Hello All. Feel a bit silly asking this.but is there any reason why the airbags on a trailer won’t inflate? We had a trailer sitting for the last 2 months and when I went to move it in the yard the suspension lever at the back of the trailer had no effect. There was no sound of rushing air either so it doesn’t seem like a hole in the lunes or bag.It is probably something really stupid I have forgotten to do but i can’t think what it might be.
Was the trailer suspension adjusting valve stuck out or in depending on its type, some you have to pull out for them to level, some you put back to centre position and a spring inside should push the handle out to re-levelling position, all types can get a bit sticky/seize if not used often.
If the trailer has completely drained and you’ve got a small compressor it can take a long time, up to ten mins on fast idle, to fully inflate a 3 axle trailer, if its one of those stub axle super low independent sprung double deckers or glass carriers with stub axles it can take an age to inflate.
Course it might just be knackered 
The bags only inflate slowly to begin with from empty tanks so if the leak is large enough you won’t hear it. An empty trailer may only require about 14 psi anyway. Or maybe one of the levelling valve linkage rubbers could have broken, leaving the valve set on dump air.
What could be worth considering, block the air pipes off to the airbags until the tanks are full enough to release the brakes, then un block them one at a time, if there’s a leak you’ll hear it then.
You can kink the lines over and run a cable tie around some cardboard or something around them (cardboard or similar to use to prevent cable tie cutting through the airline)
daesal:
Hello All. Feel a bit silly asking this.but is there any reason why the airbags on a trailer won’t inflate? We had a trailer sitting for the last 2 months and when I went to move it in the yard the suspension lever at the back of the trailer had no effect. There was no sound of rushing air either so it doesn’t seem like a hole in the lunes or bag.It is probably something really stupid I have forgotten to do but i can’t think what it might be.
Have you connected a tractor unit to it, connected the air lines and let the engine run on the truck to build up the air? If it’s been stood for 2 months then it’s probably completely out of air which is why the trailer suspension lever isn’t doing anything. What do the air reservoir dials show on the truck dashboard and do they climb when you rev the truck? If they’re not moving at all and you have the air lines connected then you’ve got a major leak somewhere, but you’d be able to hear the air leaking out for that volume of air.
waynedl:
What could be worth considering, block the air pipes off to the airbags until the tanks are full enough to release the brakes, then un block them one at a time, if there’s a leak you’ll hear it then.
You can kink the lines over and run a cable tie around some cardboard or something around them (cardboard or similar to use to prevent cable tie cutting through the airline)
easier to put the valve in hold position until the unit shows full air then remove the pipes which feed the air bags from the valve .waynedl since when will a cable tie cut through an air pipe ? The pipes kinked over on an older trailer are more likely to just snap .
what sort of trailer is it ■■
when i used to steer a wagon, we had 30 foot lift tank skelly trailer’s, and to drop the suspension to get a better angle to discharge all the product we either pulled the red air airline which a. applied the trailer brakes and b. dropped the suspension
or
on the older trailers there was a separate button/knob which you pulled to drop the suspension, again to get the angle
but some muppets didn’t push the button back in before setting off… the smoke coming off the trailer mudwings being worn away by the wheels was a sight to see… 
check for this other button
Thanks for all the replies.Definatly food for thought there.sorry I didn’t reply earlier I’m just back in.The trailer is a Concept Urban Curtainside. The air gauge in the cab was reading about right. I checked to see if air was going into the brake tanks on the trailer by using the red manual release/on on the trailer chasis and there was definatly air coming out. It is a single axle trailer so I was thinking it shouldn’t take too long to inflate.
daesal:
Thanks for all the replies.Definatly food for thought there.sorry I didn’t reply earlier I’m just back in.The trailer is a Concept Urban Curtainside. The air gauge in the cab was reading about right. I checked to see if air was going into the brake tanks on the trailer by using the red manual release/on on the trailer chasis and there was definatly air coming out. It is a single axle trailer so I was thinking it shouldn’t take too long to inflate.
Are the brakes sezied on or will it move if if you try (the trailer)?
Sounds like the differential pressure valve has stuck.
The trailer brake tank has to reach 9 bar before it starts to supply the suspension tank.
The brakes are a protected circuit.The idea is that air is fed to the brake tank first,on the brake tank is a check valve set to 9 bar,once the air reaches this pressure the valve opens and supplies the suspension tank.
This stops the brakes loosing spring brake pressure and always having enough air to apply the foundation brakes and keep the emergency relay valve open if one or more air bags burst.
If you look on the air tanks you will see a valve on either the outlet side of the brake tank(usually the larger one) or the inlet side to the suspension tank.This has a none return spring and diaphragm inside.If they are stood for awhile the diaphragm sticks and stops the suspension tank filling with air.
Same thing happens on rear air bags on tractor units.
Brakes seem to be working.
That diff pressure valve sounds likely.
Is there a way to test/release it?
I will try go up the yard today and have a look.
If the valve is on the output side of the brake tank disconnect the outlet pipe and build pressure.At about 8 or 9 bar you should feel air coming out.If its on the suspension tank unscrew the valve and check for supply into the tank.
As the valve acts as a buffer dont expect a big rush of air as it is only leeching off the brake circuit.
If the air bag ring circuit is leaking or a bag has burst you wont really hear it as the suspension circuit only fills slowly.
Air is fed from the tank to the lift/lower valve first then to the ride height valve.This is so that the lift/lower valve can over ride the ride height valve when you pull the lever out.Maybe check you got a feed and out put from the lift/lower valve if the suspension tank is charging.
Sorry didnt see that it was only a single axle trailer.This may only have one air tank due to reduced air requirement but will still have a protection valve on the tank to keep brake pressure at operating pressure in event of a burst bag.
Some newer trailers have 2 tanks but each tank supplies the brakes and suspension on the near side or off side of the vehicle.Each side is independant of the other and there is no air bag ring feed to all the bags.
daesal:
Brakes seem to be working.
That diff pressure valve sounds likely.
Is there a way to test/release it?
I will try go up the yard today and have a look.
I would go up the yard to see if i could find a fully qualified hgv mechanic who knows what to look for…
meanwhile i would be making us both a brew…
You shall have a Valve on bottom of airtank to drain Water. shall be well pressurised.
You shall have one or two regulations Valve connected to Axle.
Think just one and rubber-connector faulty perhaps. If Rubber is straight and not cut,well,…
You could nick a Empty Spray Bottle from Wife,put a 1/8 Liquid Soap or Shampoo in it,filling up with Water and spray it the Airpipes along and around Air Bag. If you see Booble its a Airleak. If many Booble its a bad airleak,but it shall get you somewhere closer to a fix.
Thanks for the help and encouragement. All fix ed. Was a sticky valve so now all trailers have been done too.