Always something to do on these trucks...

[montaillou]

Driving on the freeway today when the low air warning buzzer comes on. Pull onto an exit ramp (that's on a slope) within probably 100 yards, all the while slowing down. As I come to a stop I got both feet on the brakes because I've lost pressure.

But one tank was still fine, at just under 120 psi - the tank on the driver's side. After checking the cable pull valves it seems that one wasn't releasing properly - the one on the passenger's side. Jiggled it, kept an eye on it and got back on the road. Fortunately my trips were short today.

Can someone tell me what's the purpose of two tanks, are they just redundant to each other? Because with 1 tank still at max pressure and the other tank around 40 it really felt like I had very little air at all. I have read about different tanks for different functions on long haul trucks, is it the same on the deuce? The diagram I found on the air system looks like the two tanks are connected.



I'm replacing the valve that appears defective.

 

[jasonjc]

I "think" (may be wrong) the first tank is the "wet tank" the water will settle here and that helps keep it out of the rest of the system. There should be a check valve to keep the air in the 2nd tank from going back to the first tank.

 

[cattlerepairman]

Jasonjc has it correct. The first air tank receives the fresh compressed air and its only other connection is to the second air tank. The problem montaillou was facing was that the air did not go from the driver side to the passenger side air tank, therefore he had no air support for the hydraulic brakes. The air pack is supported from the second tank only.
It is possible for the check valve to fail "open" i.e. allow both tanks to balance and air can go either direction, or the valve can fail closed (gunked up) and no air flows, either way. It should be an easy fix, maybe just needs cleaning.