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Old 12-11-2006, 11:02 AM   #1
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Questions on air-operated doors

Hi All,

Ok, my new-to-me Thomas has a set of split air-operated entry doors. To the left of the driver's seat is a toggle switch with which to open and close the doors.

On my bus the doors appear to operate as they should but they will not stayed closed at speed; they pull open about 6" or so varying with wind conditions but anything over about 35 mph usually has them opening a bit.

I took the panel above the door apart and found a large air cylinder attached to the doors with various bits of linkage. All the air lines seem to be in good shape and when the toggle switch is repositioned the air cylinder appears to operate correctly. But...when the doors are closed I can push them open albeit against some amount of pressure but it doesn't take a huge effort. I also can't hear any air leaks above the door, in the cap compartment above the driver where the air line runs across, or near the toggle switch (which I suspect is electric and not air just due to "feel").

I don't understand what is really supposed to happen never having been around air-operated doors before. Once the doors are closed should there be enough air pressure in the cylinder to make it all but impossible to push the doors open? Is it air pressure alone that keeps the doors closed? I don't see any "latching" arrangement for a mechanical system.

I'm a little familar with air cylinders that receive air pressure to activate something then the air is released to return to a rest state. It appears the air actuator above the door in my bus may act like a hydraulic actuator and get "pushed" from each direction as necessary. Anybody familiar with the mechanism that does the switching for that? Or if it even happens with air actuators?

I plan to replace the split doors with a 1-piece swinging entry door but since that may not happen really soon I'd like to get the current door system working well enough that I can drive the bus without the doors opening on their own. It's a little disconcerting but it's also COLD!

Thanks!
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Old 12-11-2006, 10:54 PM   #2
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Your Thomas has air doors? Mine had mechanical doors. That was the first real thing I changed, put in a nice Larsen Security storm type door, has glass like in a windshield and triple locking mechanism....plus glass from top to bottom!!
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Old 12-11-2006, 11:44 PM   #3
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That's a tough one, Les. It doesn't help that I've never seen air doors (or the workings anyway). It sounds to me like you aren't getting enough pressure. Is there a regulator in there somewhere? Can you tap in and see? I have no clue what the correct pressure would be, but it seems like you'd be able to tell if the pressure is way too low.
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Old 12-12-2006, 08:40 AM   #4
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Quote:
Originally Posted by GoneCamping
Your Thomas has air doors? Mine had mechanical doors. That was the first real thing I changed, put in a nice Larsen Security storm type door, has glass like in a windshield and triple locking mechanism....plus glass from top to bottom!!
Hi Cliff,

I like your door; I saw it when I went back to the beginning on your site and read every post! I'd like to do that or something like it; I just wasn't planning on doing it quite this soon. Maybe I'll have to move that job higher on the priority list!
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Old 12-12-2006, 08:44 AM   #5
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Quote:
Originally Posted by the_experience03
That's a tough one, Les. It doesn't help that I've never seen air doors (or the workings anyway). It sounds to me like you aren't getting enough pressure. Is there a regulator in there somewhere? Can you tap in and see? I have no clue what the correct pressure would be, but it seems like you'd be able to tell if the pressure is way too low.
Yeah, my guesses are along the lines of yours; I know this shouldn't be too difficult (unless I have a bad cylinder) but I was hoping someone on the forums might already be familiar with the system. I'm not going to spend to much time or money on the situation because I am going to put in a regular swing door; I just wanted to wait a bit longer.

Thanks for the ideas.
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Old 12-12-2006, 11:34 AM   #6
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It could also be a small metal part above the front most door of the two that could be worn out enough to cause this or it may have broke.

This part on a bluebird is called a lever assy. in a bluebird parts manual.
http://www.skoolie.net/gallery2/d/13847-1/DSCN0384.JPG

I'm pretty sure a thomas will have the same set up on the door.
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Old 12-12-2006, 10:01 PM   #7
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If it's just temporary, just put one of those "outhouse door" ;atches on it and call 'er bad enough.
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Old 12-12-2006, 11:07 PM   #8
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Quote:
Originally Posted by the_experience03
If it's just temporary, just put one of those "outhouse door" ;atches on it and call 'er bad enough.
Same thought I had!
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Old 12-12-2006, 11:10 PM   #9
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Quote:
Originally Posted by wmah
It could also be a small metal part above the front most door of the two that could be worn out enough to cause this or it may have broke.

