I have a Bendix Tu-Flo 750 compressor on a Series 60 with a D2 governor (pretty standard stuff). It will not compress air when it is below freezing. It has never compressed air properly at below 32 degrees, but has worked fine at higher temps. There is what sounds like air loudly purging about every five seconds from the compressor.
The air dryer dessicant and purge valve were replaced 15,000 miles ago, rear tanks have auto drains, and the front tanks have been drained regularly. None of this should matter as this stuff is all after the compressor.
I was told by someone to replace the D2 governor to fix this issue. I did so and I am getting the same exact issue as before. I do hear an air leak from the compressor after the engine is off, but not sure if that was an problem before.
Where do I go from here? Still a governor issue or something else like a bad compressor or bad unloader valves?
I talked to someone about my issue and he said it is not the governor and is almost certainly a moisture/ice issue. It was explained that the unloader valves are purging air because the air being compressed has nowhere to go and the unloader valves will expel the air at 200 PSI for safety reasons.
Should I be unhooking the line from the compressor to the air dryer at the dryer to see if air is moving there? I would think the blockage has to be pretty close to the compressor to not let any air into the system at all.
as suggested air line heat will remove moisture from lines:sometimes referred to as air line antifreeze/ air compressor head bolts should be torqued to 440 to 500 inch lbs. to get ft lbs divide by 12 . take discharge line off air compressor and dump in then reattach.Is your dryer working?
Make sure the intake is clean if yours has a separate air cleaner for compressor change it and be sure the auto drains are working properly they give problems in cold weather
good luck
Isn't any sort of chemical to remove moisture/ice from air lines a no-no when the purge valve on the air dryer has a heater?
I'll have to check if the heater on the purge valve seems to be working.
This topic reappears every year and I don't recall any warnings - possibly because heaters in the dryer are pretty standard. Some buses have special antifreeze delivery systems permanently installed.
Quote from: Tony LEE on December 03, 2010, 01:30:02 AM
This topic reappears every year and I don't recall any warnings - possibly because heaters in the dryer are pretty standard. Some buses have special antifreeze delivery systems permanently installed.
Aren't the buses that had airline antifreeze delivery systems generally older models without air dryers?
All sorts of vehicles have air line antifreeze systems including modern ones, the point is that the air line antifreeze is introduced into the wet tank or some other location which is after the air dryer. The air line antifreeze is harmful to the desiccant in the air dryer, so it should not be introduced before the air dryer.
There are probably older installs before air dryers were common where the antifreeze was introduced right after the compressor, in which case they should probably be disabled or moved if an air dryer is retrofitted.
This sounds to me like the intake, discharge or unloader valves sticking. The air compressor continually compresses air, the unloader valve diverts it to atmosphere when told to by the governor. My manual says the unloader needs to be lubricated with a special lube, dimethyl polysiloxane, http://en.wikipedia.org/wiki/Polydimethylsiloxane (http://en.wikipedia.org/wiki/Polydimethylsiloxane)
It will apparently lube your unloader, keep your hair shiny, and make your Chicken McNuggets tasty and crispy. I kid you not, the things you learn on a Friday morning on the Bus Forum...
Anyway, I think you need to service your compressor.
Brian
Do you have power to the heater on the air drier?
It matters a whole lot in the cold.
happy coaching!
buswarrior
just thought of easy ck to see if it is compressor or air system blockage. Make you a adapter and either put shop air to the air system Thur air compressor discharge/delivery hose or discharge( from air compressor) into a separate portable tank with a gauge on it if you don't have shop air. would let you know where problem is for sure
Quote from: buswarrior on December 04, 2010, 07:00:19 AM
Do you have power to the heater on the air drier?
That is one of the first things I plan to check today when I go out to look at things again a little later. We got 6 inches of snow overnight which will slow things down a bit. If I have power how do I know if the heater element is really working? Will it be warm to the touch?
Heater has a certain resistance. Check the Bendix manual for the number and use your ohm meter settings on the mulit-meter to confirm continuity and the proper resistance.
happy coaching!
buswarrior
I found part of the problem. I assumed the air dryer is 24 volt so I installed a reman 24 volt purge valve. Well, when I tested the voltage today it only showed 12 volts. I double checked the wiring diagram and sure enough, the air dryer is 12 volt.
