on board air options

Post by **Steinberg** » Sun Jan 07, 2007 1:34 pm

so it turns out I'm too cheap for the powertank concept to work. my nitrogen tank lasted a while sure, but I'm also in need of a continuous source of air for my "shop", which is a parking lot, so I'm converting the AC compressor for true OBA. the N2 tank just doesn't cut it for running tools and such.

I'm weighing tank options now. I can fit a tank under the bed and out of the way, but I lose portability. OR I can get one of those porta-tanks and strap it in the bed and plumb it with quick disconnects so I can carry it down the trail or wherever else.

what I'm wondering at this point is if I don't have the tank in there, can the OBA still function properly with just the air lines? It will have an automatic pressure switch, so it seems to me like once you start inflating a tire, the pressure in the lines will drop almost instantly and the compressor will kick on. then when you pull the chuck off the tire, the pressure in the lines will very quickly go up and the compressor will kick off. I think this will work okay, but I'm a little concerned about whether the pressure switch will kick off quickly enough so that there isn't a pressure "spike".

I think I've got everything straight in my head, but if anybody has some input I'm listening.

Post by **Ctrow** » Sun Jan 07, 2007 7:00 pm

My step dads been runing his converted ac pump on his cj without a tank for years. Works just fine.

Post by **Steinberg** » Sun Jan 07, 2007 7:04 pm

okay, here's an actual question:

do I need an unloader for this setup, or can the AC compressor's clutch handle starting under load?

if I don't need the unloader, I can use an ARB pressure switch (110/150psi on/off) for about $20 and just a check valve. to have an unloader, it would take a ~$35 120V style switch and a check valve w/ unloader port.

I like the pressure range of that ARB switch and I doubt I'd find that in a cheap 120V style switch.

Post by **Ctrow** » Sun Jan 07, 2007 7:13 pm

i don't think you need an unloader, but i'm not positive. I know you don't need one if you're not running a tank.

Post by **yotacowboy** » Sun Jan 07, 2007 8:27 pm

what about running a small buffer tank under the hood (like an ARB compressor has)? like a .5-1 gallon tank w/water trap and an ARB switch... then run that to a distribution block where you could run a line to the back of the rig and a 5 gallon portable tank with a ball valve and quick-chuck?

Post by **maybs** » Sun Jan 07, 2007 9:57 pm

I just read a write-up about using the stock AC compressor for OBA. There was an interesting tidbit in it about using hollow bumpers as an air storage tank. Seems like a great idea, but you would probably want to air them down when driving, to avoid explosions if you ram your bumper into something while it is pressurized.

Post by **yotacowboy** » Sun Jan 07, 2007 10:26 pm

if by "explosion" you mean a loud whoooosh noise, you're right... otherwise 90-120 psi in a steel bumper ain't gonna do much if the bumper is breached.

Post by **Steinberg** » Sun Jan 07, 2007 10:46 pm

150psi in sch40 pipe is about as dangerous as a balloon. it's an option I've had in the back of my mind, but I'd prefer to have a dedicated tank. the more I think about it the less I am worried about sometimes operating without a tank. the volume inside the lines between the compressor and the bed of the truck should be enough for some "buffer", and if not the relief valve will let off the extra.

one thing I know I will need is lubrication for the compressor. so an oil mister upstream of the compressor and a coalescing filter (oil remover) downstream will be required. the coalescing filters are expensive (the cheapest I've found so far is $50). I have read that the simple oil/water separators are insufficient.

I'm planning to pull air from the filtered side of the existing airbox (upstream of the mass air flow sensor), rather than have a small filter exposed to mud and water in the engine bay. I will probably make a custom manifold out of some scrap aluminum to bolt onto the AC compressor and mount most of the widgets.

Lubricator: $25
Coalescing filter w/ steel bowl: $55
Pressure switch: $20-$35
Relief valve: $5
Check valve: $10
Hose, fittings, couplers, quick disco's, etc: $30-50?
Porta-tank: $35

so ballpark cost could be $180-215 when it's all said and done. Reasonable.

Time to go liberate some freon.

