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My air compressor is very old and has been ‘rebuilt’ a number of times but has now become noisy particularly for the last 20 seconds or so before cut off when, I assume, the back pressure is high and working the bearings etc quite hard. I have just rebuilt the valve block and there are no leaks in the system - it will not drop at all if left on any height setting when parked up for days. It rise and falls as expected when running, does not ‘dance’ when at a standstill, levels it self when parked and holds station nicely. NanoCom reports no faults and all height sensor readings appear OK.

However, due to the compressor being noisy I have become aware of when it operates and shuts off in normal driving and when travelling at a constant height i.e. when not having to transit between ‘normal’ and ‘motorway’ modes, the compressor operates regularly (every one or two minutes) for very short periods of time for between 10 & 20 seconds as if it is just topping up a very small drop in tank pressure. Is this normal behaviour/duty cycle?

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Hi Gavin. There are better EAS guys here than me, but I don’t think the compressor should come on every couple of minutes. I think it indicates a leak somewhere other than the air spring side of the system. And it shouldn’t labour that much. I have a spare pump from a parts vehicle that does that (which I intend to sort out some day), but the installed pump is quite quiet.

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Regarding leaks other than the air spring side of things I should add that if the vehicle is left parked for days on end then as well as there being no discernible ‘sag’ of the suspension it will also rise to normal height as expected immediately on being driven. I would expect any leak from the ‘other side’ of the system to deplete the air tank/reservoir and cause delays to the suspension rising to normal height when moving off from a parked position - I’ve certainly experienced that in the past.

Although the compressor sounds like it is labouring it still has plenty of puff and the noise it almost certainly due to some wear in the compressor coupled with the anti-vibration mounts being past their best. I will change the mounts which will probably quieten things down such that the noise/vibrations are not obvious in normal driving. I think I’m only now aware of the compressor being on because of the noise/vibration and it could well have been doing its on/off cycle for a long time!

I’m just wondering if slight leaks happen when on the move as a normal result of the increased pressure in the air bags as they soak up the bumps and the compressor cycling is normal or, perhaps, my pressure switch has too close a pressure difference between switching off and back on. Or some other reason.

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My EAS pump runs more than 50% of the time. I suspect the leak is the NRV for the rear airbags but seeing as there are no replacements I'm a bit stuck. The back sags over a couple of days when the car is parked, and it takes a couple of minutes to get back to normal afterwards.

When I refurbed the valve block I combined the best NRVs from two sets but one was definitely looking second best even with a new o ring.
FWIW, I just replaced the compressor - the old one lasted 4 years.

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4 years sounds horrible. I’m sure mine is the original 25 year old one (with new seals)

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Oh it'll get new seals and go on the shelf ready for next time.
In the meantime, we need to find someone who can machine new NRV valves. At some point we'll all be sagging overnight ;)

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Agreed! I took apart 3 Valve Blocks to get 3 good NRV’s. It’s only a matter of time…

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'tis odd.

My Valveblock at 130k was original never rebuilt and the only item that needed attention was the diaphragm.

everything else was like new, odd.

I wonder what causes excessive NRV wear in some blocks.

I know a chap on LandyZone that I believe has replacements if anyone is interested.

https://www.landyzone.co.uk/members/kurtjohnson10.95668/

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Update : Having gone through the EAS system with a fine toothcomb I cannot find any leaks and if there is one it can only occur when on the move so almost impossible to find. I cannot find enough detailed information about the frequency the ECU actually monitors the height sensors when on the move and makes adjustments so trying to ascertain what is a reasonable duty cycle for the compressor has also defeated me. The only information for the compressor running are the pressures that it cuts in and out at. Therefore I think it reasonable to assume that the system must regularly monitor the suspension geometry and correct it as necessary when on the move - after all in a leaking system it will 'dance' when stationary with the engine running! It follows that with suspension movement then the readings on the height sensors will continually adjust and the system will try to correct by allowing air in and out of the air springs when on the move and, thus, the pressure in the system will drop and the compressor turned on to replace the used air. In other words the few seconds running of the compressor at intervals when on the move is probably quite normal.

I have also ascertained that there is nothing amiss with the compressor - it just vibrates more when the going get a bit tougher at higher back pressure which is to be expected. I also ascertained that the reason it sounds more noisy since I recently rebuilt the valve block is that, and I'm a bit embarrassed to admit this, I put the domed washers back in the wrong way round! I have removed/replaced the compressor many times and never got it wrong before. Now it's installed properly I can't tell when its running.

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If there are no leaks above a certain speed "5mph" rings a bell the EAS should be dormant and not adjust when on the move..

The compressor should only run on the move if it is trying to compensate for a leak in the system, mine used to when the diapragm was worn and allowing the storage tank to leak out the exhaust.

