Semi-air suspension valve settings?

ShaKen

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Apr 26, 2019
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60,211
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A few years
Following a question on another forum re semi-air suspension it got me thinking about the way it should be configured on a manual (non-compressor) setup.

I’ve fitted the Dunlop semi-air system without the con board compressor & tank and thus have a gauge with a two-way valve setup where you can isolate each airline to the 2 independent bellows (nearside / offside).

I’m of the opinion that when on the road, I should isolate each side from each other to maintain the pressure in each side.

However, another person has recommended that the valves are left open, effectively having the same air circuit across the two sides (they said that an installer recommend that) meaning that air can move from bellow (side) to the other (side).

But in my view if you leave the valves open then when cornering / turning, then natural movement due to centrifugal effect would roll the vehicle to the outside of the turn, put pressure on the bellow and thus force air into the opposite side, exacerbating the roll effect. In summary making the roll even worse.

What’s your thoughts / how do you setup your suspension?

P.S. Can everyone please refrain from turning this thread into a COVID/Brexit/Scottish Nationalist one. It would be nice to have a thread that sticks to the topic for once.
 

MikeD

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Dec 21, 2011
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On our "Compressor driven" semi air set up the two sides are totally independent of each other. We have if we filled it manually two valves in the dash of the motorhome together with two gauges.

You will often see different pressures on the gauges as the van is never the same weight either side.

DPP_0004.JPG
 
May 19, 2020
124
133
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Knaus Sun Ti 650 MEG
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Since 2020
I believe instead if you had bought a basic Dunlop system i.e no guage just two Schrader valves then the bellows will always be isolated from each other, therefore to my mind any further additions i.e gauges and compressors you should ensure when running that they remain isolated.
 
Feb 2, 2019
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Pilote G740C
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I believe instead if you had bought a basic Dunlop system i.e no guage just two Schrader valves then the bellows will always be isolated from each other, therefore to my mind any further additions i.e gauges and compressors you should ensure when running that they remain isolated.
That's what we did, bought the basic kit without the gauges or compressor. You're totally correct, both lines are independent of each other and each have their own inflation valve. Easy peasy.
 
Aug 9, 2011
225
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The OP is correct. I have the same system. I open both valves when presureising the system and then close both valves when driving.
2D47AD5F-95B7-490B-8011-841D06A277B2.jpeg
 

MikeD

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Compressor, fitting, wiring in seem a tad of a luxury. Once every few months my bike pump levels up my dials.

I agree, I would not add a pump again. We hardly change the pressures from one month to the next.

But I was new to motorhoming when it was fitted to my van and did not know any better. (y)
 

ctc

Oct 12, 2015
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What is wrong with having a row about "COVID/Brexit/Scottish Nationalist"? Apart from that I agree with all the above, I have 3.5 tons on the rear axle (with the water tanks empty) 2.5 bar in the air bags and the ride is very good.

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Apr 22, 2018
3,080
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The two sides must be separated otherwise the system will swap pressure the wrong way making things worse. As the vehicle leans to the left, this would squash the airbag pushing more air into the right airbag, increasing the lean to the left, which is the opposite to what you would want to happen.

I’m pleased to have fitted the pump as I alter my pressures a lot. Even when parked up at home, I drop the pressure to give the roof the biggest possible slope to keep the water off the roof, and also alter the pressure depending on conditions, and for levelling
 

Bobby-gg

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Out of interest, asking those that have an on board compressor - how well do you find using a rear bag only system manages with levelling on a pitch?

The reason I ask is that I've just bought a Dunlop simple assist system like the op, but I also have a spare land rover compressor here, which I'm thinking of using along with a tank and a valve block to allow the rear to level on sloping (within reason) ground

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MikeD

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Out of interest, asking those that have an on board compressor - how well do you find using a rear bag only system manages with levelling on a pitch?

The reason I ask is that I've just bought a Dunlop simple assist system like the op, but I also have a spare land rover compressor here, which I'm thinking of using along with a tank and a valve block to allow the rear to level on sloping (within reason) ground


We use ours occasionally to level the van - the rear will lift about 4 inches in total. Side to side we hardly notice the difference.

We don't carry ramps any more.

But as most of our motorhoming is in Spain we hardly need to alter the van as most pitches are fairly flat anyway.

The air bags are so small a bike hand pump would change the pressures/ride height fairly quickly. I would not pay for another compressor if this one broke. (y)
 
Sep 11, 2020
92
77
Aboyne
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75,732
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Apache 634
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Since 2020
Interesting thread. Any advice on the cost/benefit of adding a semi-air suspension to our 2008 Apache 634 would be welcome. Is it eye wateringly expensive? I ask because I did enquire about adding levelling rams and that was quoted as £5k.

