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filtering your brake/other compressed air

808pants

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Honolulu, HI
I've been pondering hardware options to filter my onboard compressed air, I think before it goes into the tanks, since chronic high humidity and oily crap are obviously doing a number on my air-packs. My first thought was to use something from the ground-based world of compressed air, like maybe a 'motorguard' toilet-paper style filter. A local vendor suggested I look into DOT-approved standard heavy-truck air-filters, but Google fails me on that score. Anyone have experience with particular filtration devices?

Also, does the low-air-pressure warning sense directly from the tanks, or is it out on a line somewhere? (I want to be sure that as my filter plugs, I know about it before I lose brakes...)

--Dave
 

Jimma

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Hartwell, GA
Interesting idea of adding a filter. The oily crap I dont think is that big of a deal because as it accumulates it drains out when you flush the air tanks. After draining them regularly mine does not seem to build up much gunk any more.
 

808pants

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Jimma - while searching for info on rebuilding my air-pack a few months ago, seemed like half the related posts included people with locked-up air-packs, and people suggesting they add oil to the little port behind the piston, etc. In my case, I'm probably much worse than the next guy in terms of remembering to drain my compressed-air tank, especially if there's a chance I am going to restart the engine soon - always hate listening to that ****ed warning buzzer while using hundreds of horsepower to run the tiny compressor - but when I do drain the tank, it's pretty heinous, even after a relatively short period of running. Some oil, LOTS of water. Imagining that stuff sloshing and scraping around the air-piston seal against my newly-rebuilt plain-steel air-cylinder bore makes me badly want to improve the setup. Also want to get an auto drain valve in place...
 

Jake0147

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782
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Location
Panton, VT
I've been pondering hardware options to filter my onboard compressed air, I think before it goes into the tanks, since chronic high humidity and oily crap are obviously doing a number on my air-packs. My first thought was to use something from the ground-based world of compressed air, like maybe a 'motorguard' toilet-paper style filter. A local vendor suggested I look into DOT-approved standard heavy-truck air-filters, but Google fails me on that score. Anyone have experience with particular filtration devices?
As to the need or validity, maybe... don't rule out mechanical conditions here either. You should get a little something daily, but it shouldn't be that much with no filter.
As for Google failing you, don't look for a filter. What's approved and accepted and semi-standard in the trucking industry does exactly that, but it's called a "dryer". Truck shops, parts stores that deal with truck parts, and even Google are far more familiar with that term. Since it's a retrofit, pretty much anything will fit, and the sky is the limit. Check the install instructions online first. (All the major manufacturers have that). Some have unique install requirements that may or may not meet your needs and/or desires.

This may help. Bendix is a recommendation, but I'm not knocking ANY brand that's out there, they're all good and Bendix is not always the least expensive. When it counts "axles", it's looking for air brakes. You do not have that. Your hydraulic brake booster (airpack) accounts for less than one axle. Use one axle and no lift axles. If you tow trailers, count each axle for full air brakes, or one axle total if it's air over. For the air wipers if you're not afraid of driving in the rain, add another axle. These are not high demand systems at all, if you come up with a 2 it does not mean you are shortchanging yourself, you just can't burn up as much air as a four axle tractor with a four axle trailer, eight axles worth of airbag suspension eighteen brake cans needing to be filled each time you tough the brake pedal, maybe an air ride cab... Air ride anything dumps all the time, they are PIGS and need very large system capacities.

http://www.bendix.com/media/documents/products_1/airtreatment_1/BW2600a.pdf

Also, does the low-air-pressure warning sense directly from the tanks, or is it out on a line somewhere? (I want to be sure that as my filter plugs, I know about it before I lose brakes...)

--Dave
Yes, as does everything else on the truck. It actually does come from "out on a line somewhere", but if you were to rectify that it would still come from "out on another line somewhere", even if it's a line you put in. The tank is in fact no more than a fat section of line. I see exactly where you're going with this, and it's kind of a valid concern, but misguided at the same time. You can not sense the pressure everywhere at once. even if you had a gauge directly screwed into the tank, you can't sense the pressure at the end of the lines that supply the actuators (including the airpack), any of which can "plug" just as easily as any other, including your cab supply.

Lines can be restricted. With the gauge being at the far end of one of the easiest to become restricted, it will be the first place to show problems, and will show problems long before the tank pressure drops. If the tank pressure should drop, the shmutz stuck in a necked down fitting will be stuck from the tank side, so the pressure in the line will be an effective back flush, being in the opposite direction. Even if you could find a permenant blockage that couldn't be backflushed, that cab supply has the highest concentration of "normal leaks" that you'll ever find, demanding constant charging from the tank. If the flow stops, the pressure drops QUICK in that line. I don't think you could do better.
 

808pants

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Location
Honolulu, HI
Jake,

Thanks, good stuff. I think you weren't following my concern WRT the low-pressure-alarm-switch (vs. gauge) location, though - my concern was that I not place my filter (dryer) such that if it blocks up, it won't leave the air tanks on the low-pressure side, thus not alerting me to a dangerous condition. This is seemingly quite possible, what with the forest of dark, hidden copper lines snaking through the insides of the frame. If I got that wrong, then when my filter blocks up, the tanks would go low on pressure, but the section of tubing between gauge and compressor (and maybe the switch, too) would stay right up where it might look like I'm safe, even though there might not really be enough pressure in the tanks for effective braking assist.

It occurs to me now that the frayed wires leading to a pressure-switch up and behind the air-pack (in that same mess of dark greasy tubing and wires within the hollow of the frame channel) might have been going to my low-air-pressure warning switch, and not to my brake-light switch, as I had assumed when I was fixing those insulation problems a while back. Essentially, I want to be sure the low-pressure warning switch - wherever it really is - isn't conceivably blocked from sensing tank pressure.

Going to Google now with "Bendix dryer" as keywords...though the more I think about it, the more I am convinced I'd be fine with a non-DOT-rated filter/dryer setup as long as I ensure that the low-pressure switch does indeed give me a dependable alert. That, along with changes in pedal feel, should get my eyes onto the pressure-gauge to spot a real problem if it's developing...right? Hmmm...wonder how quickly I could stop my loaded dump-truck without air assist...
 
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