I found a place still open today where I can get a replacement purge valve. I'm not convinced this is my only problem yet.
Brian good catch! it's the simple ones that seem to get buy us. fingers crossed that's it Bob
A 24 volt purge valve is $90 at one place and $105 at C&J Bus Repair. A 12 volt version is only $50 on sale! I suppose they make a lot more of the 12 volt version. I hope they will take the 24 volt as a core.
A fair bit of moisture came out of the air dryer when I pulled the purge valve. I had tried to heat the purge valve, but maybe not long enough. I think I'm going to spend the $21 and replace the dessicant cartridge even though Dina made taking out the air dryer a 2 hour project. The space they choose isn't wide enough to get the wrench in easily to disconnect the lines.
You must have a cold weather leak some place cold air compresses faster than hot air so I was taught in school
good luck
Quote from: luvrbus on December 04, 2010, 11:59:31 AM
You must have a cold weather leak some place cold air compresses faster than hot air so I was taught in school
The safety valve on the compressor is releasing air constantly so I suspect a blockage more than a leak. I do have some cold weather leak somewhere as the air will drain out in a few days in cold weather, but air will stay up almost forever in warm weather.
I'm going to try a few more things before I give up and call in a mobile mechanic. I will take the bus in for a checkup on the air system once I get the air system flowing again.
you sure it's not the safety valve itself?
So what you are saying is your system has a discharge line safety valve if so those are designed to work when the line is frozen so like Pat said it maybe bad they cost around 20 bucks new change it.
good luck
I've talked to several mechanics about this. I'm not certain I have a safety discharge valve, but I probably do. The interesting thing is that everything works fine above freezing. I had this same problem the last time I tried to run the bus during freezing weather. That time I was able to run the bus at high idle until the engine warmed up enough to warm up the compressor and it started working.
I have more investigation to do tomorrow to see if I have a safety discharge valve. I will also be removing the air dryer to replace the cartridge and the purge valve. I will check to see if the line going into the dryer is froze up or not.
Brian,
If you have much moisture in the system you've already found the problem!
Moisture freezes in cold weather! Frozen moisture gets stuck in valves and holds them open where they leak. When they are leaking air won't build!
When you told us earlier that you were pretty sure that it wasn't a moisture issue as you had serviced the air dryer & had automatic drains I skipped this train of thought! ( by the way I hate automatic drains because when they get a little age on them they are more trouble that they are worth! ;))
FWIW
;D BK ;D
I wish I could be paid for this....and all the unnecessary maintenance you are about to pay for.
It works warm, it doesn't work frozen?
Settle down, get the PROPER parts installed and connected, system fired up...
And then the problem will be gone.
Read up on exactly what the innards of an air drier does. The purge valve, while FROZEN in the purge position, plugs the compressor output.
That is why the grizzled veterans of the coach and truck industry who went before, and I have repeated on these boards, that when parking the coach in the cooler months, lower the air pressure down to where the compressor is pumping before you shut down, so the purge valve can freeze in a good position, not a failure position.
In summary, returning to the issue at hand, a frozen purge valve prevents air going beyond the drier, the air pressure keeps building until the compressor can't squeeze it any higher, or something lets some air out.
I will collect in Arcadia.
happy coaching!
buswarrior
The interesting thing is I pulled the purge valve and started the engine after that. I thought air would free flow out of the air dryer, but still the same problem as before.
The main issue with the purge valve is that I bought the wrong voltage unit the last time I replaced the purge valve. My coach is primarily 24 volt so I just assumed the air dryer is 24 volt. It turns out to be 12 volt and the 24 volt element was probably generating little or no heat. I have a replacement 12 volt valve I will install this afternoon. I'm also going to replace the dessicant while I am at it.
I had replaced the purge valve and dessicant last about 15,000 miles ago, but it was three or four years ago.
So, the coach has been through a number of winters before this failure occurred?
Kinda important info for accurate troubleshooting...
Let the enlightenment continue!
happy coaching!
buswarrior
The coach has never compressed air properly below 32 degrees in the winter since I've owned it. The one other time I ran the coach in the winter I let the engine run on high idle for 30 minutes and it started working once the engine warmed up.