I'm keen to make sensible cost-effective improvements to our vehicle.

d
 

Two on Tour

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Interesting thread. Any advice on the cost/benefit of adding a semi-air suspension to our 2008 Apache 634 would be welcome. Is it eye wateringly expensive? I ask because I did enquire about adding levelling rams and that was quoted as £5k.

I'm keen to make sensible cost-effective improvements to our vehicle.

d


Semi-air suspension and a levelling system are two different things for different purposes, what is it your wanting to improve on you MH ?

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Sep 11, 2020
92
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Aboyne
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Semi-air suspension and a levelling system are two different things for different purposes, what is it your wanting to improve on you MH ?

Yup, I understand that. I was, rather clumsily, illustrating that the hydraulic levelling system was an enhancement too far in terms of cost-benefit.

So, what I'm asking is....

Does semi-air suspension improve the ride and handling sufficiently to justify its cost? Also, is this type of system worth considering?


cheers

d
 
Sep 11, 2020
92
77
Aboyne
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75,732
MH
Apache 634
Exp
Since 2020
Without a doubt semi-air suspension has improved the ride and handling on our MH.
I bought a 2 gauge system with an onboard compressor for not much over £300 and fitted the whole lot in a little over half a day.

Thanks Paul, it sounds like adding this to our vehicle makes a lot of sense. Sensible money and improved handling, what's not to like. Is it the cylinder-less Dunlop system you fitted?

There does seem to be some debate in this thread about the need for a compressor but to me, it would deliver a more user-friendly solution.

d

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Sep 11, 2020
92
77
Aboyne
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Looking on here it's around £750 all in for the kit.


d
 

Two on Tour

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Jun 29, 2012
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Following a question on another forum re semi-air suspension it got me thinking about the way it should be configured on a manual (non-compressor) setup.

I’ve fitted the Dunlop semi-air system without the con board compressor & tank and thus have a gauge with a two-way valve setup where you can isolate each airline to the 2 independent bellows (nearside / offside).

I’m of the opinion that when on the road, I should isolate each side from each other to maintain the pressure in each side.

However, another person has recommended that the valves are left open, effectively having the same air circuit across the two sides (they said that an installer recommend that) meaning that air can move from bellow (side) to the other (side).

But in my view if you leave the valves open then when cornering / turning, then natural movement due to centrifugal effect would roll the vehicle to the outside of the turn, put pressure on the bellow and thus force air into the opposite side, exacerbating the roll effect. In summary making the roll even worse.

What’s your thoughts / how do you setup your suspension?

P.S. Can everyone please refrain from turning this thread into a COVID/Brexit/Scottish Nationalist one. It would be nice to have a thread that sticks to the topic for once.
I know this question has been answered - but I thought this quote from the installation instructions for fitting the guages on the Dunlop system might help.

"After inflating your system, always close the valves (their bold typeface), and only open one at a time when you wish to check the pressures. Keeping the valves closed prevents air passing from one side of the vehicle to the other which can happen when cornering or travelling along roads with an adverse camber"

The instructions go on to say that you can inflate the heaviest side of the van to a higher pressure - if, because of water tanks/furniture etc, one side is heavier than the other.

And it recommends lowering the pressure to 5psi if the vehicle is left for long periods.

This bit of the instructions has implications for when/if you have to change a wheel - "When raising the vehicle, always lift the vehicle by the axle, rather than the body/chassis. If it's necessary to lift it by the body/chassis, release all (see note about AL-KO kits) the air ...to prevent potential damage to them being stretched under pressure" For AL-KO leave about 5 psi - NEVER use the vehicle with no air pressure in the bellows - it will damage them.

P.S. Given the praise for semi assist air suspension from owners - do van converters/MH manufacturers fit them as standard? I've just converted a Ford Transit Tourneo and the body-roll was noticeable the first time I went around a right-hand bend (my furniture is on the passenger side. I've just bought the kit.

P.P.S. the kit comes with a form ( "Manufacturers declaration of European Conformity") which has to be signed by suitably trained personnel and with a company stamp. I was thinking of doing it myself but - Failure to send the form to Dunlop Netherland within two weeks of the installation will render the warranty void.

P.P.P.S. do you still want us to refrain from COVID/Brexit/Scottish Nationalist comments? :giggle:

Cheers

Spike

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Jul 12, 2013
3,035
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The City of Henlow
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26,906
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Adria Supreme
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Since 1980
My Adria came with factory fitted rear air suspension. My previous Dethleffs van, without air suspension, broke its rear plastic corner panel three times by bottoming on first a sleeping policeman in France, then on a steep diversion road in Spain and finally on a hairpin bend in Uzerche in France. Fitted air suspension and never bottomed again.
 