This part on a bluebird is called a lever assy. in a bluebird parts manual.
http://www.skoolie.net/gallery2/d/13847-1/DSCN0384.JPG

I'm pretty sure a thomas will have the same set up on the door.
I got into the compartment above the door a couple of weeks ago and checked out all the linkage. It actually all works pretty well; the thing that doesn't seem right is that I can push the doors open (with the switch in the closed postition) and watch the linkage push the actuator rod back into the air cylinder housing. I keep thinking that with air pressure in the right place I shouldn't be able to do that but that is still just a guess on my part. Still confused!
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Old 12-13-2006, 06:34 PM   #10
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Quote:
Originally Posted by jsham
On my 94 Thomas, I have a valve on the front bulkhead to the left of the door as you're facing outside that relieves the pressure on the "closed" side of the cylinder. Like you said, this is a double-acting cylinder, so it takes two different loops to open and close the door. This valve is labeled "emergency door release" or something of the sorts. Its a simple 3-way ball valve that either lets air flow straight through or exhausts the cylinder contents to atmosphere.

You might see if you have this valve and make sure its functioning properly. Its only connected to the "closed" side of the cylinder, so if you have the "open" side of the cylinder activated, this valve does nothing.

I've overhauled most of my air door hardware and pneumatics since I intend to leave it in place, so I'm pretty familiar with this system at this point. Feel free to ask if you have any other issues arise.
I do have that valve. When I first picked up the bus I finally found out it's why the doors wouldn't close even with the switch in the "closed" position. With the release vavle in the operating position the doors do indeed open and close when the driver's switch is operated. It's just when you then walk over to the doors you can push them open; albeit with some pressure. With the valve in the released position the doors are very easy to open.

When your doors are closed (and the valve in the operating position) can you physically open your doors with a push?

Also, out of curiosity, do you have an on/off air switch (mine has a yellow knob that snaps inward and outward with what looks like plastic fingers around the sides) off to the right of the driver's seat (as you're sitting in it) and just below knee level (on my bus it's under the radio)? For the life of me I can't figure out what it does...it doesn't affect the doors or so far anything else that operates on air (wipers, air horn, throttle).
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Old 12-13-2006, 08:08 PM   #11
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Les: I don't understand the "plastic fingers", but... Have you driven this thing yet? That yellow button sounds an awful lot like the parking brake to me. Pull to set brakes, push to release. If you are new to air brakes, it can indeed seem like a mystery.
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Old 12-14-2006, 11:33 PM   #12
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Hey guys,

Thanks for the good thoughts! In this case I do know it's not the parking brake; I've driven the bus quite a few times, my Blue Bird has air brakes and I'm an ex over-the-road Owner-Operator. The parking brake air valve is up on the dash to the left of the steeing wheel; what can I say...it's a left-handed bus...even the shifter for the Allison is on the left! The gizmo I'm talking about is to the right of the driver on a vertical panel that goes to the floor under the dash level (just below knee level). It's yellow (and much smaller than the brake air valve) and says "push-on, pull-off". It has air lines connected to the back of it. As for the "fingers"...around the valve, like surrounding the yellow knob part, is a plastic "cage" so to speak made up of these fingerlike pieces. I'll see if I can't get a photo of it and post it here. It is an on-off air valve; I just can't figure out what it controls as all the lines for it run inside the front dash area but regardless of whether it's on or off the air wipers work, the air horn works, the doors work the same, the air throttle (seemingly) does the same thing...just has me curious is all.
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Old 12-14-2006, 11:48 PM   #13
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Quote:
Originally Posted by jsham
Like the last poster said, that on-off switch sure does sound like a park brake switch.

