| Author |
Message |
A.K.A. Captain Cry Baby (Captain_ron)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Friday, February 11, 2005 - 6:50 pm: | |
How long should the air pressure stay up in my 4905? I have a new compressor and it gets up to 120 + after I shut it off how quickly should it drop? |
jimmci9 #2
Rating: N/A
Votes: 0 (Vote!) | | Posted on Friday, February 11, 2005 - 7:02 pm: | |
depends on how many leaks you have.... i've seen vehicles sit for weeks and still have enough air to release brakes... while others start leaking down as soon an the engine is shut off.... |
Sojourner (Jjimage)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Friday, February 11, 2005 - 7:04 pm: | |
How long should the air pressure stay up?
If it air bag-equip, then whenever air-leveler’s lever move (wind rocking or walking inside or stepping in or out) will require air from supply tank to correct leveling.
Otherwise it should hold well + or – temperature change.
FWIW
Sojourn for Christ, Jerry |
Frank allen
Rating: N/A
Votes: 0 (Vote!) | | Posted on Friday, February 11, 2005 - 8:24 pm: | |
Air pressure on my 06 gauge drops over night but the suspension stays up for months, it has a small leak behind the gauge.
Frank allen
4106 |
Brian (Bigbusguy)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Friday, February 11, 2005 - 11:01 pm: | |
The main brake air tank on my 4905 will not lose any air for weeks . The other tank that is the tank next to the wet tank will hold air for about three days over night its still at 60 psi. The drain valve leaks a little.
The air bags hold for weeks.
The only way your going to fix air leak is with a shop compressor so you can hear them and some soapy water to find leaks you dont hear.
You will need to remove the covers in the bays there is fittings in there that could be leaking.
Under the driver area there is lots there that can leak . The foot valve can leak air out the exhust if it bad.
No bus should leak all the air out in a few hours.
Every leak can be found and fixed most only need a fitting tighted. The only things I had to replace was all of the low air switchs and I rebuilt the foot valve . And changed out my wiper controls so they shut off the air to the wipers when not in use.
Also lots of air leaks will cause lot of water and over work the compressor.
Pick up a truck and bus drivers hand book given out at most DMV office and it should tell you what will pass a DOT inspection with air leaks.
I would not pull into a road side truck check point with air leaks and ask them to give you a Inspection if you fail you will be stuck there until its fixed. Fix it first.
Brian 4905 Klamath Falls Oregon |
Johnny
Rating: N/A
Votes: 0 (Vote!) | | Posted on Saturday, February 12, 2005 - 12:06 am: | |
The GMC at work will hold ~95psi for a week or more.
The 1972 F-800 at my other job bleeds down to <40psi in about 4 hours, & to zero overnight.
Depends on how many tiny leaks you have. |
Chuck Newman (Chuck_newman)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Saturday, February 12, 2005 - 12:09 pm: | |
I have a 102A3 that air builds normally to 120 psi, then I hear a blow off in the front of the bus. This is followed by a gradual reduction in pressure to 90 psi, then the pressure starts to build again to 120 psi, then the cycle begins again. This appears to be a continual cycle whenever the engine is running.
Someone mentioned a bad unloader valve on the compressor. I haven't had a chance to dig into anything yet, but looking for pointers. Can this be related to the unloader valve? Or is the front area blow off possibly a high pressure protection valve that blows off at too low a pressure? Or something else?
Any ideas where to start looking would be appreciated.
Chuck Newman
Oroville, CA |
Jon W.
Rating: N/A
Votes: 0 (Vote!) | | Posted on Saturday, February 12, 2005 - 1:23 pm: | |
I think the potential for leaks is directly related to the complexity of the systems. To find a leak I know of two good ways. The first is to get the bus in a very quiet place and get under it and listen.
The second is to squirt soapy water at every possible site for leakage.
