Could i ask a very basic question ?
Could someone explain the lever normally situated at
the back of a trailer that adjusts the rear ride height of
the trailer.
I know this is to do with the trailer height when going onto
a bay but would like to understand it more.
Or have i got it about right.
Most work the same way, in one position normally down it is set for road use. moving the lever forward or back raises or lowers the suspension once at the level required, depending on the system, you then either move the lever into a lock position or it is spring loaded lever that goes back to the down position, but to reset it for road use you pull the lever out, instructions should be on the trailer.
Well, although I am very new to all these air suspended trailers and stuff , my understanding is that its main use is not so much to adjust the height to suit different bays, but to allow the trailers to be pulled, both here, and on the continent. We can run trailers at a higher level than they can in europe, hence the reason why you see a lot of foreign lorrys with smaller than average wheels and lower profile tyres. This lowers the fith wheel height on foreign lorrys, so therefore the trailer has to come down to allow the trailer to run level. We over here in Britain run on standard size wheels and tyres, so our running height is higher, so we pump the suspension up to level out the trailer.
Also, whilst the trailers are in transit, (Not the van!!), ie, on a ferry, all the air in the suspension is dumped, This makes the trailers more stable when they are strapped down to the decks of the ships.
Hope this helps, and if I got anything wrong, I’ll be corrected in due course 
… LOL
Not quite, there is a ride hieght setting on the lever that should be used on the road, not running with the ride hieght set can damage the airbags, although you can pull them with the suspension set to a differant level to get round an obsitcle as I had to to get through the tunnel at Le Mans.
When I pulled tillts you were supposed to dump the air when leaving them on the docks for shipping, we also pulled some of the mega cube trailers and they had differant airline connections for small wheeled untis and standard units, depending on which connection you used would depend on how far the suspension raised.
AndyM, not sure that I would agree with everything you have put there. 
Yes, there is validity in your comment about ferries, and it is true that different Euro countries have different height limits (I believe Switzerland is 4 metres) but we’ll have to wait for someone else to clear that up.
As for running the trailer at different heights, the load-sensing valve, (as I understand it) has two functions. The first is to maintain the correct ride height whatever the load, and the second is to vary the pressure to the trailer brakes according to the weight carried. Mess with the trailer height and the brakes will be unbalanced relative to the brakes on the unit.
I ONLY alter the trailer height for loading/unloading. Most useful when having to load with a pump truck. Raise the trailer and lower the drive axle, and then hopefully, you are always pushing the load downhill.
Work smarter not harder. 
Looks like two of us were posting at the same time. DOH
Krankee:
AndyM, not sure that I would agree with everything you have put there.
Yes, there is validity in your comment about ferries, and it is true that different Euro countries have different height limits (I believe Switzerland is 4 metres) but we’ll have to wait for someone else to clear that up.
I wasnt actually thinking of the overall ride height of the trailers. Is it correct that the euro trucks have a lower fith fheel height than british trucks??.. Ive seen lots of euro trucks running around on smalls wheels with low profile tyres and this lowers the fith wheel height to below a meter… or so it looks…
As for running the trailer at different heights, the load-sensing valve, (as I understand it) has two functions. The first is to maintain the correct ride height whatever the load, and the second is to vary the pressure to the trailer brakes according to the weight carried. Mess with the trailer height and the brakes will be unbalanced relative to the brakes on the unit.
Ahhh, I thought there was something along these lines too… but I couldnt quiet remember what my on the job trainer said… (there was a lot to take it… )
I ONLY alter the trailer height for loading/unloading. Most useful when having to load with a pump truck. Raise the trailer and lower the drive axle, and then hopefully, you are always pushing the load downhill.
Work smarter not harder.
Well luckily, i am never gonna have to do this, as all the trailers that i am pulling are all pre loaded. But its certainly something to think about…
David14:
Could i ask a very basic question ?
To paraphrase something that has been stated on these forums many times.
The only dumb question is the one you never asked. 
And as you can see David… Its not such a ‘Basic Question’ after all…
AndyM:
I wasnt actually thinking of the overall ride height of the trailers. Is it correct that the euro trucks have a lower fith fheel height than british trucks??.. Ive seen lots of euro trucks running around on smalls wheels with low profile tyres and this lowers the fith wheel height to below a meter… or so it looks…
Not sure about that, but I have heard drivers say that it gives better handling. 
Obviously, with low profile tyres the centre of gravity of the unit is lowered, but as I never intend to drive an artic as if it was an ■■■■■■ RS, the difference on that point is academic.
