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I've avoided designing my onboard air system until now, but am having second thoughts about waiting until the interior is more built out. Seems like running wires and air lines might be easier now than when the walls and cabinets are in. My goals are:

-Remotely control the airbags (up or down) from the dash to be able to level the van at campsites, get extra lift when going offroad, maintain airbag pressure for road/load conditions)
-Refill the van tires after airing down for off-road (30/45 PSI to 55/75PSI)
-Blow out dust and sand from the van interior, dry the dog, quick dry things

-Idea is to have a central tank (2.5 - 5 gallons) under the chassis in the rear in front of my spare tire (tons of room on my extended).

-I'll run some quick connect air fittings from the tank to both sides of the van and possibly the rear bumper, and one inside, in order to be able to fill up the van tires, bike tires, and inflatables (tubes, air mattresses, etc).

-I'll have Airlift 5000 Ultimate bags in the rear. Planning on having a manual control for them up in the dash using this:

-The air manifold will just hook in to the bags and tank (with pressure regulator).

-Tank will have a pressure switch to turn the compressor on when it gets below a certain value. I'll probably try to wire up an air pressure gauge to the tank itself that is a sending unit to my Victron Cerbo GX so I can check tank pressures. Finally, I'll have an on/off switch for the compressor, either in the dash or in the back, to cut power to the compressors (I won't keep it on or the tanks full most of the time.)

The one piece of the puzzle I'm still trying to figure out is what compressor setup to run. I don't really want the compressor inside the van.
I pretty much want 100% duty cycle.

ARB Twin Compressor (CKMTA12): $600, 4.68 CFM @30PSI, 150 PSI Max, 70A current draw. Only IP55 rated, which is the main problem. I don't really think it's a good idea to mount it under the van. I could try to create a mostly water/splashproof box and use an air intake relocate kit into the interior of the van, but that's a decent amount of effort. I was thinking about trying to mount it in front of the driver side wheel in the bumper (same spot as the windshield fluid reservoir, just opposite side. Should be pretty protected and have good air with the front wheel liners installed. Problem with that is running the power wires for 70A over to CCP2 inside the cab - needs pretty thick wires and that space is already too crowded with my audio install. Running super thick gauge wire to the back passenger side of the van where my house electrical is seems a non-starter.

Viair 485C Compressor: $400, 1.67 CFM @30PSI, 1.36 CFM @80PSI. .
200 PSI Max, 23A current draw, IP67 Rated, 100% Duty cycle at 200 PSI.
Could mount this under the chassis no problem, wiring would be pretty easy and straightforward. But the fill rate seems low? Says 5.25 min to go from 0-30 PSI on a 37" tire, 1.5 min to go from 15-30 PSI. No clue what that means from going from 45-75PSI, but I'd assume it would take slower (6 min a tire?)

Viair 485C Dual Compressors: $525, 3.05 CFM @30PSI, 2.34 CFM @80PSI.
200 PSI Max, 44A current draw, IP67 Rated, 100% Duty cycle at 200 PSI.
Enough space under the chassis as well. Says 3.75 min to go from 0-30 PSI on a 37" tire, 1.8 min to go from 15-30 PSI.

Anyways, just trying to figure out what I actually need. Seems like most people have compressors considerably less powerful than these (like Viair 88P, 1.25 CFM at 30PSI, .75 CFM at 80PSI, only 25min Duty cycle at 30 PSI)? Seems like this is not nearly adequate to get the van from air-down pressures back up to Highway pressures? Am I missing something?
I've been very happy with the Viair 400P, which is popular with off roaders for good reason. I got the automatic version and I'm glad I did. Was like $220 new on an ebay competitor site. I thought about mounting it underneath but it's too dirty down there, so I usually just pack it. It's very easy to setup; 1-2 minutes tops, and always clean as a whistle inside it's carry case. I rigged up a fused always hot connection to CCP2 that sits right there by the open driver's door. I use it often. More about that here.

But so far I don't have air bag plans, or really need compressed air for anything. The factory rake plus the VC lift kit (no bilsteins up front) have made it so that even with most of my big ticket heavy items installed the rear is still higher than the front, so rear airbags would only make it worse (that annoying ~80mph drone sound is gone though). I typically park with the front facing uphill to help overcome this. When on level ground or if I can't face uphill, I can press just the head lift button on my adjustable bed remote for a second. But that only buys about 1-2" before it starts to feel awkward at the hip/chest area while sleeping, and I have to remember to do it every night. A little side to side tilt isn't a huge deal because the bed faces front to back, but I guess it would be nice to be perfectly level on that axis. I just can't tell if air bags and all the gear to make them work are worth the effort. Here's a shot of the adjustable before I put the mattress on. I friggin love this thing. Have used one at home for decades.
Couch Furniture Comfort Wood studio couch

For people with side to side beds, I could see air bags being more useful, but again, with a VC lift and no Bilstein's, you might have a rake even after your build is complete, so airing up either rear bag would make it worse, which might cause you to roll out of your bed, or be at a diagonal. You can build your bed platform to lean towards the back, but it would need to over-lean beyond level and then you'd need to air up both bags by some amount every time, otherwise just using one bag would again create a diagonal or forward lean/roll.

I've read a few people on the forum say they won't drive with the bags inflated anymore. Not sure what that's all about, but might be worth looking into.

Anyhow with the 400P Automatic I have no problems airing down and back up without interruption even on hot days. The automatic stops itself between tire fills, and I usually only drop 5-10 PSI even for thick sand and gnarly death valley jeep trails and just skip filling back up on the way out. If you air down too far, you start giving up ground clearance, which is a bigger issue on most of the rough roads I take, even with 265/75/16's.

The factory PSI ratings on the van are also very high because they have to cover even heavily loaded rigs, and while my build has a massive power system, it's still not heavy enough that 5 PSI matters, yet that's usually all it takes to trim the edge off of the ride harshness and improve traction a bit. I've been through insanely thick sand like that without any issues. Just gotta keep a bit of momentum. You can go much slower if you really air down but then you definitely need to stop and fill up on the way out, and again, you lose some ground clearance.

I find I'm usually not in the mood to pull over to refill after I get off the jeep trail and back onto the nearest highway...something about craving a burger, or just looking forward to getting to my next stop. Hard to say why exactly, but my brother is the same way. When it's time to go, it's time to go.

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