Air bubbles in the LHM gives harsh ride?

[Mandrake]

Simon I really dont think its a question of small cumulative air leaks in the return lines.

The fact that hydraulic oil escapes from a high pressure point out into free air, makes for oil foam build up.
Remember that in this context good and leakfree return lines are to be considerd as 'free air' - compared to the situation from where the oil escapes.
Best example is a HC, where the HC rod (valve) has moved to release pressure from the suspension. If you try find one of these return lines, then lead it separately to a jar, you will recognize this oil foam ...

I agree in general - there will be some foaming as you describe, but the filter should be able to cope with this. However what I sometimes see through the piece of clear return hose I have in the return line is large amounts of obvious bubbles - as opposed to foaming which is lots of tiny bubbles. (Which I also see sometimes)

I don't think there is only one source of foaming/bubbles in the return system.

The foam is air bubbles trapped in the oil by its surface tension.
If this foam is allowed to recycle - even any number of times - through the pump - then you can imagine what happens after some driving : no hydraulic component will act quite as predictable as it should ...
Because hydraulic oil mixed with that amount of air does no longer act as a pure fluid !

The 'fluid' is then compressable - because of the air

Completely agree!!

The question is, what to do about it. If we assume there is already foam/bubbles or both returning, at the moment the return pipe exits near the bottom of the tank at roughly the same level as the inlet pipe for the pump - which is also near the bottom. If there are enough bubbles or foaming to overwhelm the filters, the pump sucks them up. (I've definately seen this happen)

It can take quite some time for the tiny bubbles that are piped into the bottom of the tank to slowly work their way to the surface and pop. Minutes in fact when I've timed it...

Pedro's idea is that if the oil is made to enter the tank ABOVE the level of the LHM, but in such a way that it doesn't splash or foam up in doing so, it should prevent the bubbles being drawn into the pump - it doesnt matter if there is a bit of foaming or bubbling on the surface of the oil, as there will then be none near the bottom of the tank where the pump draws its oil from, since the air bubbles wont travel downwards!

In other words, lets use gravity to help seperate the bubbles...

Regards,
Simon

[AndersDK]

Yes I certainly agree with Peters idea of moving the foamy/airy LHM away from the pump feed take up in the reservoir.
In fact I'm quite anxious to read reports on the outcome of this simple modification.

It is rather strange though, that this air problem does not seem to be consistent. It seems to be big problems in some cars - but not in others.

[Mandrake]

Yes I certainly agree with Peters idea of moving the foamy/airy LHM away from the pump feed take up in the reservoir.
In fact I'm quite anxious to read reports on the outcome of this simple modification.

Me too. And after all the strife I have had trying to pin this problem down I will definately be trying it myself.

It is rather strange though, that this air problem does not seem to be consistent. It seems to be big problems in some cars - but not in others.

It's not even consistent on the same car! Some cars don't have this problem, some seem to have it all the time (hi bernie!!) and some like mine it seems to be intermitant.

My car varies from almost perfect comfortable Citroen-like ride some days to awful bone jarring harsh ride on other days, and has ever since I've had it despite extensive work to the suspension.

Just last weekend I fitted new droplinks - immediate massive improvement in the ride, all harshness at the front gone, and yet a mere 5 days later the ride is harsh again... (although a bit better than before on some surfaces, so the droplinks did make some improvement)

Any kind of work on the suspension (which invariably requires depressurizing the suspension) seems to give this temporary good ride which then goes away...

Believe me, there are a number of people who are literally banging their heads against the wall in frustration trying to pin down this problem, me included....

And if it's really as simple as return air being sucked back in by the pump there will be a few red faces after all the money spent on other parts......

Regards,
Simon

[JohnCKL]

Maybe should just saw off the long piece of return pipe going downwards but that will be a permanent mod. Cut it off just below the LHM surface to prevent foaming. Then the returning LHM will NOT drain down to be sucked up again but just disperse on the surface. Any one willing to try that? LOL!

[Mandrake]

Maybe should just saw off the long piece of return pipe going downwards but that will be a permanent mod. Then the returning LHM will NOT drain down to be sucked up again but just disperse on the surface. Any one willing to try that? LOL!

I thought about that too....

The problem I can see is that if the oil is flowing in a downwards direction from the cut off tube it is still going to have enough downwards velocity when it hits the surface to (a) generate froth and (b) flow down into the bottom of the tank generating convection currects that will mix everything up and send bubbles to the bottom.

