AL-KO Air Rides Fluctuating Pressure Readings

I've mentioned this before in other discussions...

I have an odd problem with our AL-KO air rides in that the pressures fluctuate on the dual dials, having monitored them since being fitted and trying at different pressures I currently run them at 3.5 bar as this seems to give the best ride.. I've noticed though after traveling that the pressure reading on the left and right dials can fluctuate and be higher or lower than each other, but more concerning than these slight variations for example it can sit on our drive for 2-3 weeks at 3.5 bar and double checking this before setting off it can be as high as 4 bar when I check again after a long run to our destination... it seems fine if it's parked up it's just during or after traveling it seems affected.

Can someone confirm if it's normal (I suspect not) for the pressures to fluctuate, as I intend to contact AL-KO for their advice while the units are still under warranty. When Auto-Sleepers fitted the air rides I noticed the next day it had dropped .5 bar... as we were still in the area we took it back and they said it might not have sealed on one of the pipes and they increased the pressures to 5 bar and left it sitting for a couple of hours and said it tested fine, but I've had this ongoing fluctuation since and I'm beginning to wonder if I've got a dodgy setup somewhere... if it was just losing pressure then obviously I'd know there's just a leak, but as it's increasing in pressure as well it just doesn't make sense

CC

I think the first thing we need to know is, do you know the pneumatic circuit/s of the system, can the left side be pumped up different to the right?

If so, can they then be cross-connected, i.e. equalised so both have the same pressure by adjusting the ball-valves.

Dual fill valves & dual gauges result in many more joints & potential leak points, which may give funny readings.

I designed & built my fill/air manifold to be simple by having only 1 fill valve, 1 gauge & L & R outlets to the airbags, the system can be filled by

opening both valves to a set pressure, which gives equal on both sides, OR over-pressurising, shut one valve & let the other down to the desired, then

shut that valve, open the other & let that down to the desired, this of course, results in a difference side to side to allow for odd loadings etc.

The gauge can then show amount of air in each side depending on which valve is opened, BUT, I always close both during running. I think if left open,

I too would get funny readings.

It stands to reason that if your valves are left 'open' things like van-lean, air-temp etc. can have an effect on gauge readings, & to my mind, the only

thing that can INCREASE your pressures is loading of the van & air-temp, as any leaks can only reduce it.

Mine are Dunlop dual bags (4 in all ) but they can't be that different.

I have a similar set up to Modelman except that I have single airbags, not double.
I would expect the pressure to increase after a decent run as the air will have warmed up and expanded, although this is something I have never checked.
My system does lose air over time but I have never worked out a pattern, I just top it up when required.
Unlike Modelman, I keep my valves open when running to equalise the pressure across the back axle, to my way of thinking, if I suffer a sudden pressure loss, I would rather both sides went down together rather than just one side going down and possibly having a sudden effect on the steering.

Frank

Hi there,

Good old "Boyles Law" states that P1 x V1 x T1 = P2 x V2 x T2 where P=Pressure, V=Volume and T=Temperature Absolute.

Within any air-suspension systems the relationships between these three factors will change dramatically as the vehicle bounces around on the road and the suspension changes shape (i.e. changes volume), changes the pressure and does work (which will manifest itself as an increase in temperature).

When two totally independent systems are set up in identical circumstances then the P1V1T1 parameters will start off identical; but after only a few miles of work I would imagine that they could be significantly different.

The factors affecting the difference will be:

o Unit load. (Very few vans are loaded so that the weight on both rear wheels are identical. The unit carrying most weight will do more work, get hotter and show a higher pressure.)

o Unit movement. (Very few vans have perfectly matched springs and very few roads are perfectly smooth or have identical surfaces across their width. One unit will therefore do more work than the other and register a higher temperature and higher pressure.)

o Ambient temperature. (I would expect the unit on the "sunny" side to be at a higher temperature and higher pressure than the one in the shade.)

In view of this I can see one unit showing a higher pressure than the other one at any given time whilst on the move.

Assuming that the ride in the vehicle is OK I would think that the key question is "Do both the units return to the same 'start' condition when the van has stopped and there has been time for everything to get back to equilibrium?" If the answer is "Yes." then I think everything is OK.