I got the air compressor issue fixed, mostly! I pulled the intake line off the air dryer and it was plugged with ice. I heated it for a bit with my heat gun and then started the engine. A 2" long plug of ice blew out of the line and air came rushing out like it should. I removed the air dryer and brought it in the house to that out before I replace the dessicant and the purge valve.
It seems all my problems started because I put in the wrong voltage purge valve. I'm going to hopefully get the air dryer put back in today. The governor was never the problem like someone told me.
Brian moisture in the airlines become "A 2" long plug of ice" and cause the ill effects you are experiencing.
As long as Ice is plugging the line it will never work properly!
What happened before it not so much that you ran the engine @ high idle for 30 mins. But rather the heater worked for 30 mins supply warm air until the ice melted! (no heater = no melt!)
;D BK ;D
The next frontier, you've got wet inside the system, and your next post will be lost functionality due to frozen valving. On your way to Arcadia
You need some brake alcohol pumped into the tanks.
Also, the automatic drain valves on those other tanks...
They don't work as advertised, and you want to see what is, or isn't, accumulating in your tanks.
Dump them for cable pulls and one knee on the ground, peer underneath when you pull to see what doesn't come out.
I posted extensively on recovering a polluted air system a couple winters ago for a busnut that the previous owner messed everything up. Ignore the out of context bits:
An outboard motor fuel line with the primer bulb, a female airline connector substituted in the outlet end, open pipe on the inlet end goes into the gallon of brake alcohol. Hold on to the fittings you cut off, someone will want them for the boat. And a couple gallons of brake alcohol.
The drains on every tank get replaced with a male airline fitting and a quarter turn valve. (This also makes taking pressure readings with a tire gauge and filling with the shop air an easy routine.)
Drain the tanks of air and whatever else will come out, and then pump a quarter to a half gallon of brake alcohol into each of the air tanks. You have 4 stock, one ahead of the rear axle, two behind the front axle and one up under the driver. If you find other places to store air.... well, I wouldn't be surprised, someone has been playing with it already.
Start bus, go for a drive, operate all air system components repeatedly, seats fill and empty, wipers, washer, brakes, service and parking on and off a dozen times or better, front door air lock. still have the radiator shutters? Go and use the bypass valves to run the air through and through out the system. Air horn? The air suspension is the devil, hard to get flow though that without having access to the height valving. Hope for the best on this one.
Leave the alcohol in the other tanks until spring, now, drain the wet tank, if you don't like the colour of what comes out, get your trusty primer bulb rig and pump in some more alcohol to help rinse it out some more.
Here endeth the quote from ancient history.
happy coaching!
buswarrior
BW, Is alcohol really the right substance to use for this? I thought someone said it is hard on seals and valves? Won't I reduce my air capacity by filling the tanks with fluid?
I've been thinking about it and I'm wondering how the air dryer could have had so much moisture in it? I know during normal operations I hear the purge valve let out a puff of air on a routine basis. The bus was last driven on the road about 4 or 5 weeks ago when it was above freezing. The previous owner was a charter operator that appears to be out of business. (Bus may be a repo.) They seem to have neglected the air system. The bus was 11 years old when I got it and it appears I was the first person to ever have serviced the air dryer when I did that 3 or 4 years ago.
I didn't finish getting the air dryer serviced today as I can't get the dessicant cartridge loose with my strap wrench. I have to take the old cartridge back as a core so I'll see if the parts place can get it off for me.
Yes, avoiding the use of alcohol in the air system is the preferred route, according to Bendix.
However, once the air system has been moistened, what choice do you have if you want it to work in the cold?
Never mind the loss of capacity for air due to some alcohol. Not significant versus the trade off of being functional. How do you know you aren't full of water behind those auto drains in the back?
The time for keeping the air system dry is 365 days a year, not after freeze up.
Too late for polite religious observances now... an exorcism is in your future...
If you are really pained by violating the coach with alcohol, in the summer, when this is all over, you may crack open the supply side of various valves (brake treadle, relay valves for rear axles) and give them a spray of your favorite good quality spray lube, one without a solvent in it, re-assemble and put it through its paces.