What I think would work best - if the filter wasn't there - would be if the pipe exited against the side of the tank, above the LHM level, pointing along the side of the tank, away from both the pump inlet and the filler hole.

That way the oil will run along he edge of the tank clinging over quite a wide area, and then down to the surface in a gentle low velocity way that will prevent a narrow stream of oil burrowing under the surface.

The problem with this is the return filter - I cant see any way of doing this within the confines of leaving the filter in place and operational. Still, a U pipe within the filter may be enough to prevent bubbles being forced under the surface to the depth of the pump inlet... I'll have to pull the tank riser out of mine and have a look at the dimensions....

By the way, I don't see how you could cut the pipe off just below the surface - as the level of the oil in the tank changes dramatically depending on how much oil is in use in the suspension - load up the car and the oil level in the tank will be lower...etc

Regards,
Simon

[JohnCKL]

By the way, I don't see how you could cut the pipe off just below the surface - as the level of the oil in the tank changes dramatically depending on how much oil is in use in the suspension - load up the car and the oil level in the tank will be lower...etc

Yes, after thinking for a while, the length of internal end return pipe takes into account the changes in LHM level when the car is put on high or low level, the level is not static.

[pprado]

I was thinking about obtaining a second-hand reservoir and sawing off the whole tube. I think that could improve things out with the return filter still in place.

On the other hand, the U-tube may be simulated with the filters just by closing the lower portions of the return tube... That way the LHM would need to go up and exit the filter above the surface. But it can create some backwards pressure.

I still think that the best bet will be comprised of:
- Obtaining another return filter
- making a hole for the U-tube on it, and assembling it sealed on place
- putting a filter on the end of the U-tube

Running the tube sideways seems to be good too.

Next thing I need to do is to correct the ride height. Front is too high and rear is too low.

Please let me know if you want me to run any tests...

[pprado]

I would like to shoot a thought about the air bubbles.

I saw very tiny bubbles flowing before... but after some time I could see LOTS of tiny ones. It looked like frozen refrigerant... and it was evident that bigger (although still small) bubbles did appear.

What makes it vary from hours to weeks, after maintenance, for the ride to get bad is the amount of bubble resupply that is in place.

But the ride KEEPS bad, so it suggests the fluid gets airy and keeps that way.

If it weren't by the power steering, flow would be really smaller and most probably the bubbles that could be generated by the parts would not cause problems. But the power steering would generally be responsible for amplification of the bubbles.

Could I say that the time it gets for the ride to go from good to bad, tells the "size" of the circuit that is generating bubbles? For example a bubble generated on the rear would make ride go bad one week later, and on the front could be 3-4 days later maintenance.

Does this make sense?

[Mandrake]

I would like to shoot a thought about the air bubbles.

I saw very tiny bubbles flowing before... but after some time I could see LOTS of tiny ones. It looked like frozen refrigerant... and it was evident that bigger (although still small) bubbles did appear.

Yes I see both kinds of bubbles too - the very tiny ones are probably what Anders describes - frothing caused by high pressure oil being released for example by a height corrector releasing some pressure from the suspension.

But then sometimes I see intermitant bursts of large obvious bubbles of 1-2mm in size in the pipe. I believe it is these bubbles that somehow find their way in through air leaks in return piping somewhere.

What makes it vary from hours to weeks, after maintenance, for the ride to get bad is the amount of bubble resupply that is in place.

But the ride KEEPS bad, so it suggests the fluid gets airy and keeps that way.

Well what I think happens is this - when you do Citrerobics you flush out any air bubbles in the suspension, and in fact this is the whole reason to do so - to expel any air that has entered the system during maintainance such as sphere changes. (The pocket of air trapped when screwing on a sphere has to be removed somehow...)

On an older Citroen that sinks overnight all the suspension pressure is bled away overnight so the suspension is self bleeding. Any small amount of air that got pumped into the suspension that day gets expelled.

However on an anti-sink model during normal driving and use the suspension doesn't lose pressure overnight - a little bit of height yes, but there is still full suspension pressure there all the time. Any bubbles of air will accumulate at the heighest point when the car sits - on the front suspension this would be near the top of the strut tops.

To expel the air you need enough flow at a fast enough rate to push the bubbles from here all the way past the height corrector, from which point it can't return.

On a HA2 model this is a big problem because you have long large diameter pipes from the strut tops down to the HA2 control block by the radiator, and the bubbles must then travel from here up around the side right back to the height corrector - considerable flow is required to do this, basically going from maximum height to minimum is required.

