Northwoods Snowman

So I've been trying to do some more research/planning for an OBA system. I have a York 210 compressor but am trying to determine if I need a tank or not, and how big of one if I do. I see on the Kilby website and some others (mostly forums referencing the Kilby site) where the "advertised" CFM rating of the york is 4 CFM at 90 psig at 1,200 RPM. I'm calling BS on this. I run the calculations from my fluid mechanics book and at 90 psig the pump is capable of 1.0 CFM at 1,200 RPM without any losses. Since air volume is proportional to pressure, 90 psig (104.7 psia) is approximately 7 times atmospheric pressure (14.7 psi). That means that the air has to be compressed to approx. 1/7th it's original volume. You can do the math if you want, but a 10.3 cubic inch displacement compressor works out to 7.15 CFM at 0 psig at 1200 RPM. Times that by 14.7/(90+14.7) and you get 1.0 CFM at 90 psig. I don't know where the heck they get 4.0! Maybe one of you guys can enlighten me? Is there something in the conversion for SCFM values that I'm missing?

So, I mostly want the system to be able to air up tires. It would be nice also to have the capability to run air tools like an impact. I know I could run without a tank to air up tires, but what about run tools? If I were to try to run a tool with the values I'm calculating it ain't going to work. I don't think I would even be able to build up 90 psi to run the tool. Has anyone tried this? I'm thinking maybe I should be deferring to real world experiences instead of text book calculations. If I'm correct in thinking I would need a tank to run air tools how large of one would I need? I know the tank isn't needed for duty cycle as the compressor can run 100% but I don't know how much system volume I need to be able to maintain pressure around 90 psi.

TheCodeMonk

The real reason for the tank is so you don't wear out the pump. The pump may be capable of pushing the air you need but if you hook directly up, it will always be cycling on and off (esspecially with air tools) rather than just running a while to fill up a tank, then staying off until the tank is below a certain threshold.

SeriousOffroad

Yes you should a run a tank in your system. The tank gives you the volume you need to quickly air up tires, and air tools.

Northwoods Snowman

I'm not worried about wearing out one of these compressors, they can run 100% duty cycle (and I wouldn't be running for hours on end lol). I see what you're saying about cycling on and off. I would think that would be more of an issue if the compressor has excess capacity than the tool requires. I.E. the thing pumps up to max pressure, turns off and then the pressure immediately drops so it turns back on. I guess I'm trying to establish if the York has the excess capacity or if it would be running 100% of the time a tool was on trying to keep up with it. See what I'm saying? I see where a tank would be helpful in either situation though, the question then is (especially if the compressor is underrated) how big of a tank is required? I've seen you tube videos of these filling 8-10 gal tanks to over 100 psi in around 60 seconds so I know they can put out some air, which doesn't seem to add up with my 1.0 CFM calculation.

How much advantage does the tank give you for the tires? With out a tank the tire essentially becomes the tank you're filling and from what I calculated it's putting out 2.02 CFM at 35 psi. Do you have a tank size recommendation for the system I'm trying to put together?

slk88cherokee

Yes use a tank. Just because it says 100% duty that doesn't mean its good to run it like that. If you plan to run air tools you need volume and pressure and having reserve makes life so much better on the compressor clutch. That math thing looks really cool by the way. Do you plan to use the comp or just do the engineer equation until it sounds good. Lol...sorry had to say it! My best friend is a mechanical engineer and pisses me off daily with his math crap and is usually not even close to real word numbers. He does this big math thing and I say just hit it with a hammer it'll fit! Yes use a tank you will be way happier and they're like 30 bucks for a 1-2 gallon

SeriousOffroad

A huge advantage since the tank is holding a larger volume.

An on board air system should include all of the same components found on any decent home/shop air compressor.
Compressopr
Tank
Pressure relief
Unloader with integrated pressure switch for cycling the compressor.
Oil Seperator w/oil return line

peep

Plumb in an air pig (about 4 gal tank) available at most local auto parts and tools hardware stores. Plumb it in with a t-fitting to give you the reserve capacity you'll need. Tires, the primary reason for the air. How many air tools are u really planning to carry? I take my home electric impact that I can run off the inverter. Only ever used it once by necessity over the breaker bar in tight to ground clearance hole when no other choice since I didn't have room to swing the breaker bar. Have also for changing tires but that was convenience over necessity. The air however was a godsend when on fourth tire plug fix in one day on most frustrating trail ever north of Havelock. Trail was sabotaged!
So bottom line is a small air pig will work great hooked on line with your onboard air con compresor conversion.

Northwoods Snowman

I guess the only real air tool I would be looking to use would be in impact for pulling the wheels off. Seem about every time I run through any amount of mud I have to adjust the rear brakes up and it would be nice to easily pull the drums off and clean the crap out before adjusting them for the trip home.

Seems pretty unanimous that it's a bad idea to run without a tank. So back to how big of a tank is really needed? Are you running a York 210? How large of a tank are you using and how often is the compressor having to run? I've seen 1-2 gal (where would I find one of these for the $30 mentioned?) and 4 gal mentioned so far.

I'd like to be able to keep the tank outside the passenger compartment because cargo space inside is typically at a premium so mounting location suggestions would be appreciated too. I don't have bumpers and the best spot I've found so far is forward of the rear axle and left of the drive shaft. If I remember I can fit about a 12" by 6" tank there fairly easily which would work out to about 1 gal but not sure if that's going to be sufficient.

Northwoods Snowman

So... no further recommendations on tanks?

favaguitars

A quality 18v hex drive impact will suit your needs much better. Two or three batteries is all you will need. I can do a motor swap on one battery.

Northwoods Snowman

Totally wrong thread, lol. Not sure where you meant to put that.