Compressor Check Valve

Fredward · April 21, 2008, 05:45:35 PM

On a standard 8V71 with Bendix compressor and governor, where is the check valve? When the governor unloads the compressor head and it stops pumping, what holds the air pressure in the system? I don't see a check valve. I don't currently have an air dryer (although I'm thinking of installing one) The bus is an MC-5A
Fred

Melbo · April 21, 2008, 05:49:02 PM

On my MC8 the check valve was on the firewall almost dead center above the transmission.

It was right after the big flex pipe that connected to the compressor

HTH

Melbo

buswarrior · April 21, 2008, 07:08:51 PM

The purge valve in an air dryer also closes off the line when it purges.

Can't air up the bus, and no air leak to draw you to it, if the purge valve freezes open.

More check valves deeper in the system too.

happy coahing!
buswarrior

Fredward · April 21, 2008, 08:45:15 PM

By the way, I have no air dryer. Just the one that is in line right after the flex hose. It has a petcock on the bottom and thats all. What kind of air dryer should I install? Bendix AD-4?

Stan · April 22, 2008, 05:07:14 AM

IIRC the check valve on a 5A is on the end of the compressor discharge line. Original was large, about 2" x 5", with 3/4" female pipe threads on each end.

niles500 · April 22, 2008, 02:26:02 PM

Fred - most are recommending the AD-9 - FWIW

Stan · April 22, 2008, 05:23:58 PM

Fred: As you well aware, your 5A has run without a dryer for close to fifty years so it isn't a real necessity. As long as you drain your wet tank (the one at the back of the bus) regularly, you won't have a problem. To make the draining easy, you can put a pull type valve on the drain, with a light chain over to the wheel well. Just give it a pull every night when you park the bus.

Fredward · April 22, 2008, 07:29:30 PM

Stan,
Actually when I bought the bus I put a drain valve with a cable on it for the wet tank. Also on both front tanks. One of them (I don't remember which one) had about a quart of water in it. So now I also drain the curb side tank regularly as well. The device at the end of the flex hose coming from the compressor has a petcock on it and there is often water there as well. It appears that the wet tank had some type of automatic water purging device on it that is still there probably just gunked up. Can't figure out how that was exactly supposed to work.

I just like the sound of an automatic air dryer. Had a dream about one being installed in my -5. What a geek.

Fred

Stan · April 23, 2008, 05:08:23 AM

Fred: The little tank with the petcock is primarily an oil separator. If you keep the wet tank drained, you should get almost no carry over into the dry tanks at the front. I used to service my bus once a year and even after 25 k miles of driving there would be no water in the dry tanks.
You are probably lucky your automatic air drain is stuck shut. They usually don't seat and then leak.

buswarrior · April 23, 2008, 08:53:34 PM

Hello.

Automatic drain valves are not well respected devices.

They are prone to nonfunctional behaviour, and as noted, another place for leaks if they get the gunk in them the wrong way. They are also another thing to freeze/maintain in the colder climates.

Manual drains let you see what is going on, work every time and you want to know what comes out!

happy coaching!
buswarrior