Jun 14, 2014
539
774
Coventry
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31,965
MH
Adria Coral 670 slt
Exp
Since2014
Looking on here it's around £750 all in for the kit.


d
I did mine last year as part of uprating to 3850kg supplied from SV Tech. Cost was about £300. Really easy job to do about half day steady work and a great improvement.
Don't bother with electric pump. not with the trouble as you don't have to change pressure that often also it is independent set up for each side.

Having had the system on for about 9 months I noticed the drivers side was losing pressure slowly but despite bubbling all the joints I could not find any leaks.
Must be the airbag I thought. So I called SV Tech went through everything I'd done and they sent out another air bag within the week no problem excellent service.
Changed the bag replaced the pipework and Schreader valve and still had the leak. Another call and they sent out a new gauge that fixed the problem.
Certainly recommend air bags and SV Tech.
 
May 30, 2020
49
84
Crewe, UK
Funster No
71,221
MH
Dethleffs Trend
We have ours fitted to a compressor, via a relay, full time, with one way valves on each circuit. Travelling, we normally have about 2-bar in each, which is comparable to the original suspension height. At home we are parked fairly flat and use the bellows to level the van for travel. We can raise the rear on the move, for example if we hit a steep slope etc (we have a low tow bar) and drop it down again when on the flat. We also use the bellows to help level the van when parked and find that, at higher pressures, we lose a lot of the rock-and-roll while moving about in the van. All in all, a very good purchase and an easy install.

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Apr 22, 2018
3,080
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We have ours fitted to a compressor, via a relay, full time, with one way valves on each circuit. Travelling, we normally have about 2-bar in each, which is comparable to the original suspension height. At home we are parked fairly flat and use the bellows to level the van for travel. We can raise the rear on the move, for example if we hit a steep slope etc (we have a low tow bar) and drop it down again when on the flat. We also use the bellows to help level the van when parked and find that, at higher pressures, we lose a lot of the rock-and-roll while moving about in the van. All in all, a very good purchase and an easy install.
Agree. I adjust my rear height a lot. Such as at home I drop the pressures right down so the roof has a greater slope to keep the water off.
 
Mar 6, 2021
41
57
Worcestershire
Funster No
79,578
MH
Dreamer D68 PVC
Exp
A little
We have just taken delivery of a Ducato based Dreamer PVC with the heavy chassis option. This came fitted with aux air suspension from Euro Air. There is no guide to using this other than a basic manual which states that min pressure should never be less than 0.5 bar and the difference between the left and right side should never be more than 0.5 bar.

There is no onboard compressor so it's DIY adjustment.

After sitting on our drive for around 2 weeks, I was entering the van and was surprised to hear the suspension complaining loudly. It was creaking loudly as I moved around inside the van as well. I'm no lightweight but I wouldn't have expected this. On checking the aux gauges, I noted that one of them was showing 0 air. I called the dealer to find that they knew as much as me about this system and said that vans had started appearing with these systems fitted a year or two ago.

After chatting to one of the dealer techs, I added air to the low air bag so that it had around 2.3 bar which was the same as the other gauge. Having checked it again the following day, the one gauge had lost air again of around 15% in 18 hours. The dealer now has the van to check for air leaks in the aux system.

Can I check with the knowledgeables on here that I'm correct in my expectation that the system should not be losing air in normal use other than whether you choose to manually release it via one of the valves? I ask because after handing the van over at the dealership and speaking to one of the techs and advising that the right hand side gauge was the one losing air, we were both puzzled to find that the LHS gauge was now the one reading low. They had both lost air overall so my conclusion was that both were leaking.

Can I also ask what layman advice you might have for how to best make use of this system when it's not leaking air?

I've seen posts that say that good results have been achieved from putting about 2.5 bar in the bags. That seems consistent with the level of air that I recall seeing on the gauges when I first picked up the van.

I've seen videos that say you should apply air to whichever side needs it in order to level the van according to the weight distribution. That option 'seems' somewhat limited if the difference between the 2 should never be more than 0.5 bar as stated in the manual. I think the maximum for either side is 5 bar anyway and I guess you wouldn't go that far in any case as this would probably make the suspension very harsh.

The best I can glean so far is that these aux air suspension systems are used to replace the bump stops that are normally fitted to the leaf suspension and that this should improve the ride experience from being very harsh if the loaded van would normally result in the suspension being on the stops for most of the time (and presumably improve the life of the suspension). On that basis, I guess it's trial and error after testing the loaded van out on the road ie if the ride seems harsh, add 0.5 bar and try again and repeat/check for best response?
 
Oct 22, 2019
844
2,679
Hampshire
Funster No
65,995
MH
Chausson 640 welcome
Exp
Since October 2019
I may have missed it on the long stream of replies but I find the on board compressor handy as it also enables me to make minor level adjustments front to back and side to side if the ramps are not enough . And simply inflate when I drive off

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