When my air system is pressurized, it is nearly impossible to open the door by pushing on it.

I think the next thing I'd try is to test the pressure going to the cylinder. First, before you do any work on your air system make sure the tanks are depressurized! A 1/4" hose with 120 psi will leave quite a mark if it comes loose and gets you! Next, I'd buy a pressure gauge with a 1/8" NPT fitting. Unscrew the hose where it connects to the cylinder, connect it to the pressure gage, repressurize the system and run your open & close switch while noting the pressures. Also watch the gage for a little while and see if the needle moves, showing a pressure loss somewhere.

You may not want to do all that mess, but after doing that, you may be able to diagnose the system a little better. Or maybe you have messed around with things enough already to know that this would be a waste of time.

-Jeff
Hi Jeff,

Thanks for all the good info...much appreciated.

The pressure gauge test would be worthwhile. If I am getting full pressure at the acutator then perhaps the seal (or whatever it is inside) that separates the close side from the open side is letting air past. If I'm not getting full pressure then I can start chasing down the air line to see why not.

I'd rather use the doors as they are for a while before I tackle putting in a regular swing door. If I can get them to close tightly and seal I may just keep them as is...the air doors are pretty cool!
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Old 12-15-2006, 12:01 AM   #14
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Oh no, another old trucker! I still drive part time -- for Hendrickson out of Sacramento.

Boy, that little yellow button has me stumped also. Perhaps it was for some kind of school pupil transporting equipment, like a stop sign. My "Millicent" had a fold-out stop sign on the left, and a crossing bar (I don't know what they actually call it) on the front bumper, both operated by air. The school district probably disabled that equipment before they sold the bus.
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Old 12-15-2006, 12:10 AM   #15
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Quote:
Originally Posted by Elliot Naess
Oh no, another old trucker! I still drive part time -- for Hendrickson out of Sacramento.

Boy, that little yellow button has me stumped also. Perhaps it was for some kind of school pupil transporting equipment, like a stop sign. My "Millicent" had a fold-out stop sign on the left, and a crossing bar (I don't know what they actually call it) on the front bumper, both operated by air. The school district probably disabled that equipment before they sold the bus.
Ya know...that's a darn good idea. When I picked up my bus the stop sign arm was already removed. There's a good chance that valve might have been a way to keep it from swinging out when it wasn't appropriate. Now I'll have to trace that doggone air line to see where it goes!

Old trucker indeed...I'm not a day over *&! You know they say old truckers never die, they just get a new (ummm...truck!).
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Old 12-15-2006, 12:49 AM   #16
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Like this?



(Warning. Thread drift in progress. Warning. Thread drift in progress. Warni...)
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Old 12-15-2006, 01:19 AM   #17
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Did the bus used to have automatic tire chains? I can't think of anything else.
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Old 12-18-2006, 07:18 PM   #18
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Quote:
Originally Posted by Elliot Naess
Like this?



(Warning. Thread drift in progress. Warning. Thread drift in progress. Warni...)
Holy Mackeral! Now that's a beautiful rig! (I'm drooling on my keyboard!) Looks like a Prevost bus body mounted behind the cab...someone did one heck of a job.

[And yup...it's a Peterbilt! ]
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Old 12-18-2006, 07:23 PM   #19
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Originally Posted by the_experience03
Did the bus used to have automatic tire chains? I can't think of anything else.
No chains but it does have wheel sanders. There's a vertical on/on switch for them and I assumed that they're electric but I haven't chased that down yet...another good thought. At the very top of the photo below just left of center you can see the bottom of the sander switch.

The yellow gizmo in the ceter is the thing I've been asking about; you can see the "fingers" around the center of the switch. The outer ring is the one that pulls up and pushes down; the center is fixed.

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Old 12-18-2006, 09:03 PM   #20
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it sure looks like the adjustment knob on an air pressure regulator the lower ring pulls up to lock it in place. what on the buss uses adjustable air pressure? doors, sanders, ?
Look in the graingers or mcmaster carr catalog at their air regulators and it will become clear as mud.
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