If the answer is "No." then I suspect that there is a leak on any system that returns to a lower pressure (assuming that the temperature hasn't dropped).

Hope this helps.

Best regards,

Agree with the others regarding temperature fluctuations.

I understand the initial drop in pressure will be due to settling in, or thats what I was told when we had the Airides fitted.

The way to check for leaks, look at the tube connections on the air bags around the compression fittings. Is there any white deposit on the outside of the pipe ?
Understand a pressure test using French Chalk is used when the bags are made so any leaks can be seen.

I have the same issue with mine. - Indepandant circuits, 2 guages.

1 I pumped up both sides to about 3 bar and let it stand overnight.
2 I reduced pressure in both sides to 2 bar
3 Drove 50 mile to site and set up
4 One side reading 2 bar the othe reading 3 bar
5 Adjusted so both were 2 bar.
6 Hours later the one which had stayed at 2 bar now just over 2 bar, one which had gone up to 3 and I had reduced was now below 2 bar.

I assume some slight increase in pressure due to driving and warming up. However I believe the main reason for the change is the site conditions. the van was pretty level on site, but by using chocks the wheels (front only) would not have been level.

I noticed that the rear end appeared to be raised when trying to level up and looking at the wheel / wheelarch gap the van looked high at the back.

I now intend to play with pressures on a level piece of ground to get the van sitting level with a normal load and then try that for a few journeys (without further fiddling) to see what happens.

Er....... I wouldn't recommend that!

If the suspension is designed to operate at "x" Bar when being set up then that is what the design engineer wanted.

If you start changing things away from the advice given in the Manual you are straying into unknown territory and like we all know from watching the movies that it always a dangerous place to go!

In addition to this, there is legislation that insists we keep our tyre-pressures equal on either side of the vehicle to ensure that we get the same feel and performance as the load swings from side to side as we drive round bends. I'm pretty sure that the same logic can be applied to air-suspension units.

Over the years I have witnessed some glorious cock-ups where the perpetrator (including myself) finally confessed and said "But all I did was ...... " and in almost all of these cases they (I) was trying something that the design engineer hadn't reckoned on!

Tread carefully.

Best regards,

Ian

Thanks for all the replies everyone... seems it is expected from reading the replies that a degree of pressure fluctuation is to be expected and perhaps I'm just being overly concerned

modelman wrote:

I think the first thing we need to know is, do you know the pneumatic circuit/s of the system, can the left side be pumped up different to the right?

If so, can they then be cross-connected, i.e. equalised so both have the same pressure by adjusting the ball-valves.

Dual fill valves & dual gauges result in many more joints & potential leak points, which may give funny readings.

Hi Modelman..... Yes you can alter the pressures differently for either side, it has two air inlets for left & right side as shown in this pic

[You must be registered and logged in to see this image.]

boxerman wrote:I would expect the pressure to increase after a decent run as the air will have warmed up and expanded, although this is something I have never checked. My system does lose air over time but I have never worked out a pattern, I just top it up when required.
Unlike Modelman, I keep my valves open when running to equalise the pressure across the back axle, to my way of thinking, if I suffer a sudden pressure loss, I would rather both sides went down together rather than just one side going down and possibly having a sudden effect on the steering.

Frank

Thanks Frank....

I'm not really experiencing air loss but just the fluctuations during or after a journey, set at 3.5 bar before setting off it has been over 4 bar upon checking on arrival at our destination. If I release air and drop the pressures then it can then go the other way and drop slightly lower than the set reduced pressure but this is only after decreasing it after it has risen so it could well be that as you suggest the pressure expands when warmed up after a run.

On the AL-KO air tops dials there is no tap, just the air valves for each sides.

Dutto wrote:
Assuming that the ride in the vehicle is OK I would think that the key question is "Do both the units return to the same 'start' condition when the van has stopped and there has been time for everything to get back to equilibrium?" If the answer is "Yes." then I think everything is OK.

If the answer is "No." then I suspect that there is a leak on any system that returns to a lower pressure (assuming that the temperature hasn't dropped).

Hope this helps.

Best regards,

Hi Dutto....

