Can't for the life of me find the air dryer line out of the governor

[RickB]

Switched out my engine from an 8v71 with an 8v92. I have two air fittings on the compressor governor. One goes to the reservoir air pressure signal which I'm assuming is the switch with electrical connections to it... The other is supposed to go to the air dryer purge line. The problem is I can't find any unused air lines anywhere in the air compartment. I ran air into the system last nite and capped the line to the governor (see photo) and the only leak I could find was in the bottom of the compressor governor.

I guessed the first time I hooked up the one air line I have attached to the governor and it pressurized my cooling system and I had coolant going into my air system.

I hate this... I can't find my manuals and I have no idea how to hook up my air system correctly.

The bus is currently in my warehouse and I need to get it out soon so any advice would be greatly appreciated

Rick

[buswarrior]

the line out to the air drier is for the purge valve signal. It is a dead end, so the only way to get it to expose itself is to blow air back from the purge valve fitting.

Always another punishment for a busnut?

happy coaching!
buswarrior

[luvrbus]

The purge valve line will be a 1/4 line from the governor to the dryer on about all buses,look at the old engine it may be in different ports on the governor vs the new engine,your dryer may be picking up the signal from the front air tank,you should have 1 line from the compressor to the pink tank from the compressor discharge and 1 water cooling line from the engine going to the compressor 

[GnarlyBus]

Here's a link to the manual for the MC-9: http://buses101.com/mc9_maint_manual.htm

[GnarlyBus]

Here's how it's setup on my 9:

1 is the air reservoir line which receives pressure from the supply tank and is hooked up to the Reservoir port on the governor. There's nothing electrical involved in this. It simply receives air from the reservoir and when the psi in the reservoir reaches about 120-130 (depending on adjustment), it pushes the piston inside the governor over and holds it there until the psi goes down. This allows air to open the unloader valves on the governor and cause it to make no air. Many great videos on YouTube about how the D2 governor works.

2 is the purge valve control line and is hooked up to the unloader port on the governor. I added a ball valve to my line to be able to shut this off if i ever had purge valve issues again.

These are the only 2 lines going to my governor. The unloader port on the compressor side opens the unloader valves and causes the compressor to not make air.

Line 1 goes up to the top of the engine compartment to the junction where the diesel fuel line is also.

Line 2 heads more towards the driver's side of the engine bay and is hard to see. I reached over and snapped a pic for you.

Let me know if you need any more pics or info.

[luvrbus]

Best to go by the book but there are a 100 of ways to make it work,any where the dryer or governor can pick up a pressure reading, you have the supply line going to the dryer and a outlet line to fill the tanks, if you get those 2 crossed the check valve will prevent the dryer from filling the tanks ,only ectric wire is for the heater.If you filled the cooling system with air you or water in the tanks  you have the air supply hooked to the water cooling for the compressor   

[bevans6]

The line to the air dryer purge valve is the fitting with the hose between the two bolts that fasten it to the compressor.  The other fitting close to the end of the governor is the air supply from the air system that tells it what the pressure is.

[RickB]

Thanks everyone for the advice...

Found the air dryer line, it had broken off when i removed my 8v71 so it's no wonder I couldn't remember taking it off.

So I have it hooked up correctly. One end to the air pressure signal generator and the other to the air dryer purge. However, it leaks air out of another fitting on the bottom. Running both my compressor and the bus engine I was unable to get above 65lbs so moving the bus out of our warehouse was not happening. I'm wondering if it still isn't hooked up right or if I broke something inside the governor when I hooked it up wrong. I tried capping the fitting on the bottom but then the air started coming out of the actual end of the governor. I didn't plan on taking up my warehouse bay this long and I'm gonna have to find a solution soon as we have a looming event that will require all my attention and the shop as well.

I wish I understood the philosophy behind the governor better. It's hard to fix something when you don't understand the idea behind the part.