My older Prevost which has a complex leveling system took me a long time to identify every leak, and even longer to rebuild or replace the problem areas. That coach had about 15 Norgren spool valves just related to the leveling system so the goal of a leak free coach was a challenge.
I got it to hold pressure for a week and for the bus to sit on the airbags without leaking or leaning for almost two months.
The newer Prevost doesn't get the leans or lose air pressure on either of the primary systems for at least two months (the longest it has gone without being used by me), but the auxiliary air system which deals with everything from the sliding floor, door lock, belt tensioners, pocket doors, driver's seat, etc. goes to zero in about 12 hours. |
Buswarrior (Buswarrior)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Saturday, February 12, 2005 - 3:25 pm: | |
Hello Chuck.
First, the process you describe in the post above sounds normal. The purge you are hearing is your air dryer purging the accumulated moisture from that cycle of the compressor pumping up the air pressure.
Second, the needle is gradually dropping because you have air leaks somewhere.
In another post about air gauges, you also indicated you have a single needle air gauge in the instrument panel. MCI continued to plumb in a single needle air gauge for many years after the service braking system was split, by government regulation, in 1975. You'll have to check your air schmeatics to know where it is connected in yours. My MC8 has a single needle gauge plumbed into the "accessory", thereby showing the system pressure "ahead" of the check valve protected "brake tanks"
MCI didn't put dual needles, plumbed directly to the two service tanks (popularly called primary and secondary) in until fairly recently, in terms of the age of most of our equipment.
Because of this plumbing choice, you cannot troubleshoot what is leaking from the driver's seat. The accessory system is plumbed so that it backs up the rest of the system, much the same as the wet tank does, so it will show a drop in air pressure for any leak.
Before you go off worrying about complicated and expensive failures, air up your bus, shut it off and go outside and listen. And don't jump to conclusions just because you think you hear the air coming from "over near there". You don't know until you have sprayed soapy water and seen the bubbles, or put your hand and felt the wind. Leaking air sounds always seem to bounce off and come from the wrong direction, misleading those who haven't been caught yet!
A warning about us on here: We busnuts here are known at times to suggest the most obscure, expensive and complicated failure to something which might just need tightening with a regular screwdriver...
For example: You might just have a badly leaking radiator shutter piston, easily stopped temporarily by shutting the shutterstat air supply, and find the rest of your bus holds air for weeks.
Get your maintenance manuals, and seek out a course at your local college on air brakes. Even if you just buy the textbook, you'll be further ahead on being safe and knowledgeable.
happy coaching!
buswarrior |
TWODOGS (Twodogs)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Saturday, February 12, 2005 - 3:27 pm: | |
newman....not supposed to act like that...find where the leak is up front...maybe ,it's a burp valve...supposed to burp when it gets to 120 & stop imediatly....this constant cycleing will create loads of water and wear...my bus will leak down overnight...which I need to fix...can't hear good enough to find out where to fix...need to find some kid that hasn't been around incomeing... |
Leslie Robinson (Lesrmc9)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Sunday, February 13, 2005 - 1:11 am: | |
Hey guys if you have wire braded (black) air lines the oil that gets pumped by the compressor ( although very little) over time builds up and breaks down the "rubber" liner, so use soapy solution not only on the fittings but all along the braided hose, you will never hear this type of air leak but will have lots of suds |
Chuck Newman (Chuck_newman)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Sunday, February 13, 2005 - 1:32 am: | |
Great advice. Now I have a plan. Thank you to all for the input. And thanks Buswarrior for the info on the air system layout. I'll block it up with railroad ties, hook up the garage compressor, and get on my back. At least I have concrete to work on. Many thanks to all.
Bruceknee, thanks for the email. I don't know when I'll be able to get back to you. Can receive email but cannot send for past three days. SBC disconnected all DSL users that use third party internet service providers. Am working to get full email service back. May take a few days.
Thanks for the info.
Chuck Newman
Oroville, CA |