The pressures don't usually drop back down to the pre-set pressure of 3.5 bar and have remained elevated for a couple of days after a journey on occasions, usually I make the mistake of dropping the pressure back to 3.5 bar but then a few hours later when checking again it's then dropped to below 3.5 bar (this is the only time I appear to lose any pressure) so don't think there are any leaks, otherwise it would be losing pressure frequently.

By the way you can set the air rides to whatever you desire, I've even heard of people having different pressures one side compared to the other to compensate road camber or load.... Auto-Sleepers set them at 2.5 bar when fitted and to begin with I thought this was too hard as it was bumpy, so dropped them to 2 bar and it was even worse, after a few days experimenting I surprisingly found the higher you set the pressure the better the ride gets, 3.5 to 4 bar is definately the sweet spot in our Nuevo and anything below this I just cant see the point in having the air rides fitted as they do nothing, we feel them working at a higher pressure and the ride difference is very different to a lower setting or without them being fitted.

We are off to Lincoln over the weekend so will raise them again before we leave and keep an eye on them over the next few days without adjusting them further.

CC

CruizingComet wrote:.............

The pressures don't usually drop back down to the pre-set pressure of 3.5 bar and have remained elevated for a couple of days after a journey on occasions, usually I make the mistake of dropping the pressure back to 3.5 bar but then a few hours later when checking again it's then dropped to below 3.5 bar (this is the only time I appear to lose any pressure) so don't think there are any leaks, otherwise it would be losing pressure frequently.

.............

Hi there CC,

From the above it looks as if a leak can definitely be ruled out!

If the pressure "remained elevated for a couple of days ........." I would suspect that the gauge is inaccurate, stuck or in some way 'dampened' to prevent rapid and/or major fluctuation.

In any event, it appears that you are worrying needlessly and can relax once you have decided on a "starting" pressure.

Best regards,

Ian

Reading through these posts again and with a little more thought on my own experience, I think the changing pressures are more related to the condition of the ground where the van is parked. If one corner is raised, then that suspension unit and the diagonally opposite will be taking a greater load than the other diagonal pair. This will compress the air bag a little more giving uneven pressures.
With no air (how it arrived) the handling was OK. I pumped it up on my drive (not very level) and didn't notice any change in the handling (I have now done a total of about 70 miles so don't yet know the 'norm').
If I can find a billiard table to park it on I'll try to set it up static with equal pressures and monitor changes. May be out again next weekend.
My other thought was the front to back balance. If assistance is given to the rear springs I would expect the back to rise so to level on site I will need ramps under the front.
In terms of manufacturers recommendations, it is to run from 1.8 to 2.5 bar. But if they weren't fitted, ie. using standard Peugeot suspension, that would be the same as zero pressure in the system, although I am told the minimum working pressure is 1.5 bar, presumably below this they do nothing. I also note that for a non motorhome the pressures are considerably less.. So I assume I can happily run from zero bar to the max of 3 bar, as long as both sides are within 0.7 bar of each other (from the book).

Hi there,

Let me tell you a tale that has nothing to do with motorhomes but has everything to do with making hasty "adjustments".

A man bought a brand new yacht and set sail. With the wind on the starboard side he noticed that the port shrouds (the wires that brace the mast) had gone slack; so he tightened them up.

Changing tack so that the wind was on the port side he noticed that the starboard shrouds now gone slack; so he tightened them up.

As he kept changing tack he kept making small adjustments to the shrouds and this continued until the mast was driven through the bottom of the boat and it sank!!

The moral of this story is an old proverb "Act in haste and repent at leisure!"

Best regards,

Ian

Have sent an email to AL-KO for clarification of the fluctuating pressures, not that hopeful of a response as they suggest on their contact page that you contact the fitters instead for after sales advice Will update if I get a reply.

CC

AL-KO never replied to my email.... Surprise, Surprise.....
kinda guessed this would be the case, why do these companies ignore their customers

So instead I got in touch with TOWTal the towbar manufacturers as they are listed as an approved fitter on AL-KO's website, they replied saying "this is something that happens as temperature increases during use" so it seems this is perfectly normal

Have found TOWTal very helpful, also asked them about buying a pair of replacement end caps for our TOWtal towbar and they said if I send a SAE they would put a pair in the post gratis which really is great service if they are true to their word

CC