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On board air and storage questions

B

blistovmhz

NAXJA Forum User
Location
Vancouver, BC
Couple questions regarding OBA that perhaps someone already has answers to.

Setup:
Intake = Air box > inline oiler > compressor.
Output = Compressor > standard air hose > oil filter > manifold (pressure switch, gauge, blow off, 2x output to tanks (sliders), 1x output to air hose)
Tanks/sliders = 2x6x72" 3/16" steel tube, seam welded. (864ci or 14L each. 28L combined)
Tires = 35x12.5r15 (140L total volume)

Problems/questions:
1. Heat
I can fill up the tanks to 100psi in about 60 seconds but I'm running into a heat problem at the compressor. My output line is melting and popping usually after around 7 tires (35-37" tires).
Is the heat indicative of insufficient oiling, too high RPM, too high duty cycle, or do I need to run a copper coil on the output? I've heard of other guys having this issue, but never seen a good solution with follow up.

2. Pressure ratings
I won't bore everyone with the math, but ultimately to get my tanks to fill up a single tire from flat to 25psi (my street pressure) I need 125psi in the tanks. I figure I might as well figure out exactly how much pressure my rectangle tube can deal with (assuming all my welds are sound). I've looked all over and haven't found a definitive answer. Some guys say that running anything over 75psi will deform the metal in a hurry, while other guys say they run 300psi. I feel like I should be able to run 150-200psi pretty safely but I'm hoping someone who actually KNOWS can chime in here. It'd be awesome to be able to fill up two tires from flat, without the compressor turning on.

3. Duty cycle
I've heard that the AC compressor can easily move 4.5CFM at 100psi at 100% duty. Is this true?
As stated in question 1, after 7 tires, I almost always blow out my high pressure hose. I'm a bit worried that the heat may be killing my compressor. Anyone run an AC comp based OBA for a fairly long time, and have any input? I have several spare compressors, but it sure would be annoying to lose my compressor on the trail when I've got an hour of highway to get home with 7psi :)
 
Kingkong0192 said:
Is this a sanden or a York
Setup?

I'd also put an oil seperator on the output side to ensure that your air is actually clean air.
Click to expand...

Sanden, and there is an oil separator on the output.

Talyn said:
1) Run a length of stainless steel line from the compressor to the standard air hose.
Click to expand...

Will this really be enough cooling? I was considering doing this but wanted to hear from other guys who've already solved the problem. How much steel line do I need to provide sufficient cooling? Should I run a coil like I'd originally intended, or is a couple inches going to be enough?
 
For the heat problem I just used the factory line with rubber hose section. I connected my air hose to a section of metal tubing passed the rubber section. I've air up several rigs in a row, no problems.
 
hackedxj said:
For the heat problem I just used the factory line with rubber hose section. I connected my air hose to a section of metal tubing passed the rubber section. I've air up several rigs in a row, no problems.
Click to expand...

I sorta get the feeling then that my AC compressor is just overheating for some reason. I used a chunk of 1/2" power steering hose for the HP side this time and it popped as well (at around 90psi on the 7th tire again).

Wait, what RPM are you running when filling up tires?
 
Ac hose is designed for the heat output, the compressor will melt hose (i.e. standard air hose) not designed for the amount of heat generated by a ac compressor.

I have a similiar set up but I made a copper cooling coil that comes off the AC compressor then goes into plastic airbrake tubing (less heat tolerant than rubber air hose)

The copper pipe is the same diameter as my air brake hose (i used 1/2") comes off the compressor and is formed into a coil that has the same inner diameter as the diameter of the AC compressor. It makes about 4 coils before exiting into the air brake tubing. Having the copper formed in a coil makes the air cool down faster than having it straight as the air is forced against the inner walls of the copper which removes the heat very efficiently.
 
I run a York 210 compressor with only 6" of 1/2" copper pipe with a 90° bend before going into 3/8" I.D. hose. There is about 1ft of hose before it hits the one way valve and the oil filter. The goal is to give the air plenty of time to cool before being restricted. I have run this system for years and filled multiple tires with no down time with no issues.

The system also has a 1.75g tank and the pressure switch runs 90-125 psi. The compressor runs pretty consistent while filling my 35" tires.
 
You can use a Viair 92791 stainless hose off the back of the compressor as well. It also has a built in check valve. I found out about this from googling oba setups a while back. Should run about 30 bucks on Amazon. A Viair 90100 switch that turns on at 90 and off at 125 psi seems to be the perfect pressures.
 
blubullett said:
How many tires do you have? My xj only has 4. So fill yours up first and if the line blows then the unprepared person can go home with 7 psi.
Click to expand...

:) I generally go out with at least one other truck every time, and I happen to have the fastest pump. Either way though, I'd like my pump to NOT blow up, regardless how many tires I need to fill up. I don't like knowing that my pump is only 5 minutes away from stranding me on the trail.
 
blistovmhz said:
Will this really be enough cooling?
Click to expand...
Nope, but thats why nearly ever after market compressor worth its weight has a length of stainless line.. because the temp won't melt the shitty air line.
blubullett said:
How many tires do you have? My xj only has 4. So fill yours up first and if the line blows then the unprepared person can go home with 7 psi.
Click to expand...
That nice. Why are you here?
 
I use a cooling coil made from 10' of 3/8" copper line wound around a spray paint can. cooled the air charge well enough, but underhood temps would still melt the truck brake line. ended up replacing it with stainless
 
Well, I found some 3/8 copper tube (10') and wound it up over a spray can. Hooked it up and it seems to be working. I haven't run the pump long enough to be sure if this solves the heat issue, but by the end of one tire, the side of the coil connected to the AC pump is definitely hot and the other end is cold. :) Woot Woot!
 
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