When I'm driving the compressor never kicks on, until I stop and she levels the front.

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I think the EAS wakes up and resets itself every so often when driving, maybe every 15 or 20 minutes?

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If the system has achieved its required height and all valves are closed then if a leak occurs at an air bag on the move above 5mph then how does the system try and adjust? There should be no loss of pressure in the reservoir once refilled or in the valve block. The only signal to the ECU will be from the relevant height sensor and I’m sure the system will try and adjust! If this is the case then why will it not try and adjust with normal suspension movement?

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From another thread I have gleaned that the compressor is rated for a 15% duty cycle which equates to 9 mins total running time per hour.

I am told that the pump only runs when ‘on the move’ the pressure switch detects a drop in pressure i.e. when there is a change of height requested or when there is a leak on the reservoir’s side of things. Now I know this can’t be the case because when previously I had a minor but definite leak on the air tube to the NSF air bag the system would try and keep that air bag inflated whilst travelling 100’s of miles on motorways without the speed dropping significantly. The only way it could do this was if the height sensor told the system that that corner was drooping slightly.

Now when my compressor was incorrectly mounted (my fault) it was very obvious when it ran due to the vibrations and noise. The obvious vibrations were only very noticeable during last few seconds of ‘top up’ when back pressure was high. I noticed that the compressor would run for a few seconds only and mostly (but not always) when I applied the brakes. I now believe this was due to the front suspension compressing, the height sensor providing the reduced height reading and the system operating to counteract the movement. Hard cornering would have the same effect. Once rebounded the system would be too high and air allowed out to bring the suspension back within limits. This continual operation would result in the reservoir pressure inexorably dropping over time and the compressor running to replenish the reservoir tank.

It was also noticeable that on a motorway/A road drive the compressor would seldom run giving further credence to this continual compensation when on the move. Does anyone know definitely how the system works on the move and if my assumption is wide of the mark?

Furthermore, there are no leaks when the vehicle is parked up for days as the ride height is rock steady with no sagging and when moving off the suspension goes quickly up to normal height. I do not have a pressure gauge fitted so cannot swear to absolutely no leak on the reservoir side but I would think after a week stood standing with even a small leak it might struggle a little bit to get up to normal ride height.

Does anyone know how long an in spec compressor should take/run (mine is in rude health) between the two operating limits of the pressure switch? From my rough estimation the compressor would run in town driving (frequent braking) for a total time of much less that 9 mins an hour. Now I have corrected the compressor mounting I can’t really detect when it’s running when on the move so can’t measure its overall running time.

However, having said all that I have the feeling that the on/off limits on my pressure switch may be a bit too close together resulting in the compressor switching on too often (albeit for short durations) and without fitting a pressure gauge the only other way to do a rough test is by timing it’s running period.

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I suspect there must be some hysteresis in the ECU so it doesn't try to correct constantly while being driven. Think about it, if you are in traffic and put the brakes on, the front will drop as the suspension compresses. If it immediately opened the valves to put more air in to level it, as soon as you come off the brakes, or accelerate away (so the front lifts), it will then be opening the valves again to drop the height but then it would be too low when you achieve constant speed, and hence height, again. That all leads me to think there is a delay between it seeing a change of height and correcting it to allow for normal driving.

Incidentally, if it doesn't drop when left for days, why would it need to immediately rise to Standard height? Surely, unless it is dropping, it will still be at Standard when you restart it so shouldn't need to rise?

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Mrs Garvin has short legs - so it is always parked in access mode! It rises to normal height within a few seconds of driving off.

I agree that I would expect some delay in the ECU to stop the system correcting when it’s not strictly necessary but to cater for a ‘flying carpet’ ride without excessive dive/squat under braking/acceleration the delay might be quite short. I also think the pressure switch may also be a bit too ‘keen’ in its operation, kicking in with very (too) little loss of pressure in the reservoir tank.

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Had a thought after posting my last, all EAS movement is inhibited when the brakes are on (for the first 3 minutes anyway), so it isn't going to do anything under braking. I tend to leave it in D when stationary and have noticed that after 3 minute delay of sitting in traffic and not moving, it will suddenly wake up and adjust the front but not before then.

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It’s a right old malarkey trying to piece together the algorithms that swim about inside that EAS ECU! Back to the first question - so why does my compressor run so often for such short periods of time when there is no evidence of any leaks?

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As you suspect, it might be that the pressure switch is a bit keen, it should be open at under 120 psi and close at 140 psi. I've just acquired a number of valve blocks and intend making up a test rig so I can rebuild them with new O rings and diaphragm, check the driver packs for correct operation and leak test them. It won't take a lot to check the on/off pressures on the pressure switch while I'm at it.