| Author | Message | ||
| Grant Thiessen (Busshawg)
Registered Member Username: Busshawg Post Number: 253 Registered: 10-2007 Posted From: 206.45.93.160  Rating: N/A |
I have a bad air leak coming from the valve on top of the drive axle that has all this air lines hooked up to. Think it dispurses the air to each brake chamber. The leak only occurs every so often when the brakes are applied. Sometimes dropping my pressure very quickly and sometimes just a small leak and other times not at all. To my surprise it is not coming from the exhaust valve on the bottom of the valve but rather from the top. Not sure where exactly, just that the pitch of the air leak changes when I place my hand on top of it. I need some opinions on this, could it be just some crap in teh valve or is teh vavle shot. It dd the same thng last spring and I contributed it to condesation and crap in the line so I installed a new air dryer. This worked for us all summer , approx 6000 miles. Now I'm thinking I should replace this valve. Grant | ||
| Grant Thiessen (Busshawg)
Registered Member Username: Busshawg Post Number: 254 Registered: 10-2007 Posted From: 206.45.93.160 Rating: N/A |
Oh one more question, is it possible for the air to be feeding back through the brake chamber. Hate to replace the valve and find out it was a brake chamber. Grant | ||
| FloridaCliff (Floridacracker)
Registered Member Username: Floridacracker Post Number: 429 Registered: 7-2004 Posted From: 97.101.146.143 Rating: N/A |
Grant, Very common to be back feed from a diaphram. You know the safety drill when under the bus. Clamp off one line at a time going to the brakes and you will be able to tell where its coming from. Cliff | ||
| Grant Thiessen (Busshawg)
Registered Member Username: Busshawg Post Number: 255 Registered: 10-2007 Posted From: 206.45.93.160 Rating: N/A |
Thanks Cliff, and I have it up on rail road ties. Thanks for the concern | ||
| Jack Conrad (Jackconrad)
Registered Member Username: Jackconrad Post Number: 1283 Registered: 12-2000 Posted From: 71.71.3.170  Rating: N/A |
Grant, If it leaks when the parking brake is applied, it is probaby a DD3 parking brake diaphram. If it leaks when the service brake is applied, it is probably a DD3 service diaphram. Cliff's method will determine which wheel. Jack | ||
| Tim Brandt (Timb)
Registered Member Username: Timb Post Number: 527 Registered: 10-2003 Posted From: 74.244.14.221  Rating: N/A |
Guys unless I'm missing something a diapham can't be intermitant it eaither blown or it's not. Am I wrong? (Message edited by timb on May 08, 2010) | ||
| George M. Todd (George_todd)
Registered Member Username: George_todd Post Number: 1010 Registered: 8-2006 Posted From: 99.29.76.171 Rating: N/A |
Grant, If the valve has two lines going to each drive axle brake can, and a line to a reservoir, and one going up front, it is the inversion valve which controls the parking and emergency brakes. If you have no idea how old it is, you should change it. The relay valve is back there too, but it only has one line to each brake can. Same thing applies to changing it out also. G | ||
| Buswarrior (Buswarrior)
Registered Member Username: Buswarrior Post Number: 1854 Registered: 12-2000 Posted From: 174.89.174.245  Rating: N/A |
Hello Grant. That is your inversion valve, with 6 airlines attached to it. It is a form of relay valve and is the heart of a DD3 parking system, and if its age is unknown to you, changing it, and the parking control push/pull valve beside the driver, is good preventive maintenance, especially when you have had trouble with it before. Its purpose is to direct air pressure to the parking portion of the DD3 chamber when parked, and when driving, release that air and to direct air pressure to the locking ports for their release. To further complicate matters, the service brake circuit is also plumbed to it via the parking control valve beside the driver, for anti-compounding, when it is in the parked position. That is why the parking control valve shouldn't be ignored in a DD3 system as it might be in a spring brake system. If the inversion valve, or it's control, the parking control valve beside the driver, is sticking in partial movement, seals are leaking or otherwise not moving smartly and airtight....you might have a show stopping event. It will leave you stuck, or unable to park, or with a potential to drag a brake. The only proper place for air to exit an inversion valve is through the exhaust, when it exhausts the air pressure in the parking portion of the chambers on a parking brake release. Otherwise, there should be no air leaving via the inversion valve. If air seeps out of it while parked, the inversion valve is bad. If air seeps out in driving configuration, the inversion valve is bad. If air seeps out in driving configuration with a service brake application, a parking diaphragm is leaking (there may be a little seep on application, as the park diaphragms are squeezed into the back of the chamber. I mean once it is holding and stabilized) Also, a leaking parking diaphragm will leak out via the service brake relay valve exhaust in a parked configuration, with no service application. A leaking lock port in a chamber will leak to atmosphere via the push rod outlet of the chamber when in driving configuration. However, before jumping to conclusions, confirm the service brake relay valve has not failed, that the leak goes away when in a driving configuration and no service application. And/or, drain the parking tank and confirm pressure available in the service tank only. The service relay valve can leak on its own by its own failure. Clear as mud? happy coaching! buswarrior (Message edited by buswarrior on May 08, 2010) | ||
| Buswarrior (Buswarrior)
Registered Member Username: Buswarrior Post Number: 1855 Registered: 12-2000 Posted From: 174.91.147.179 Rating: N/A |
ACK! I typed in error in the last paragraph. I originally typed: However, before jumping to conclusions, confirm the service brake relay valve has not failed, that the leak goes away when in a parked configuration and no service application. "PARKED" is wrong, I corrected the original post to read "DRIVING" My apologies to anyone who read or copied this before I corrected it. happy coaching! buswarrior | ||
| Grant Thiessen (Busshawg)
Registered Member Username: Busshawg Post Number: 256 Registered: 10-2007 Posted From: 206.45.93.160 Rating: N/A |
Thanks guys. As you must remenber BW I had some issues last spring with air laeking from the inversion valve. I ended up replacing the air dryer and parking brake valve. It all worked flawlessly all last summer. Now this past week-end the inversion valve was still leaking after I had drained the air tank a couple of times only when the brakes were applied. The puzzling thing was that it was leaking from the top where that little guard or whatever it is is located. It looks like it had been on the bus a lot longer than the brake cans, so I removed it last night and will order a replacement today. I think the problem is the inversion valve, however if not it has been replaced. Upon removing it I could tell it has been on there for a very long time as I had to use a hammer and chisel to seperate it from the cross memeber due to the corrosion from the aluminuim and steel. Is it a good idea to use some grease inbetween these components when I put the new one on? Thanks once again. | ||
| Buswarrior (Buswarrior)
Registered Member Username: Buswarrior Post Number: 1859 Registered: 12-2000 Posted From: 174.91.144.30 Rating: N/A |
Yes, put the anti-seize of your choice on the fasteners, and FWIW, I put a light coating on all the touching surfaces of the new airlines I installed on mine, under the bolts under the fitting, not on the sealing surface, if you know what I mean, so that I could have a shot at getting them apart properly and re-using them at some point in the nearer future. I have chamber maintenance to do, so I'll see how successful I have been with this process since I did it 4 years ago. The air fittings were rusted solid and had to be cut to get them off. I also just used the sawzall on the big nut on the inversion valve. Feel good about changing it! happy coaching! buswarrior |