[77newell]

I've got one of those "DOT check valves" between the engine driven compressor and the Brakemaster 60 dryer on my 93 coach. According to what I was able to find on the Bendix site smaller versions of this valve are used to ensure that an upstream pressure is at some pre-established pressure before it lets air flow through. The idea is to prevent air from passing from critical uses to non-critical uses unless sufficient pressure is present. I'm guessing Larry's valve works the same way though in a larger size that I found listed on the Bendix site.

On my coach's valve near the compressor I'm thinking it is used to prevent the turbocharger air feeding the compressor from blowing out the vent when the dryer is bleeding down. Newer dryers have internal valving to prevent this but the earlier model 60 may not. I'm planning on asking Newell about this tomorrow. I'm switching to a Bendix AD-9 dryer like I installed on my 77 coach (which had no dryer when I bought it). After that installation I never found any water or oil in any tank drains and ended up replacing the drains with petcocks that I checked once per year with no worries about air leaking.