Airing up, but not purging..

NewbeeMC9 · May 09, 2018, 09:33:21 AM

Got the PPV replaced...
Replaced purge valve ( AD-9)

Bus is airing up but not purging, probably hitting the relief around 125-130 and kinda staying there...

Do I need a new governor and or Compressor? Change the the dessicant? Will run the time test this weekend...

Thanks in advance...

Lee Bradley · May 09, 2018, 11:31:21 AM

Probably time for complete service of your air dryer.

Oonrahnjay · May 09, 2018, 12:58:05 PM

Quote from: NewbeeMC9 on May 09, 2018, 09:33:21 AMBus is airing up but not purging, probably hitting the relief around 125-130 and kinda staying there...

That sounds to me like the governor is working fine, but they're so cheap that I'd put a new one on if my bus was having a compressor or air dryer problem (*my* opinion, only). But the big issue sounds like dryer.

NewbeeMC9 · May 09, 2018, 03:48:00 PM

Put a new purge valve/ heater, and have new cartridge to put in, will do that next now that it's a little easier to move and get under... Anything else I may be missing?

kyle4501 · May 09, 2018, 05:33:48 PM

Quote from: NewbeeMC9 on May 09, 2018, 03:48:00 PM
... Anything else I may be missing?

Yes, but not enough space to list it all . . . .

NewbeeMC9 · May 10, 2018, 02:05:51 AM

Yep, not just another thread, but a whole nother forum....

buswarrior · May 10, 2018, 07:21:11 AM

The signal lines to the purge valve are present, and connected at both ends?

Governor activates the air drier purge valve via a pneumatic signal.

Add-on air driers may have this important step missing. Yes, believe it or not, there have been busnuts who knew enough to install the drier, but didn't know enough to install the signal line...

Happy coaching!
Buswarrior

chessie4905 · May 10, 2018, 10:15:05 AM

That happened on our 4104. About 6 months after installation by someone else, nylon hose blew off connector and about a qt of water came out. Reattached line and tightened more. Then checked signal line at governor on air compressor. It was connected to wrong port on governor. Corrected that and it started purging and working normal. Had wondered why you didn't hear it purge before, but wasn't familiar with air dryers.

Here's a picture with port placement.

https://www.google.com/search?q=bendix+air+compressor+governor&oq=bendix+air+compressor+governor&aqs=chrome..69i57j0l3.17727j0j4&sourceid=silk&ie=UTF-8#imgrc=Vu-S2y5mMOrbuM:

NewbeeMC9 · May 10, 2018, 10:54:09 AM

That is a good point BW, this one was installed by professional bus mechanics and has worked for many years, it did sit for a few years and started doing this on the way to the great white NE, lol...

bevans6 · May 10, 2018, 11:20:55 AM

One thing you can try... Crack the air line to the purge valve and see if there is air pressure there when the valve should be purging. The governor is kind of like an on/off switch for air. It has a sense port and a signal port. The sense port is connected to the air system downstream of the PPV, and simply monitors the air pressure in the system. Once the air pressure in the system reaches it's high set point the governor switches from off to on. When it switches on it sends full system air pressure out its signal ports. One port is connected to the compressor (usually the governor is bolted directly onto the compressor head so this port connection is direct, with a gasket for sealing) to tell the compressor to stop compressing and the other port is connected to the purge valve on the air dryer. As long as the governor is sensing system air pressure higher than it's low set point (usually 95 PSI) it stays on and the air pressure holds the purge valve open. So if you get things so that the air pressure is building up to the high set point (125 psi) and crack open the signal line on the air dryer purge valve, once air pressure causes the governor to switch you'll hear air escaping from the cracked line at the purge valve. If you don't hear air, something is wrong with the governor, the connections or the signal line. If you do hear air, the purge valve is bad. The governor has several sets of ports with different holes, some of them plugged. It also has a black or blue plastic cap on one the that covers the adjustment mechanism. The sense ports are the ones on the other end of the governor farthest from the cap, the signal ports are in the middle (between the two holes for the bolts that attach it to the compressor, and there is an exhaust port pointing down nearest to the plastic cap. The exhaust port needs to be open so air can come out and needs to be pointing down.

Brian

Lee Bradley · May 10, 2018, 12:27:13 PM

Sounds like your governor is working; stops the compressor at 125 to 130 little high but OK. Relief valve should be up around 150 psi and you should hear that. Governor works by applying air, at set point, to
pistons in, the compressor, that lift the spring loaded valve on each compressor piston and the air travels back and forth between the cylinders. That air signal should also be applied to the purge valve. As others
have said, sounds like the signal is not getting to the purge valve; wrong/plugged governor port, failed signal hose, etc. If you have shop air, you could try applying that to the purge valve signal port to see if the
purge valve works.

buswarrior · May 10, 2018, 12:38:22 PM

An FYI, the new equipment is often running at higher pressures. 130 is not unusual.

Depending on your vintageand beliefs, busnuts may want to make some adjustments once a new governor has been installed.

Happy coaching!
Buswarrior

Jim Eh. · May 10, 2018, 05:54:58 PM

I often find the adjustment of a "new" fresh out of the box governor is set a little too high and requires adjustment. Seems the atmospheric pressure is different down in Mexico.

TomC · May 11, 2018, 08:39:35 AM

If you do buy a new governor, make sure it is adjustable. There are some cheaper ones that are sealed-no adjustment.
If you're having trouble with your AD-9, might be easier to buy a new one-not terribly expensive. I had to since mine was old enough where the correct rebuild parts were not made anymore. Good Luck, TomC

buswarrior · May 12, 2018, 04:22:23 AM

I don't know about other regions, but "trading-in" the entire air drier unit for a fresh reman is wildly popular around here.

You'll see lighter blue painted AD-9 hanging off trucks, that's a reman around here.

Someone to blame when it doesn't work, and not much different price from buying all the stuff and doing it yourself. You may have to order and wait for a 24 volt, but then busnuts areusedto that...

Happy coaching!
Buswarrior