Post by **Steinberg** » Sun Feb 11, 2007 4:22 pm

I finished this project finally.

This is the manifold I made to bolt onto the AC compressor which has o-ring face seals. The other side of the manifold is threaded for 1/4" NPT fittings.

This is a compact distribution block I made.

I ran copper tube between the compressor and distro block to dissipate some of the heat from the compressed air. There is an oiler at the compressor inlet, and a coalescing filter for de-oiling at the distro block. The filter has an auto-drain, so I'll be able to make it recycle the oil back into the oiler. Also in there is a check valve, 90/120 pressure switch, and safety pop valve (150psi).

Clean air from the airbox.

In the back mounted under the basket. the second orange line goes to the porta-tank. It's got a valve and quick disconnect at the block there, so it can be popped right on and off. The regulator is downstream of the tank.

Post by **BlueDodgeRam** » Sun Feb 11, 2007 6:25 pm

that looks nice, good job

Post by **VerticalTRX** » Sun Feb 11, 2007 9:20 pm

The one thing that a tank gives you is more CFM volume for short bursts. Some air tools take a ton of CFM, and I'm not sure what an AC compressor moves, but I doubt its enough to keep up with some air tools. With a tank plumbed in, even if its only a 5 or so gal one it will give the air tool a nice big burst of CFM and PSI for a short while (like an impact breaking free a bolt), then the compressor will have time to catch up and refill the tank. If its mostly for filling tires and such no tank would probably be fine, but if you plan on running tools I'd have a minimum of a 5 gal tank. Maybe I'm wrong about this (never done OBA), but from my experiences with other pneumatic setups this will be the case.

Post by **Steinberg** » Sun Feb 11, 2007 10:57 pm

I agree Matt, which is why I included the 11gal porta-tank in my setup. From what I've heard, the AC compressor will push enough CFM to run an impact gun, especially if you give the engine some rpms, but I'd still rather have the tank there so that the pressure doesn't fluctuate as much and the compressor does not cycle as frequently. At idle speed, it aired up my mostly-flat Q78 in less than a minute, without the help of the tank.

Post by **VerticalTRX** » Mon Feb 12, 2007 10:47 am

Piney wrote:....which is why I included the 11gal porta-tank in my setup. .

I must have missed that somewhere. :lol2:

Post by **hssss** » Sat Feb 24, 2007 4:22 am

I have a couple of medical "E" bottles that you might be able to use with a shutoff valve and a quick disconect. What I've put together for My Jeep BJ is to use the York compressor which was mounted to the 460 in it from that a seperator to pull oil out then an old A/C condenser another seperator to pull out water a 125/175(?) controller which will have a line from the bottom of the second seperator to the relief valve to automaticly dump the condensation then a 200 (?) check valve to a manifold and two aluminum medical "E" bottles. The quick disco is a good idea.
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Dodge 330 Specifications

Post by **Steinberg** » Sun Feb 25, 2007 2:58 am

hssss wrote:I have a couple of medical "E" bottles that you might be able to use with a shutoff valve and a quick disconect. What I've put together for My Jeep BJ is to use the York compressor which was mounted to the 460 in it from that a seperator to pull oil out then an old A/C condenser another seperator to pull out water a 125/175(?) controller which will have a line from the bottom of the second seperator to the relief valve to automaticly dump the condensation then a 200 (?) check valve to a manifold and two aluminum medical "E" bottles. The quick disco is a good idea.

what size are these medical bottles? the porta-tank seems to be working good, although I had to return the first one I bought cause the safety valve was popping well below the 125 psi max pressure. the one i have now doesn't pop, but the gage "sticks" a little bit. overall I'm real happy with the system. I need to add a hand-throttle type deal so I can up the rpms to get some more CFM, but even at idle it seems to push plenty air.

it runs my IR impact gun pretty well. I need to up the regulator above 90psi for this cause i think i'm losing a bit of pressure going through the cheapo coiled hose. i only got the regulator cause i was worried about over-powering the airtools, but maybe at 90/120 system pressure and the pressure drop due to 25' of coiled hose it's not necessary after all. meh, the reg. only cost $20.