Rick

[Bill Gerrie]

Video of D2 governor installation.

https://www.youtube.com/watch?v=FHGcXvDmZ5E

[bevans6]

An air governor is a cylinder with a supply port, a couple of delivery ports which go the the compressor unloader and the purge valve, and a spring loaded piston with O-rings inside the cylinder.  If pressure at the supply port is below 120 psi, the spring keeps the delivery port closed.  That means the compressor is loaded and working and the purge valve is closed.  As soon as air pressure gets to 120 psi, the spring pressure is over-come by the air pressure acting on the piston, it moves up and opens the delivery port so that air pressure is sent to the compressor unloaders, and the purge valve opens.  It sits like this - delivery port open - until air pressure falls to 95 psi.  At that point the spring pressure overcomes the air pressure and the plunger moves back and closes the delivery port, so the compressor compresses again and the purge valve closes again.  That is simplified, it's a tiny bit more complicated than that (there are actually two springs and some other gubbins) but not much.  Some are preset and not adjustable, some can be adjusted, most have a 25 psi delta between open and closed, and 95 psi - 120 psi is commonly what buses are designed around, some modern buses are higher than that.  The three holes at the base of the cylinder are the supply ports, you use one and plug the others normally, the three holes around the middle of the cylinder are the delivery ports, normally one is bolted to the compressor with a gasket and the others are plugged or go to the purge valve, and there is an exhaust port closest to the spring cap.

https://www.manualslib.com/manual/392610/Bendix-D-2-Governor.html

[bevans6]

"it leaks air out of a fitting on the bottom"   What is "it" that leaks air?

Brian

[bevans6]

The thing to remember about the purge valve and the air governor, and actually quite a lot of stuff, is that they don't work until they have air pressure.  The governor basically does absolutely nothing until it senses that it has 120 psi at the supply port, and only then does it unload the compressor and open the purge valve.  The purge valve does absolutely nothing until it gets sent 120 psi of air pressure from the governor - until then it does nothing but sit there.  If you have a massive leak below 65 psi and you have a MC-9, probably it's not the governor or the purge valve if they are hooked up correctly, and working properly.  If memory serves you have a 1982 MC-9 - it should feed the air governor from the accessory system, which is after the pressure protection valve, so it will not see air at all until the air system is up over around 65 psi.  At the same time, if you air up somewhat normally to 65 psi or so, and only then get a massive leak, it's after the PPV and could well be the plumbing to the governor.

Final thought - you kind of imply that you didn't disconnect the line from the governor to the purge valve when you pulled your engine out.  You might have also forgot to disconnect the supply line to the governor.  That line tee's off and feeds all of the air systems in the engine compartment, so you might have damaged that tee, or those lines, and they will certainly leak like a SOB once the pressure gets over 60 - 65 psi.

[RickB]

Bevans,

Thanks so much for your help. The 'it' that's leaking is the compressor governor out of a bottom fitting. I'm going to have to go look through all of this again tomorrow. Needed a day off. I'm so close but I just can't quite get it across the finish line. Tomorrow I'll get it figured out, I'm confident that there's only so many things I could have done wrong. Call it blind optimism... LOL

My guess is I don't have anything supplying the air to the governor after reading your overview.

Rick

[bevans6]

Rick, I just posted (cross-posted from Facebook actually) an MCI air brake 101 that I wrote the other day, when a guy there was having issues and it seemed like starting from the start might help.  It might also help you a bit.

The air governor is a universal fit deal and has several extra ports that need to be plugged.  There are three supply ports at the butt end of the cylinder, three delivery ports at the middle of the cylinder and one exhaust port near the spring cap end of the cylinder.  You need to have the unused supply and delivery ports plugged - usually two plugs in the supply and one plug in the delivery, since you are using two of the delivery ports for the compressor and the purge valve.  You MUST NOT plug the exhaust port, since it is was releases air and allows the governor to cycle.  If it is leaking air (one port, on the underside of the cylinder so it points down, nearest the spring cap) then there is indeed a problem with the governor and you could probably swap over the one from your old engine compressor.

Edit: in your first pictures, the bright shiny fitting is the supply fitting, and it doesn't look like it has a pipe in the compression fitting.  On my bus, the hard lines terminate under the floor, I access them through the hatch in the floor under the bed, and there are flex lines between the hard line termination and the governor.

Brian