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Air brake systems and diagnostics

doublewide

doublewide

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Joined
May 31, 2015
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844
Location
MA
And this one, in particular at about the 7:40 minute mark;



The narrator is describing what happens during a trailer breakaway or trailer supply line failure. He states that the Trailer Air Supply Valve will shut off trailer supply air because the air is escaping faster than it can be replaced. So this goes back to my question in post #75 ;

doublewide said:
View attachment 227945 My manual shows 3/8" air line for the TC valve which seems fine, But you'd think the PP-7 valve would need a larger line. The air supply for the trailer has to come all the way from the tank, up into the cab through the valve and then back out to the TP valve and then to the trailer?
Click to expand...

Based on the video, it appears that the 3/8” supply line is undersized intentionally to create this imbalance in the valve that results in the airflow being shut off and therefore retaining air in the truck system.
 
Truck Shop

Truck Shop

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Dec 7, 2015
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16,898
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WWW.
That's correct plus on long trailer set ups there is a thing called a speeder valve slang term. To speed up service brake delivery. Sealco is the main maker of that valve right along with
most trailer valves.
 
doublewide

doublewide

Senior Member
Joined
May 31, 2015
Messages
844
Location
MA
The other day when I was adding the T’s I noticed that a couple of the original air lines had chafed against the frame and worn through the outside color and were showing the white under layer.196394CF-4AB6-4183-875C-8332EAA6AF45.jpeg
 
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