New Job, possible issue with Trainer's truck

Your trailer is operating properly. If you look around on the chassis or tank you might find the original sticker that says the rear air bags are deflated once the trailer parking valve is pulled. This is normal operation for when the trailer is dollied. If you lower the landing gear with the air bags inflated and disconnect the air supply to the trailer for parking the landing gear has extra stress applied to it if the airbags deflate. So, to compensate for this the rear air bags are deflated once the red valve is pulled. That way when you drop the landing gear there is not any extra stress applied to the landing gear legs.

To see how this added stress effects the landing gear, pull both parking valves and let the trailer air bags deflate. Then, push the yellow valve in and you will feel the truck start to creep forward. That forward creep is the pressure that is being applied to the landing gear if the airbags deflate after the gear is down.

If you look at the suspension on the trailer and how the trailer axles are mounted to the lower trailing arms you will see how the trailer moves forward while the bags are deflating.

I have 2 trailers that are setup like this from the factory. The Great Dane Freedom flatbed that I am pulling right now has the tank valve setup to exhaust the airbags when the red valve is pulled. It does take a little bit of time to inflate the airbags and refill the trailer tanks once the red valve is pushed in but it shouldn't take several minutes.

On my flatbed the trailer brakes will release within about 15 seconds and they will release just before the airbags start to inflate.

 

My first tanker truck and almost all of the tanker trailers I pulled with it had disc brakes. The "grab" of disc brakes is usually the first thing drivers notice about disc brakes.

Also, on plenty of past trucks I would notice sometimes when I pulled the tractor brake valve to park the trailer valve would pop out also. I would just learn to cover the trailer valve when pulling the tractor valve. If I were in your position I would assume I just need to learn a different habit not that the truck/trailer/trainer are defective. Do you want to win an argument or have a perfect job?

 

Depending on who's 'spec' the trailer was originally built to and thinking that the fertilizer company wasn't the first owner; it was built to keep the landing gear intact AND to provide some pitch to the rear end to promote drainage.

Usually the air bags used have the interior 'dock blocks' to prevent damage.

Early air bag tank were often parked against old phone poles that defined the parking area and this put pressure on the landing lags.

As the air would bleed off the force would 'flip' the sand shoes as the weight shifted.

Do the 'grabby' brake actuations pull to one side or the other?

If it stops in a forward line it may just be the weight distribution as the product moves.

 

Most trailers have like an extra tank for an air-ride suspension. The are all fed from the same source, but there are check valves which isolate the air between systems, which would keep the suspension air from back-flowing into the brake air system. I'd bet that check-valve is either broken or removed. When you dump the air, does the trailer suspension squat down about 6" to 1'?

 

Sounds like the trailer has controls that operate off the air supply, so when you pop the trailer valve you would no longer be supplying air to the trailer. Thats why you would have to hold it in, like on powdertrains.

 

First time you have to crawl under that trailer to beat on the drums with a hammer cause they froze you'll wish you'd listened to your trainer!.. as for thinking your air lines are crossed, I can assure you that's not the case, sounds like they're rubber, not the cheap plastic coil ones, rubber hoses will typically all be black, only colors will be on the glad hands, exactly as you described.... most trailers are set up so that when you set the trailer parking breaks they also empty the tank, dumping the suspension. Unless you are dropping a trailer, or sliding tandems (which you aren't with a tanker) their really isn't a reason to be setting trailer parking brakes that often, your just constantly deflating your suspension and then filling it back up again for no reason. The parking brakes on the tractor are sufficient enough for parking with the trailer attached. you still have service brakes on the trailer while driving, think of the red knob as the air supply to the trailer (which it actually says), the only time you typically want to cut that supply off is when you are unhooking and dropping the trailer. Make sense?

 

Long as you set truck brakes, and you know their adjusted, can’t move it, it’s fine on level ground.
Some trucks set both axles on truck, some only one axle, you’ll have to look at brake chambers to see if both axles are double pods or if one has a double pod and next axle is a single can.

 

The school you went to was probably an old spring ride trailer so it didn’t take as much to get aired back up and release the brakes.