what is this call?

That is a dock support. It supports the trailer body when the trailer brakes are set so the air bags dont completely deflate and get holes chewed in them from the trailer rocking as fork lifts go in and out of the trailer. They flip out when the trailer brakes are released so the airbags can float as the trailer bumps up and down while traveling down the road.

 

Almost every air ride trailer I've ever seen has had them. If they are missing on a trailer that should have them you may go through airbags more frequently if the trailer is ever loaded with the brakes set, as the bags will completely deflate.

 

Without them properly engaged, a heavy forklift will cause the air suspension to go down so far the dock plate can no longer bridge the gap, flap drops and the fork lift can come to an abrupt stop. Dangerous.

 

Thanks for explaining. I have them too and have never known what for. I still am not sure at what point they kick out or what causes them and because when it happens it sounds rather violent, it makes me a little concerned while being under there for brake inspection or adjustment. I just try to remember to stay clear.

Edit. Never mind. I reread your previous post...so they kick out when the brakes are released!
In which case, I know why I was concerned. Sometimes, after a while, when I come to the truck and there is no air in the trailer and when I start the truck and have just enough air to release the trailer brakes but still insufficient amount to release those air bag dock support, I proceed to inspect the trailer and hear that ominous noise. So it is better to remember to hear it first or look and see if they are up already before getting under there.

In other words, a certain danger potential exists when you have right enough pressure to release the brakes - push in the red button and it stays in but those devices may still need more air before they pop out.

 

Anyhow, I am intrigued and will go to the truck earlier at the next task and will make some experiments. It is a shame that I've had this trailer for 5 years and knew about those things to exist but never became interested what they were there for.

So would it be the right conclusion that while at the dock it is better to always set the brakes in order to engage the supports?

 

Theoretically, yes. But there are times I leave trailer brakes released... Such as when it is cold and I'm concerned about freezing brakes. Trying to free frozen brakes on a dock is a #####.

 

I have the tendency to always set them and slide the tandems all the way back. The fact is that for the 5 years I have had the trailer, the air bags are still in a good shape. I'd like to think now that, for the most part, it was the dock supports that did the job.