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Old 01-22-2008, 04:32 PM   #1
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two air brake tanks?

was wondering why my bus has two airbrake tanks and can i replace both with one big one from a bigrig?
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Old 01-22-2008, 06:56 PM   #2
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Re: two air brake tanks?

You have two air tanks because one is a wet tank and one is a dry tank. The first tank is the one that will collect a lot of condensation and dirt. The second tank is what will actually supply the brake chambers and will generally be dry. I would actually be surprised if you didn't have a third tank somewhere like maybe along the rear framerails. One will be the primary tank while the other will be secondary. That is similar to the split hydraulic system you might have in your truck. If you only have one tank I bet it's actually a split tank.

The long and the short of it is that no, you can't just replace the tanks with one big one.
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Old 01-22-2008, 10:33 PM   #3
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Re: two air brake tanks?

just want to agree with the above post that you probably have either a split tank or two separate tanks.

most likely on your air guage, assuming you have a pretty modern bus, that there are two needles that usually move in unison, the needles are commonly orange and green i'm pretty sure. One needle is for the primary and the other is for the secondary system. if you loose air in one, you can use the second one as a backup to help get the bus stopped. if both run out of air, then the springs in the rear brakes should lock up the rear tires.
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Old 01-23-2008, 08:38 PM   #4
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Re: two air brake tanks?

so could i switch to a big single with a small backup? small wet big dry. why would there be a third. and refering to a split system, one for front one for back??
thanks
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Old 01-23-2008, 09:03 PM   #5
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Re: two air brake tanks?

Yes, there would be three because there would be a wet tank and then two individual dry tanks because of the duality of the system. It is also possible that your dry tank has a divider in it making for the two tanks within one.

Personally I wouldn't mess around with the tanks other than replacing them with something equivalent. You have to remember that all the components of an air brake system are matched to each other in terms of size and a capacity. Going to a larger tank might allow you more reserve capacity for the brakes, but a serious possibility exists that your compressor will not be able to build pressure back up within acceptable (legal) recovery times.

Why are you wanting to change them around? Are you just wanting to get some more room underneath? If that's the case I would just move the tanks somewhere else. I don't see any huge concerns with doing that.
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Old 01-24-2008, 04:33 PM   #6
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Re: two air brake tanks?

yes trying to make more room and also to replace old and rotten with new and modern. what do you mean duality, one for front one for rear? does one need more pressure? and do they really need to be seperated? i wnat to move them either all front or all back. would one way be better than other, asin if tanks in rear, more pressure from pump, if in rear slow response b/c of volume to brake. thanks
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Old 01-24-2008, 05:31 PM   #7
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Re: two air brake tanks?

Here is a site that gives a pretty good explanation of the topic:

http://www.saferoads.com/vehicles/sbcv_airbrakes.html

The short of it:

Quote:
In two axle units "primary air" is used for the rear axle brakes and "secondary" for the front.
Another more thorough explanation can be found at this site:

http://www.newbiedriver.com/ABCsUpda...rBrakes101.htm

The dual system is very important for safety. If one part fails, you still have the other. As for location, both of mine are in the same area (just ahead of rear axle). I don't think it matters where they are located.
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Old 01-24-2008, 05:50 PM   #8
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Re: two air brake tanks?

I suppose technically they don't need to be split, but you're taking a BIG risk there if they aren't. Remember really old cars with just single chamber master cylinders? Yeah, you lose one line and everything is dead. With a redundant system like the split tanks you're going to retain about 50% of your braking power should one side of the system fail. Personally, I'm all about piece of mind when it comes to stopping a 10 ton death machine on a 7% grade.
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Old 02-03-2008, 10:32 PM   #9
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Re: two air brake tanks?


I'll happily modify most things to suit me, but I would not fool with the air brake system -- other than relocating tanks of equal specifications, using new and correct hoses. Air brake systems are more complex that they appear at first glance, and the risk is too great.

Incidentally, Millicent has four tanks. It looks like just two tanks, but both are divided into two effective tanks.

I've been driving air brakes for a living for a quarter of a century, and I still don't know all about them. But I know to leave a good thing alone when I see one. (Sometimes. )
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Old 02-04-2008, 12:06 AM   #10
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Re: two air brake tanks?

Most heavy-duty vehicles use dual air brake systems for safety, and it is a federal requirement on school buses. A dual air brake system has two separate air brake systems, which use a single set of brake controls. Each system has its own air tanks, hoses, lines, etc. One system typically operates the regular brakes on the rear axle or axles. The other system operates the regular brakes on the front axle (and possibly one rear axle). Both systems supply air to the trailer (if there is one). The first system is called the "primary" system. The other is called the "secondary" system.
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