Get the air drier sorted out, dose the system with alcohol, get down to Arcadia, enjoy the coach during the cold weather, drain the rest of the tanks in the spring, keep the air drier and system in tip top operating condition from now on, never have a problem with freezing again.
happy coaching!
buswarrior
Brian - how is your compressor discharge line routed? From the Bendix compressor book:
The discharge line must maintain a constant slope down
from the compressor to the air dryer inlet fitting or reservoir
to avoid low points where ice may form and block the flow. If,
instead, ice blockages occur at the air dryer or reservoir
inlet, insulation may be added here, or if the inlet fitting is a
typical 90 degree fitting, it may be changed to a straight or
45 degree fitting. Shorter discharge line lengths or insulation
may be required in cold climates.
While not all compressors and charging systems are
equipped with a discharge line safety valve this component
is recommended. The discharge line safety valve is installed
in the cylinder head (Tu-Flo® 550/750) or close to the
compressor discharge port and protects against over
pressurizing the compressor in the event of a discharge line
freezeup.
Brian, if the ice had a antifreeze color or smell you have a blown gasket or cracked head on your compressor it will be ok if it was clear ice
good luck
Just as a reminder and not related to the air problem but are your batteries fully charged or at least on a charger? My guess would be that will be the next problem once you you your air problem sorted out! ;D
Quote from: buswarrior on December 05, 2010, 06:00:49 PM
However, once the air system has been moistened, what choice do you have if you want it to work in the cold?
Never mind the loss of capacity for air due to some alcohol. Not significant versus the trade off of being functional. How do you know you aren't full of water behind those auto drains in the back?
The time for keeping the air system dry is 365 days a year, not after freeze up.
Here are the things I do to keep up my air system. What else should I be doing? Using a 24 volt purge valve when it should have 12 volt didn't help things.
1. Service the air dryer on a regular basis. Last done 15,00 miles ago with a new purge valve and a new dessicant cartridge. (Also being done right now.)
2. Drain the front air tanks daily while on the road. I replaced the old drain valves with cable pulls. Only a tiny amount of moisture comes out. Rear tanks have auto drains and I will need to change to manual with cable pulls.
3. Monitor operation of system to be sure compressor is bringing up air up fast enough. Test low air alarm on a regular basis.
Ace, yes I have been keeping my batteries on my three stage charger. I just installed new batteries and I'll be damned if I am going to hurt them.
Your air system maintenance list sounds good.
stevet903 has a really good point about the routing of your line between the compressor and the air drier.
There shouldn't be a place for water to pool in the line.
I wouldn't trust Dina in this regard, customers in the north were not their thing.
happy coaching!
buswarrior
The heater in the dryer make no difference where it is 24 volts or 12 volts is not going to stop the discharge line from the compressor to the dryer from freezing up fwiw
good luck
Quote from: luvrbus on December 05, 2010, 07:10:59 PM
The heater in the dryer make no difference where it is 24 volts or 12 volts is not going to stop the discharge line from the compressor to the dryer from freezing up fwiw
The line froze right at the dryer. A fair amount of water came out when I removed the purge valve. (I had been heating the purge valve.) I really don't know if the right voltage purge valve would have helped or not.
Dina uses a 90 into the dryer and one of the previous posts says that is not recommended.
There is nothing that says a 90 degree fitting is wrong.
If there is freezing, you may remedy this with insulation, or try changing to a less restrictive fitting, like straight-in or a 45.
But, first, we don't know if you have a line problem, until we know you don't have an air drier problem.
If you are worried, just add a couple of feet of plain foam insulation from the HomeLowesDespot to the line ahead of the drier for now. Wrap some good electric tape around it all and get on with Arcadia.
No more maintenance ideas, put away your tools, back slowly away from the coach...
happy coaching!
buswarrior
Quote from: luvrbus on December 05, 2010, 06:20:40 PM
Brian, if the ice had a antifreeze color or smell you have a blown gasket or cracked head on your compressor it will be ok if it was clear ice
The ice was pretty black and oily. I'm wondering if the air compressor is passing too much oil and needs some work.
probably just dark from accumulation.
