Locating ARB compressor in the rear (and other rabbit holes related to on board air)

[kcjaz]

I’m pretty sure filling 4 tires in parallel will take the same amount of time as filling them in series in terms of the compressor running time. Think of it this way, if you have a compressor with a 2 gal air tank and it takes 1 minute to fill and you change the tank to 8 gal, it will now take 4 minutes to fill. In each case, the CFM rate will be the same if the only difference in the system is the volume of the tank.

Regarding the Schrader valves, they are a restriction, that what valves are. Having a larger valve would allow filling and deflating faster. The rapid deflate things that pull the stem out demonstrate this. The Power Tank guys sometimes add a second big a$$ fill valve so they are not limited by the small schrader valve and then can fill there 37s in a minute.

 

[Oakleyguy]

Doesn’t the compressor sit snd cycle against its pressure limit switch in applications with air lockers? Waaayyy less duty cycle then.. but much higher pressure than tire filling.

Having thought about this only a small amount, I am inclined to believe it is more the heat from under hood installs that kills them. But this is just my gut. And why I have a process to try and cool the compressor down a bit before filling tires.

Also a single air line takes up enough room in my camping/roadtrip setup.. I wouldn’t want to add so much extra hose to do the same job.

Adding further, my compressor has lived under hood the last five years and works like a charm. I believe the heat from the engine bay is minimal compared to the heat the compressor produces itself. I measured my arb singles manifold temp at 210degF on average after five minutes of run time.

regarding space, on my setup my hoses whips take
up roughly the same amount of space for a longer single hose. I’m running four 6’ whips. But space management is very much a personal preference.

 

[kcjaz]

Thanks all. My conceptual plan is to put the ARB compressor under the hood, the ARB hard switch in the cab but also add the compressor to my Warn Palatium wireless controller as I already have that (I originally thought adding accessories to that was a little silly but it should be easy and might be useful at times). I will put couplers front and rear and make a DYI "4-flate" system. Since I'm not really capable of original thought, I will copy much of what you guys have done on your rigs. My tweak would be to make my "4-flate" essentially from two "bi-flate" systems and connect each to my "air header" at the front and back. Kinda like @Oakleyguy's system with couplers at the 4 corners but using only 2 couplers. Having an "air header" running the length of the vehicle will save some coiled and stored hose length.

For those running air lines to the rear, are you just using regular air hose or is any one hard tubing or using braided hose? I was planning on using Flexzilla hose for the whips and was just thinking of using the same to run the line back to the rear and front couplings. Not sure how Flexzilla will stand up permanently installed in the engine bay. Maybe need to do something different there.

 

[kcjaz]

ARB specs for reference:

note that 100% duty cycle rating for the CKMTA12 is at 72F. Underhood will a little warmer...

Found this too as I was contemplating hose size and general air system design. (way past rabbit hole here and am now digging with worms).

 

[bloc]

Someone mentioned in the compressor/lifepo thread that having spare fuses for the ARB is a good idea. Somehow this hadn't occurred to me..

Figured it was worth mentioning here in case anyone else had the same brain fart. 40A Maxi-fuse, 2 needed for a twin.

 

[kcjaz]

Further down the hole:

So, the ARB twin is rated at 4.68 cfm at 29 PSI. Assuming they use 72F in as a basis for the 4.68 cfm, at 180F (engine bay ambient??) this would reduce that by about 20% and add a little more for not being at sea level and the compressor is probably putting out 3.5 CFM. Converting 3.5 CFM to SCFM and running a random air flow calculator found on the internet, I come up with the table above for pressure drop per 10' section of hose. My conclusion is what I think I already knew, 1/4" ID hose results in a restriction that I think would be noticeable in terms of time to inflate your tires. 3/8" is probably a good choice if you don't like the extra bulk of 1/2" hose.

Please feel free to point out the math errors or bad assumptions I have likely made.

 

[Oakleyguy]

I am running 3/8" ID air brake tubing in my setup.

 

[Oakleyguy]

Adding further, @kcjaz PM me if you want a copy of my custom bracket in the wheel wheel.

 

[1world1love]

I ran something like this to the rear:

Amazon product ASIN B08K2TNSVK
It was easy to work with and has held up. I did wrap it in split loom for extra protection. The hose that I used was approximately 3/8 ID (mm spec). My compressor only puts out about 2.5 CFM at 0 so this size seemed fine and has worked fine.

I have the same model compressor in portable format and the fill time is the same for both compressors using my morflate, either directly connected for my portable, or through the rear disconnect using my onboard, so I assume the pressure loss is negligible.

 

[bloc]

Further down the hole:

View attachment 2760517

So, the ARB twin is rated at 4.68 cfm at 29 PSI. Assuming they use 72F in as a basis for the 4.68 cfm, at 180F (engine bay ambient??) this would reduce that by about 20% and add a little more for not being at sea level and the compressor is probably putting out 3.5 CFM. Converting 3.5 CFM to SCFM and running a random air flow calculator found on the internet, I come up with the table above for pressure drop per 10' section of hose. My conclusion is what I think I already knew, 1/4" ID hose results in a restriction that I think would be noticeable in terms of time to inflate your tires. 3/8" is probably a good choice if you don't like the extra bulk of 1/2" hose.

