Emergancy air hook up.

[wilco]

What dose the emegancy air hook up do when it is hooked up to a military trailor?
Is this only aplicable to trailors with straight air brakes?
My M332 is air activated hydro..

 

[rosco]

Question is a little vague, but if your refering to the Emergency line on the truck, when hooked to a trailer (w/air brakes), it merely supplies air to its system. If the air pressure in that line is cut off, with the Tractor Protection Valve, or by accident, the trailers Relay/Emergency Valve, will set the trailers brakes. On early trailers, those brakes are applied & held on with air from the supply tanks. If the trailer was built after the 151 Safety Standard with "spring brakes", the air will be dropped, that is holding the springs OFF, and the springs will apply the brakes.

Lee in Alaska

 

[wilco]

I thought that might be the case. What dose it do on a M332 Ammo trailor with Air over hydro brakes?

 

[ida34]

The air activates the master cylinder taking the place of your foot on a regular vehicle. The air pressure activates when you push on the brakes in the truck. The air pressure pushes the master cylinder on the trailer which transfers the air pressure to hydraulic pressure that activates the brakes. On trailers with an emergency connection, the trailer has a relay valve and air tank that the other trailers do not. The emergency air is on all the time. If fills the tank on the trailer through the relay valve. When the relay valve does not sense air pressure from the emergency line on the truck it uses the air in the trailer tank to activate the brakes as a break away feature. The air pressure activates the master cylinder the same as on a trailer without the emergency connection.

 

[wilco]

Thanks, thaught that was the case. So itf the trailor dose not have an air tank the emergancy system is not used....

 

[m16ty]

Yes, you're right. Some trailers just have the service line. When you hit the brakes the service air activates the brakes on the trailer. The emergency line isn't hooked up.

I never understood why the Military didn't make the trailers with straight air brakes. Less complicated and less upkeep.

 

[rmgill]

I think the lack of spring brakes is due to NOT wanting an air line failure to stop a truck/trailer combination.

 

[rosco]

Air brakes are bulky and cumbersome. At least the air chambers are. With Juice brakes, the brake mechanisms are tucked away behind smooth backing plates. Air chambers would hang out on one side or the other, of the axles. I would not be so concerned about the air lines, as much as I would be about knocking off the brake pots, in rough going.

Lee in Alaska