Foretravel Owners' Forum For owners and Fans of Foretravel Motorcoaches September 06, 2025 ...

...so the gauges on the dash are reading the two front tanks...

Thanks Chuck, I understand now, so the gauges on the dash are reading the two front tanks then

Yes.  Verify that the check valves have not failed:
Open the drain by the left rear wheel and remove all air from the wet tank. 
Close the valve.
Half hour or so later, re-open the drain valve.  If any air comes out, one or both check valves have failed.

Steve, you may give those a bit of heat ( just slightly warm)with a small touch or heat gun the spray them. Also a little TAP with a hammer in the CCW direction may also help.

...2 big ones are soaking in power blaster, they dont even want to budge...

Don't be discouraged - just keep working on them and they will eventually let loose.  It took my longest wrench, augmented by a 2' cheater pipe and my total body weight (160# soaking wet), to break them the first time.  I think mine were installed by a 500 pound gorilla on steroids!

When you finally get around to reinstalling the fittings on the new dryer, do yourself a favor and put a dab of "anti-sieze" on the threads.  You'll be glad you did on the next R&R.

Permatex Anti Seize Lubricant 0.1 oz. - Ace Hardware

Thanks Mike J, are you taking about the pressure in the tanks?  mine was about 110 -115 psi on the old one.

Our "defective" rebuilt ones had wrong popoff/safety release valve on them. Shop doing work didn't catch it. Apprently Cummins knows this issue exists on rebuilt units but didn't tell us until we asked. I recall some talk here or on Bealalarm about it. FT uses a higher psi than usual. Not sure about NAPA ones.

This isn't the psi in the tanks. It is only the air dryer safety popoff. Once system reaches max pressure. Cutoff at 130psi

I think there might some confusion about the terminology here. The purge valve on the air dryer is part of the normal cycle of the compressor being unloaded when the D2 governor reaches its set point, it causes the purge valve to open which is what you hear when the set PSI is reached. The pop off valve on the wet tank (normally 150 PSI) shouldn't release unless there is some problem with the governor or purge valve. It is there to keep the tanks and other parts of the air system from rupturing and to protect the compressor. At any rate, it is the D2 governor that that maintains the air system at the appropriate safe pressure to operate the air brakes, suspension, etc. Some people like to set the governors a little higher, say between 110 psi and 130 psi (usual range of 20 psi between cut off and cut in). The ones I have bought from Freightliner or Napa have been preset at 105 to 125 psi.
At least, that is my experience and understanding of the system (and I am always seeking to learn more about how these complex systems interact).
Don

Did you follow reply number 5 and get an isolation valve,sounds like that may be what your talking about.The D-2 valve is located
near the engine air compressor and no where near the air drier and the air drier does not come with a D-2 valve.If the "tech" is at
the coach when he asks about the unloader ask him what he's talking about,no way any of us can tell.

Did you follow reply number 5 and get an isolation valve,sounds like that may be what your talking about.The D-2 valve is located
near the engine air compressor and no where near the air drier and the air drier does not come with a D-2 valve.If the "tech" is at
the coach when he asks about the unloader ask him what he's talking about,no way any of us can tell.

Hi Don. From your description it seems that the D2 valve came installed with the rebuilt air dryers we had installed? Our air purging problems under acceleration ceased once we reinstalled the OEM dryer that came with our coach. Both rebuilt units we had tried purged air at a lower psi that what should have been. When engine rpm ramped up and compressor speed increased during acceleration the dryer would purge continuously for 10-20 seconds. I too am in search of a better understanding of these systems.

Iv'e had a tech use the term "load and unloader" valve on the air compressor. Is this the D2? If so why would replacing new dryer rebuilt units with our old OEM fix the low psi purging? Must be something internal bad on our two rebuilt units? I just want Steve to get correct dryer for his coach and not a bad unit or one that wasn't built to FT psi specs. Maybe my experience is we just got unlucky twice...

Is there a pressure relief dedicated to/and installed in the air dryer?

Mike,
The dryer has a relief valve screwed in the bottom of the unit.
There is a pressure relief valve screwed in the wet tank also.
The isolation valve don't bleed air out to atmosphere.

Pamela & Mike

Word I got was the pressure relief valve on the dryer wasn't rated for the higher psi that FT required. Cummins guy tipped us off that this so called "pressure relief" valve is often not correct on rebuilt units. Wish I had more info than that.

This from service tech email: "Michael, The rattling noise may be the compressor loading and unloading. I know that on Cummins the compressor makes a bit of noise when it is loaded up. It is normal to a point. If it starts sounding like a loud engine knocking noise that would concern me. That would tell me the compressor is not feeling well. The unloader valve may need serviced, That would be something I would have a certified Cummins Repair shop do. They get carbon build up and sometimes causes them to make noise and stick."