Please feel free to point out the math errors or bad assumptions I have likely made.

Keep in mind only the line off the pump and manifold will be full-flow for inflating. As things split to different parts of the truck less flow capacity is needed per line.
3/8” to the bumpers, split to 1/4 from there?

 

[kcjaz]

Keep in mind only the line off the pump and manifold will be full-flow for inflating. As things split to different parts of the truck less flow capacity is needed per line.
3/8” to the bumpers, split to 1/4 from there?

Yes. My initial thought of feeding the front from one connection and the real from another means ~1/2 of the total flow to each end. Still, I would be incliuned to just stay 3/8" in all of the drops. I don't think there is a lot of cost savings to neck down to 1/4". Storing 4 short 1/4" whips might be better from a storage space point of view but I'm not too worried about that. I also want to use the system for 4 tire deflation where the flows would add up depending on where I put the vent and when deflating, the pressure drop would affect the time more.

On a side note, I have also thought about adding an air tank but I don't really see any advantage for a 1 or maybe 2 gallon tank given a 4 cfm compressor used for tire inflation. I haven't done the math on how may tires a 1 gallon tank at 150 psi could inflate but I don't think that wouldn't even refill one tire back to 40 psi. I think you would need a 20 gallon tank to do much good. I don't really get the benefit of the ARB 1 gallon tank. If you could fill a bunch of tires with a 1 gallon air tank, no one would by a CO2 Power Tank.

 

[1world1love]

Yes. My initial thought of feeding the front from one connection and the real from another means ~1/2 of the total flow to each end. Still, I would be incliuned to just stay 3/8" in all of the drops. I don't think there is a lot of cost savings to neck down to 1/4". Storing 4 short 1/4" whips might be better from a storage space point of view but I'm not too worried about that. I also want to use the system for 4 tire deflation where the flows would add up depending on where I put the vent and when deflating, the pressure drop would affect the time more.

On a side note, I have also thought about adding an air tank but I don't really see any advantage for a 1 or maybe 2 gallon tank given a 4 cfm compressor used for tire inflation. I haven't done the math on how may tires a 1 gallon tank at 150 psi could inflate but I don't think that wouldn't even refill one tire back to 40 psi. I think you would need a 20 gallon tank to do much good. I don't really get the benefit of the ARB 1 gallon tank. If you could fill a bunch of tires with a 1 gallon air tank, no one would by a CO2 Power Tank.

There is a thread with a nice discussion on the question of tank or no tank. I will see if I can dig it up, but @TeCKis300 I think went through this equation and the general premise is that for small tanks, it might not make sense unless you were using an air tool or possibly air lockers.

 

[kcjaz]

There is a thread with a nice discussion on the question of tank or no tank. I will see if I can dig it up, but @TeCKis300 I think went through this equation and the general premise is that for small tanks, it might not make sense unless you were using an air tool or possibly air lockers.

I'll search for the thread. I wasn't thinking about air lockers. Maybe it would make locker work a little better by having enough volume in the tank to actuate them such that you could hit the button and the compressor wouldn't have to come on at exactly the same time. Don't know how much air a locker actually uses but if it is more than the little manifold holds and less than the 1 gal tank. The tank might make sense. So next question is do people with air lockers add little tanks?

 

[bloc]

The arb manifold is usually more than enough for air lockers, and that is why the solenoids attach directly to it. We’re talking the volume of the lines and a very small actuator space inside the carrier assembly.

Now if you have a leak somewhere.. but a bigger tank will eventually be limited by the cfm of the compressor anyway.

 

[kcjaz]

The arb manifold is usually more than enough for air lockers, and that is why the solenoids attach directly to it. We’re talking the volume of the lines and a very small actuator space inside the carrier assembly.

Now if you have a leak somewhere.. but a bigger tank will eventually be limited by the cfm of the compressor anyway.

So maybe with a tank you could go in and out of locked a few or several times without cycling your compressor but really, so what? By the time you get over whatever you hit the locker for the manifold would be charged again to 150 psi.

 

[bloc]

So maybe with a tank you could go in and out of locked a few or several times without cycling your compressor but really, so what? By the time you get over whatever you hit the locker for the manifold would be charged again to 150 psi.

Exactly.

 

[kcjaz]

Started install. I’ve moved the air pump relays using the Slee bracket but am wondering if I’m miss understanding which fuse box bolt to mount the bracket on. If this right?

the Slee bracket is very close to the break lines and because the bracket only has one mounting bolt on the fender, it can bounce with vibration. I’m a little concerned it might wear on the break line tubing.

 

[kcjaz]

So I decided the location of the air pum
Relays was “correct”. After reading about issues with worn wires due to contact with the brackets I paid attention to that and pushed the relays as far to the outside as possible and angled the bracket as much as I could to limit contact with the break lines. I thought about widening the slot in the bracket but didn’t. All wires look ok.

I de used to just mount the switch under the hood in the slot for it on the Slee bracket. This was just easier for now. I just wanted to get the thing installed and running. I’ll use it like this for now and add front and rear air chucks later.

I did one test and it took 1:18 to fill one time from 20 to 40 psi. That’s about 5 times faster than my old compressor so pretty happy with that.