Ewen, I wonder about your insulation approach. I was told that the connection between the compressor and the dryer had to be very heat resistant. Most that I have seen are braided SS aircraft type "hose". I wonder what the heat would do to the type of insulation you are suggesting. Doubt that I would be a fire hazard, but I suspect the flame point of that material is pretty low.
A better solution might be to take some of the old silicone heater or radiator hose and slit it so that it could be slipped around the line. Regular rubber hose would probably work for a while, and would have a pretty high combustion temperature.
Jim
Quote from: rv_safetyman on December 06, 2010, 08:21:21 AM
Ewen, I wonder about your insulation approach. I was told that the connection between the compressor and the dryer had to be very heat resistant. Most that I have seen are braided SS aircraft type "hose". I wonder what the heat would do to the type of insulation you are suggesting. Doubt that I would be a fire hazard, but I suspect the flame point of that material is pretty low.
A better solution might be to take some of the old silicone heater or radiator hose and slit it so that it could be slipped around the line. Regular rubber hose would probably work for a while, and would have a pretty high combustion temperature.
Jim
Jim the air dryers on most buses other than an Eagle are located far away from the compressor.
MCI = in front of the steer axle
Setra, VanHool, Prevost ( = I think Dina) = in front of drive axle.
So BW's advice seems quite safe to me!
I also remember (I think) Clifford telling someone once that Eagle never had a "standard" mounting position for an air dryer and actually placed them several different places depending on the model/options.
(I could be wrong as to who actually said it, by I really strongly feel it was the Eagle yoda himself! ;))
;D BK ;D
Many of the big trucks use the foam pipe insulation on the last so many feet of the run to the air drier.
Yes, as Jim has pointed out, there has to be more decision making than is found on an internet board.
Putting insulation in the first so many feet of the discharge line after the compressor would not be smart. Consult the Bendix materials for extensive instruction on air drier installation, line routing, troubleshooting and the implications of adding insulation.
There needs to be a certain length of pipe withstanding the heat of compression, which needs to be shed before the air drier, but then there is the problem in cold weather operations of losing too much heat and accumulating a build up of frozen moisture on the walls, until it plugs.
The compromise in some installs is some bare pipe, and some covered pipe.
On a Freightliner, circa 2001, that I am intimate with, the air drier is down low ahead of the steer tire, behind the bumper on the passenger side, with the compressor up high, over on the driver's side of the engine. The pipe wraps its way across the front of the chassis, loosely following the structure of the radiator support. There are quite a few feet of insulation covering the last of the run to the air drier.
This has worked to an indicated -44 degrees, so Freightliner seems to have got it right!
A motorcoach is much less likely to employ insulation on the discharge line, as most installs are quite sheltered compared to the openness found under trucks.
However, in this case, we are talking about a Dina, which I strongly suspect was not particularly engineered for winter conditions. Mix in the attempts by previous owners and hired hands to keep it functional... all bets are off.
As for the compressor needing work, call us back when the build-up time has deteriorated, and at that point you may find the air drier is spraying black oil out the purge valve.
happy coaching!
buswarrior
Dina coaches in the USA are well known for problems in cold weather climates. All of the Dina engineers were in Mexico and they had never built a coach for sale in the USA before. Most of the problems have to do with the passenger heating system and the defrost system. I have copies of several service bulletins regarding extensive changes required to the heating system. They also had to add insulation to the heater hoses running to the defroster cores and cover up the grill openings in the front.
I have no idea if there are known problems with the air systems and freezing weather. They put heaters on the auto drains on the rear tanks.
I think you are well experienced with Dina's cold weather air system dysfunction!
Dina cannot deny the immediate and obvious issue of cold passengers and drivers.
Dina can easily blame the fleet for bad maintenance if there is air system trouble.
Auto drains come with heaters from Bendix, that was easy for Dina to do.
happy coaching!
buswarrior
I finally got the air dryer reinstalled last night. I've been working long hours at work on a big project and Friday was an off day for the project so I got home at a decent hour. It was also pretty warm yesterday. (28 degrees)
I still have not done as Bus Warrior suggested and added alcohol to the air tanks. I have all the parts but I ran out of time last night.
tick tock - tick tock - tick tock
LOL