Almost 2 metres of 10mm diameter pipe and then another 1.5m metres of 2.6mm pipe must be travelled to reach the height corrector.

Normal height corrections of passengers getting in and out is not enough oil flow, so the bubbles travel back and forth in the pipes but remain trapped in the suspension and will settle in the same location again.

Now imagine that for whatever reason small amounts of air are being drawn into the pump - every time the car makes an upwards height correction (passengers getting in) some of this "airated" oil will go into the suspension, but once there past the height corrector the air will gather at the high spots.

So over a period of days the amount of air in the suspension will increase and finally reach an equilibrium. The more air is being drawn into the pump the sooner this will happen.

Lots of air being sucked in - the ride will become harsh in hours. (I've had this happen before) Small amounts of air - the ride will become harsh after a few days or a week...

Basically the problem is that air can get into the suspension by itself, and will accumulate there over time, but can only be fully purged by Citrerobics on an anti-sink model...

If the amount of air being drawn in is quite small Citrerobics will reduce the total amount of air in the suspension (even if not all air is eliminated) so the ride will improve for a while.

However I've found that if at the time you are doing Citrerobics there are large amounts of air being sucked in, it can actually make the ride worse or give no improvement, because the fresh oil going into the suspension is as badly airrated as what was already in there...(or worse!)

If it weren't by the power steering, flow would be really smaller and most probably the bubbles that could be generated by the parts would not cause problems. But the power steering would generally be responsible for amplification of the bubbles.

Maybe - but remember the 2 pistons that power the suspension and brakes are pumping all the time too. When the regulator switches to bypass mode this oil is recirculating back from the regulator to the tank as well.

Also the flow from the power steering is maximum while straight ahead, and reduced while cornering.

Could I say that the time it gets for the ride to go from good to bad, tells the "size" of the circuit that is generating bubbles? For example a bubble generated on the rear would make ride go bad one week later, and on the front could be 3-4 days later maintenance.

Does this make sense?

In my experience the quantity and size of the bubbles are directly proportional to how quickly the ride becomes bad again, and how bad it gets. Lots of obvious bubbles = ride becomes poor very quickly, and becomes VERY poor.

Regards,
Simon

[bernie]

I'm still here Simon

Getting excited about the current scribings

One thing I tried very early on, just to tie up a lose end. After fitted a new pump I fitted clear tubing to both inlet and outlet. I can confirm that not only was air bubbles present in the return pipe BUT they were also present in the outlet pipe towards the pump.
On spotting this I sealed the round plastic clip holding on the top of the tank outlet with glue but the bubbles persisted.
I am firmly of the opinion that the frothing in the tank is causing this problem after spending a fortune in new parts.
Simon, my tank has ONE large return to the tank.

Keep talking guys

[Mandrake]

Now the part that will sound crazy.

Clicking has increased to *more* than 4 minutes,
Steering is REALLY light as anyone would expect on this kind of car,
STOP light disappears BEFORE the oil light,
The boot-sitting test WORKS on my car...



I am still incredulous of all those things. As a friend of mine said - Could Citroen miss this that way?

Ok I don't want to get anyones hopes up, but tonight I tried out an idea. I already had a loop of clear hose in the return line, so I disconnected it from the tank and decided to feed it in the top of the tank:

http://homepages.igrin.co.nz/simon/imag ... n-pipe.jpg

The pipe is set up so that the end of it is about 1 inch below the level of the tank ceiling, angling away from the pump inlet, with plenty of tape keeping the pipe secure and in position. The exit of the pipe is above the LHM level at normal ride height.

In this manner there is a little bit of gentle bubbling around the edges of the surface but (hopefully) no bubbles finding their way deeper where the pump draws its oil from.

Clearly a very temporary testing only solution - because the lid is open on the tank oil might slosh out (although it hasn't yet, even on tight cornering) and dust and dirt could get in. (I'm not driving on any unsealed roads)

After doing this I did two rounds of Citrerobics (right up then right down twice then back to normal height) and then went for a drive.

WOW!!!

Yes, most times when I do Citrerobics there is a temporary ride improvement, but this time the improvement was MASSIVE from only two up and down sessions.

Almost all traces of harshness on most surfaces gone from the front suspension. Harshness over small ripples is also gone, however there is still some chattering/rattling from the front left over deep manhole covers or very large ripples, but I think I know what that is.

