day to clear the bubbles . Get a thick Clear PU hose with internal diameter of the intake connector of the hydraulic pump . It must be nice tight fit without need to use any fasterner. The other end of the hose you directly insert into the LHM container without need to go into the filter but make sure its way below the level of the LHM oil.

I have already tried with the cable mounted in this way. The microbubbles continue to flow to the pump from the LHM reservoir.
I also thought the steel cable that goes from the power steering pump LHM. Its diameters are different for the ES9J4 engine. The steel hose becomes hot during operation. I suspect that by reducing the flow diameter from 6.35mm to 4.5mm and high pressure and high oil flow, it can create microbubbles that return to the tank?

@MatPL, you are saying, that you changed a couple of pumps, but have you tried to overhaul them before installing back into the car?

I checked each pump for the expenditure before installation. 1 wheel rotation per suspension gave about 1.2 ml of LHM, and 3.5 ml of LHM for power steering. As described by Citroen. The seals were replaced every time. In May I was able to buy a brand new Citroen LHM pump and the result was the same.

[ksanturion10]

Maybe you should try genuine LHM hoses, so you don't focus too much on the bubbles, and try to find some other reason for your bad ride comfort

BR
Martin

[MatPL]

Original Steering Gear / Conjector Return Hose Kit is not available. My one that I had on the car was leaky, so I had to change the hoses. I found hoses made internally from FPM / Viton. I will try to mount if the price is affordable.
Martin, what else could there be for a rough / nervous driving in your opinion with a very soft static suspension and while driving? The spheres are correct and HA has been error-free for 3 years.

[white exec]

Ride quality:
If suspension is soft while the car is stationary (static), but rough/nervous when driving, are you certain that
- tyre pressures are not too high, even by a very small amount (from memory 2.3bar FF, 1.9bar RR) ?
- the FF and RR electrovalves are actually working, electrically and hydraulically ?

When driving, is the suspension crashy/twitchy only at slow speeds, and over lateral ridges . . . or is it also harsh at speed on an open road?

If you drive while continually waggling the accelerator pedal (rapid pressing up and down) - which should force the suspension into Firm mode - does the ride stiffen up (as it should) ?

[MatPL]

The pressure is 2.4at the front and 1.8at the rear. It should be 2.5 and 1.9at.
Solenoid valves work properly when stationary and while driving. Feel that the car is leaning over long unevenness. During strong acceleration, I push back to the ground, but I have almost 230HP on the engine with manual gearbox.

The suspension works nervously then what you wrote. When driving from the side of about 100 km/h, the suspension works fairly smoothly, but it can shake as for a higher linkage. All HA sensors are working properly. Accelerator pedal, steering wheel, excessive suspension height, because I can view the LED on a regular basis. Feel that the suspension is not sagging.
I did a video of bending the suspension today. This is how he works while driving, but very nervously on fast jumps and unevenness.

[ksanturion10]

Yes, I've also noticed, that correct tyre pressure is crucial, but don't believe, that they didn't took this into account, when developing the system.
There are too many factors, that can influence the pressure in the tyres; I see, that there are newer models, which can monitor the tyre pressure in motion.

Mine is Hydro-Pneumatic, non Hydractive -> analog system. My engineering sense is telling me, that the suspension should harden at higher engine RPM, so it should be somehow flow depended. I don't have suspension ECU, that can query the speed of the vehicle, so I think it should rely purely onto the flow from the pump -> if ofcource the system is designed to harden in this way. So maybe, this is the normal situation and for the HA system, not sure.

I don't believe, that the bubbles can affect the system so much. Is there a way you can check if they are drawn into the high pressure circle after the conjecteur? To me this is highly unlikely as Icwin said, but who knows.

BR
Martin

[Hell Razor5543]

Something that can definitely affect the ride is if the suspension ride height is set wrong (I don't mean the control lever in the car; rather, if the front/rear is riding too high/low). On my basic spec Xantia (with six spheres) the front was riding too high, and she felt 'skittish'. Once this was corrected the ride felt much more stable.

[ksanturion10]

Sounds crucial too

[white exec]

Looking at those two videos, Mat, of you pressing down on the FF and RR of the car, I would say that the suspension looks much too soft - especially for a high-BHP XM - with the body going down far too easily, and by too great an amount.

Are sphere gas pressures and damping apertures all correct, for not just corner spheres, but for centre ones as well?
Note that the damping for the centre (Soft mode) spheres is in the suspension regulators (where the EVs are).
Are your regulators the originals for the car, or did you fit late-Xantia type?
If Xantia-type, did you transfer the original XM dampers into the replacement regulators?
Is anything else non-standard?

Harshness over sudden lateral ridges at low speeds is normal on these cars, unfortunately. It is the only situation where the HA suspension is less than good.

Good that you have EV LEDs fitted.

[MatPL]

Mine is Hydro-Pneumatic, non Hydractive -> analog system. My engineering sense is telling me, that the suspension should harden at higher engine RPM, so it should be somehow flow depended. I don't have suspension ECU, that can query the speed of the vehicle, so I think it should rely purely onto the flow from the pump -> if ofcource the system is designed to harden in this way. So maybe, this is the normal situation and for the HA system, not sure.

I don't believe, that the bubbles can affect the system so much. Is there a way you can check if they are drawn into the high pressure circle after the conjecteur? To me this is highly unlikely as Icwin said, but who knows.