What I have noticed is that, with a topliner (and therefore a higher C of G), on a bumpy road, the cab rocks all over the place. In that situation low profile tyres could make the unit more stable.
As with everthing. There is always a trade off between cost and desireability.
Well luckily, i am never gonna have to do this, as all the trailers that i am pulling are all pre loaded. But its certainly something to think about…
You will. One day, believe me. 
Andy the reason some trucks run on smaller wheels is to allow them to pull the high volume trailers. As you say this is because the bridge heights in Europe are lower than the UK 4.0m in some places, Belguim and Germany I think, so to get the load height to carry a decent volume of low weight cargo you have to get the trailer closer to the ground.
David - In my experience the 3 way valve on the trailer should normally be at the centre position for normal running.
From memory, turn to the left and it releases or ‘dumps’ the air from the trailer air bags,turn to the right and it adds air.
This is a handy tool to help load and un-load your trailer.
When I pulled a low-loader trailer, the air was ‘dumped’, or the trailer lowered to un-load the machine on the trailer.
This had the effect of lowering the trailer some 3 or 4 inches.
If you run loaded with the air valve lowered,you risk your tyres catching on the underside of your trailer.
I have also seen trailer airbags explode because the air valve has been left in the up position.
On fridges and curtainsiders that you have to un-load yourself,raise the air on the unit, lower the air on the trailer,and so long as the dock leveller is in good order your palletts will ‘glide’ off 
Perhaps someone like Coffeholic will be able to shed more light on this.
Cheers,
Niall.
Lifting the axel on your unit and dumping the air out the trailer on a roller deck will help the pallets roll to the back door. A supermarket back door that is on a slope will either mean that you are killing your self trying to push the cages out or the cages are chasing you out of the trailer trying to kill you so you can either heighten or lower the back of your trailer to make it more user friendly. I have also dumped the air to load low loaders as already mentioned and to get a machine under a border line bridge (shhhhh! )I also dump the air when I’m loading horses to lesson the gradient of the ramp and some loading bays vary in height and with trailers varying also it is often worth jacking the air up or dumping it depending on the depot your at.But don’t run with the air dumped because the gaffer gets very exited when you burn nice big holes in his spray suppressers! As you can see there are lots of reasons to get your self used to adjusting the height of your trailer.
AndyM:
Work smarter not harder.
Well luckily, i am never gonna have to do this, as all the trailers that i am pulling are all pre loaded. But its certainly something to think about…
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Don’t bank on it Andy you’ve got a lot of your working life to come and things change.
Oh and I forgot If you drop your trailer on it’s knees like I did last friday then dumping the air makes it easier to pick up.
switzerland is DEFINETLY four metres . i know because rh used to send me regularly with tilts running at 4.12. i know the exact height because they measured and fined me regularly too . (the firm paid-NOT me )
some trls are run on smaller tyres due to the bridge heights in europeon countries,if you don’t level your trl height out to road running height you run the risk of damaging the trl and not to mention ripping off your mud guards ect.some loading bays require that you drop the air out of the bags so as to stop the trl bouncing forward of the bay and also damage to your airbags.for the newbie’s and wannabies out there always ensure your lever is centralised to allow the trl to reach travelling height for road use.don’t get caught out.
I had seen the notice "please dump air " before
putting trailer onto loading bay.
So appreciate all of your comments.
More and more trailers these days are coming so that you can’t run with the air in the wrong position if you forget to reset it after loading. They are OK for shunting round the yard or getting on or off the loading dock but above a certain speed they flick back into running height automatically. We have some like that.
Some places that pre-load your trailer will pump up the suspension as they load the trailer. This is because the of the trailer drops as they fill it up because of the weight of the load. So they pump up the air to keep the trailer level with the bay.
So if you hook up and pull off the bay without checking the lever is in the middle position and the loaders have left the lever in the “up” position - the back end of the trailer will rise up as you are driving - causing damage to the fun errm sorry - air bags and if you have one of them big double decker trailers, possibly rattling it off a motorway bridge.
So think on and look sharp!!
Oh and some of the ferrys to Holland won’t let you on if you are over 4m tall.
Just a little message for Mr. KRANKEE MODERATOR…
Please, please dont use MY signature, ‘Be safe, Work Smart, Not Hard’
I shall become very upset and have a hissing fit and start charging royalties at an exhorbitant rate
Thank you for your rapid attention to this matter…
Ooops, I almost forgot,
‘Have a nice day’