(The hydractive pipe from the left strut has become unattached from its clamp on the inner body wing, AND I've discovered the two rubber insulated clamps along that pipe to the left of and in front of the battery are both MISSING the bolts that are supposed to secure them, thus allowing the pipe to chatter against the body. )

There is still a little bit of harshness at the rear (although it is greatly improved) but I think that is due to the rear arm bearings needing doing.

Other things I notice - damping and body control feels much better, the car feels a lot more stable on undulating roads, less body roll, steering feels a bit lighter (slightly) and brakes also feel a bit sharper. (This car has always had problems with the brakes not being sharp)

As well as that the STOP light is going out VERY quickly - only 2 seconds after a couple of hours standing, with the back beginning to rise almost immediately. Previously it was taking MUCH longer for the light to go out and to start rising...

Basically most of the things Pedro noticed.

I can easily understand why the ride would improve, but I honestly can't see how lack of air bubbles could have so many other effects like the stop light going out sooner ??

Of course its early days yet and I need to observe the behaviour of the car over the next week to see if I'm not just deluding myself for the umpteenth time with another temporary improvement in ride, but I thought people might be interested to know....

Regards,
Simon

[pprado]

WOW!!!

This is getting nice...

As well as that the STOP light is going out VERY quickly - only 2 seconds after a couple of hours standing, with the back beginning to rise almost immediately. Previously it was taking MUCH longer for the light to go out and to start rising...

Basically most of the things Pedro noticed.

I can easily understand why the ride would improve, but I honestly can't see how lack of air bubbles could have so many other effects like the stop light going out sooner ??

You didn't mention if the clicks got improvement... however on mine they did.

Think about the accumulator sphere with LHM only.

When it is being pressurized, the pump sends oil until its pressure is about 175psi. When the circuits need pressure, the acc pressure drops until at 145 psi it needs to be repressurized.

And what if you pressurize with air? Certainly, the needed air volume to reach 175psi is much larger!

So with a non-homogenous mix of air and LHM you get erractic clicking.

When the circuits come "get some pressure", if they remove only air, the sphere will still have a large volume of LHM left and thus real pressure - delaying the click. However if they get only LHM, there will be more air on the sphere, and for the same volume of air you get much less pressure...

Of course its early days yet and I need to observe the behaviour of the car over the next week to see if I'm not just deluding myself for the umpteenth time with another temporary improvement in ride, but I thought people might be interested to know....

Regards,
Simon

I am on the same side here. Still needing to wait to see if this is not temporary. However, there is one sign of it being permanent... I periodically check how is the return flow and it is NOT getting airy. Fingers crossed!

(By the way I realized suflair may not be common outside Brazil... It's a chocolate bar that is full of bubbles (airy). Great marketing shot... you pay more for less chocolate...)

[CitroJim]

This has become one of the most interesting threads on the forum to date The depth of knowledge coming out in this thread is nothing short of amazing and worthy of a thesis

Recently, I hydraflushed my Activa and cleaned the filters. they were incredibly dirty and near to being totally choked. The difference has been quite spectacular and I'm seeing all the same results as you Simon and Pedro For an Activa, the ride is really quite pleasant.

What is more, it seems to be holding. I have about 300 miles to run before I drain the Hydraflush and refill with Total LHM. It will be interesting to see if the effects last.

Going on your point Anders, Hydraflush appears to be thinner than LHM and have a weaker surface tension. This may help matters. Did you really mean what you said about adding a couple of drops of dishwasher rinse-aid to the LHM Anders?

[MikeT]

By the way I realized suflair may not be common outside Brazil... It's a chocolate bar that is full of bubbles (airy). Great marketing shot... you pay more for less chocolate

Hola pprado 8)
We have an similar chocolate in the UK called Aero but they still have to label the net weight....

I am totally in awe and fascinated by your LHM experiement reports, well done and thank you very much for sharing this in such detail. Keep up the brilliant work and I hope you find the solution you've been working towards.
Chau,
Mike

[AndersDK]

Going on your point Anders, Hydraflush appears to be thinner than LHM and have a weaker surface tension. This may help matters. Did you really mean what you said about adding a couple of drops of dishwasher rinse-aid to the LHM Anders?

Yes Jim - I was dead serious on this !
One of my running BX'es will candidate as a guineapig as soon as I've read the label for contents and tested it in a jar with LHM

You are right that Hydraflush appears to be thinner than LHM at the same ambient temperature. This could VERY well be a pointer to what most of us experience shortly after adding the hydraflush : appearantly a much better ride.
Then later when reverting to clean LHM : things more or less back to 'normal' after a while.

I wish I had some deeper knowledge on Carbon-Hydrogens as lubricants