This might be a simple question of something I’ve overlooked . 40’ tri-axle trailer . Once hitched up the suspension bags fill to what seems the correct ride height , put the lever into drive position ,but then they keep filling! So that after 200m the gap between the mudguards and the trailer is easily 9". And the bags look like cows udders before milking. I can release the air from the lever but they fill straight away once the lorry is driven. Am I missing something obvious? Thanks
My guess would be that the weight sensing valve has failed.
Hard to say.
You are pulling the handle out right? 
I agree with Harry. Most modern trailers default to ride height as soon as you go above like 5mph without even touching the handle.
Look on the middle axle, sounds like the suspension ride height rod assembly has become disconnected, could well be one of the rubber eyes split
Thanks for the quick replies .
Handle pulled out-it also comes out above 16kph.
I will look at the ride height rod assembly today . Fingers crossed.
Your own vehicle or a company vehicle? if it is a Company vehicle just defect it and don’t load it.
4 possibilites spring to mind: faulty levelling valve or jammed/displaced linkage, faulty ride height valve, kinked pipe, electrical fault in Colas system.
Sometimes if you totally deflate if then pull the handle out to road setting it sometimes fixes it
Yes Moose, it is rod assembly. Good call.One of the connectors has given way.
Thanks for all the quick answers.Good to know about that fully deflate fix too.
Just changed rubber on ride height assembly arm. But no luck . The same symptons keep happening. Is there a way to tell what the correct settings are?
Yes but it is too dangerous for your safety to tell you since you will need to be underneath the trailer to do it. Take it to someone who knows what they are doing and will carry out the necessary precautions. This system can kill.
Thanks Cav. That makes a lot of sense! We came to the same conclusion!