The car's speed sensor gives information to the HA computer. The faster we go, the easier it is to put the suspension into sport mode to make it safer and it's normal and in line with Citroen's idea. In my case, when driving faster, the suspension selects bumps better. Driving at low speed with lots of twists and turns, the driving experience is rough and unpleasant.
I explain my rough ride this way:
If the LHM oil has microbubbles in the hydraulic hoses and in the actuator, to do the work, it must first compress the air in the LHM and then press the diaphragm or perform work, etc. I think that on short bumps the oil moves too slowly in the tubes to compress the diaphragm which results in a rough lagged suspension response despite soft driving on a straight road. The principle of operation is the same as with air brakes. They work late and poorly!
I can't find another explanation because I tried all the advice I got and the air is still in front of the LHM pump.

Something that can definitely affect the ride is if the suspension ride height is set wrong (I don't mean the control lever in the car; rather, if the front/rear is riding too high/low). On my basic spec Xantia (with six spheres) the front was riding too high, and she felt 'skittish'. Once this was corrected the ride felt much more stable.

I have already adjusted the height 100 times. I tried to ride lower and higher. Unfortunately, the feeling of roughness is the same, but too high it becomes unstable when accelerating hard. With a lower setting it feels softer, but it can hit the ground too often.

[MatPL]

Looking at those two videos, Mat, of you pressing down on the FF and RR of the car, I would say that the suspension looks much too soft - especially for a high-BHP XM - with the body going down far too easily, and by too great an amount.

Are sphere gas pressures and damping apertures all correct, for not just corner spheres, but for centre ones as well?
Note that the damping for the centre (Soft mode) spheres is in the suspension regulators (where the EVs are).
Are your regulators the originals for the car, or did you fit late-Xantia type?
If Xantia-type, did you transfer the original XM dampers into the replacement regulators?
Is anything else non-standard?

I had the spheres checked this Saturday weekend.
On the front corner I have the original multi-layer CItroen for the ES9V6 38at 0.6mm.
The front EV is 500cc and 73at for a while until I check my 450cc multilayer.
I have the rear corner IFHS 30RN about 0.6mm? completed to 37at for Berline XM.
The rear EV is 500cc 56at temporarily until I check out my 450cc multilayer.
I have mounted EV blocks from a late Xantia, but I moved the dampers from the XM V6.
On multi-layered spheres near the EV blocks it worked slightly less, but the rear was able to reach the ground anyway with a strong long start.
As for the other elements, I am currently driving the old H4 version on the HA computer, adapted to the new H5 type. It differs less frequently into sport mode and does not respond to the brake hard sensor.

Harshness over sudden lateral ridges at low speeds is normal on these cars, unfortunately. It is the only situation where the HA suspension is less than good.

I cannot agree with that because a few times this car has experienced a magical ride on a really horrible and rough road. I just got in in the morning and it rode perfectly for about 5km. Recently I was driving a C5 MK1 still on the original oil and spheres. I crossed the railroad crossing like a dream. I had to go back and try again because I didn't believe it. My Xm is shaking and creaking on the same railroad crossing despite good pressure in the spheres and new LHM oil. It is unfair!

[white exec]

It is sudden vertical steps (as small as 3-4cm) that XM HA suspension can struggle to smooth out, particularly a sudden downward step, producing a thud/crash of the rear end. This can be worse when the car (i.e. the fluid) has warmed up, and so damping is less.

The use of late-Xantia regulators is a significant improvement, in that it prevents sudden changes in road height from causing a hydraulic shock, which can push the standard regulators into Firm just when you meed them to remain Soft. The problem with dramatic sudden changes in road surface height remains, though. The suspension just cannot cope with this, and the tyres are left to cushion the impact - which is why Michelins, with their very pliant sidewalls, tend to be favoured.

[white exec]

Looking at your sphere list, the larger sphere volumes and the slightly higher pressures will both produce extra softness and vertical movement when in Soft mode, which probably explains your quite soft bounce test.

On the front corner I have the original multi-layer CItroen for the ES9V6 38at 0.6mm. Book lists 450/40/0.7
The front EV is 500cc and 73at for a while until I check my 450cc multilayer. Book lists 450/70/--
I have the rear corner IFHS 30RN about 0.6mm? completed to 37at for Berline XM. Book lists 400/30/0.6
The rear EV is 500cc 56at temporarily until I check out my 450cc multilayer. Book lists 400/50/--

[ksanturion10]

If the LHM oil has microbubbles in the hydraulic hoses and in the actuator, to do the work, it must first compress the air in the LHM and then press the diaphragm or perform work, etc. I think that on short bumps the oil moves too slowly in the tubes to compress the diaphragm which results in a rough lagged suspension response despite soft driving on a straight road. The principle of operation is the same as with air brakes. They work late and poorly!
I can't find another explanation because I tried all the advice I got and the air is still in front of the LHM pump.

The air into a closed hydraulic circuit always tends to go up, opposite to earth's gravitational force, so I don't really believe, that the pump can push it into the conjecteur tube and into the main HP circuits. It will rather escape trough the pump before reaching the conjecteur. But you are right, about the down sides of air present in hydraulic circuits, when it comes to compression.
I suggest you to take second good look at your first video -> something is not quite right over there. At first you start to push it down and it responds well by leveling at some constant distance from the tyre. After some time, while you are standing next to it (I guess you are not pushing it down at that time?), the car starts to rise its front, but the rear stays the same -> this is not correct. Generally if you are not on level ground, and if it has to rise the front, to make the body leveled, the back should fall . But I presume you are parked at leveled ground - nevertheless in both occasions for me there must be wrong height setting at the front, as James suggested earlier.

BR
Martin