The 70 amp relays are EASY to find, they are all over E-bay and else where.
About all the HID lighting systems on the upscale cars use them,
They are used for power seats, and other stuff all over common cars.
In a pinch, you can walk in and pick out a 'Starter Relay' for a Harley Davidson and they will hand you a 70 amp automotive relay just like the ones I've been advocating for electric compressors.
Hella lighting systems for off road vehicles uses the same 70 amp relay as Harley and most BMW, Lexus, Cadillac and about everything else that uses HID lighting.
The flexible 'Whip' hose from compressor to plumbing system is there to...
1. STOP line breakage because of engine vibration.
Flexible hose doesn't fracture like hard line when connected to a vibration producing mount.
2. To allow the discharge air, which can be close to 200 degrees, to cool some before it hits plastic fittings.
There is plastic/rubber in EVERY swivel fitting, There are tons of fittings with plastic seals & liners, so just because it LOOKS like it's all metal doesn't mean a thing.
Whips run about $20, and for me they are pretty much MANDATORY,
But don't take my word for it, I only do this every day, all day long for a living
Proper DC compressor switches are about $20 each...
I carry three common kinds at work,
On/Off pressures, 90/120, 130/135, and 135/150.
The 90/120 is the most common for vehicle install and it works FLAWLESSLY.
Since most engine driven compressors are going to spit oil, DO NOT expect the 'Pump House' or 'Water Tank' switch to last long.
The oil will rot the seals very quickly, and you are out looking for another $40 or $50 switch in no time.
Plus, they are big and ugly and not rated for DC current switching.
All of which have been problems for us in the past,
So we use a CHEMICAL RATED, DC RATED, Actual COMPRESSOR SWITCH.
Not some 'Monkey Rigged' water pump switch...
DO NOT worry about 120 PSI of air pressure 'BLOWING UP'...
It won't happen, you get a 'Woosh' of air if you puncture the tank and that's about it. No 'Explosion', no 'Shrapnel', none of the horror stories, there simply isn't enough pressure/volume in these little tanks to do the things you hear about...
I've popped a couple of tanks on the trail, so I'd advise keeping away from the 'Shiny' aluminum tanks if you actually wheel your Jeep... they get punctured pretty easily compared to the steel DOT rated tanks.
The best place to get a 'Low Budget' tank is a big truck parts store.
They are heavy gauge steel, rated for a working pressure of 150 PSI, and stress tested to 3 times that amount to pass DOT regulations.
A big truck salvage yard will provide you with all the fittings, hose, tanks, switches, air manifolds, relays, ect. you can carry away for cheap,
And you will find tanks in all shapes, sizes, volumes, mounting arrangments, ect.
Since the 'Average' big truck has about 5 tanks, and the average trailer has 3 tanks, they are EVERYWHERE in a salvage yard...
You will get DOT rated hose, fittings, switches, tanks, ect., Not the 'Made In China' crap a lot of the 'Off Road' places are trying to sell as 'Kits'...
If you go with an engine driven compressor, try to make it a York.
The largest volume compressors York made with a DC clutch was for Ford/Sterling big trucks, and you can find them in International trucks also.
MUCH larger displacement than the Jeep/York most people use in this situation, and the mounting flanges on the big truck compressors are EXACTLY the same as your Jeep brackets...
MAKING your own manifold for your SPECIFIC application can be a good thing.
I saw a guy make an 'Inline' manifold out of a 'Turn Buckle',
Re-threaded the ends for air line fittings,
Drilled/tapped holes in the side for his appliances, and since it was aluminum, it looked nice and dissipated heat quite well.
Another solution is a plain aluminum block. Anything you can find about 1" square bar to about 1" thick and 3" square will make a GREAT manifold.
Since you are working with AIR, The passages do NOT have to line up 'Exactly'...
As long as the air can pass through, it's no big deal, so a hand drill is FINE for the work.
Tapping the holes isn't any big deal once you have done it a couple of times and use good lubrication on the tap...
Just remember to back out/break chips OFTEN, and use the correct size drill bit to begin with...
Hand drill, some drill bits, a hand tap and a vice to hold it in is about all it takes.
If you are working with Aluminum, Copper or Brass/Bronze, just make SURE you use a proper cutting/tapping lubricant and back out/break chips early and often.
This takes NO specialized tools, nothing expensive, and nothing hard to do,
Just time and practice.
DO NOT BUY 'CHEAP' TAPS! Get good CARBON steel taps that are sharp!
Cheap taps will cause problems, and high speed steel taps like to break without warning and are a pain to remove!
You can break a carbon steel tap with a sharp chisel if you break it off in the hole most times...
Carbon steel stays sharp longer, and that is a GOOD THING!
Taps are usually under $20, and some come with the proper size drill for the tap for a few extra bucks if you don't have a good set of properly sized drills...
On Board Air is VERY handy to have,
And the more tank space you have the better off you are!
Two or three small tanks equals one LARGE tank!
This is AIR you are pushing around, so you don't have to worry about fluid flow or anything else, just plum them together anywhere you can get them mounted and they WILL work together....
Most people think they have to run one hose INTO the tank, and a separate hose OUT of the tank to the appliance.
Nothing could be further from the truth!
The same line that feeds the tank can have a 'T' in it for you to use air right off of, or go to a second or third tank... and they will ALL contribute to total volume, and will all equally combine to power anything you want to do...
Air doesn't care where you put it into the tank, take it out of the tank, or combine more than one tank to do the work...
No 'Gravity' feeding like you have to do with liquids, it can all work off ONE line with no issues.
As for the pressurized drive train questions...
Once you have gone through a pressure regulator,
You can pressurize ANYTHING that has a vent in it.
The Differential housings on the axles are a prime example,
So is the transmission/transfer case.
Since EVERY COMPONENT HAS SEALS in it, the excess pressure will escape through those seals...
My axle tubes blow bubbles under water. The pressure isn't excessive enough to blow the seals out,
And SOME air escapes past flaws in the seals.
Those bubbles tell you that you WOULD have had water in the housing because of those flaws in the seals!
My transmission blows bubbles around the shifter arm.
Again, the pressure isn't high enough to dislodge seals,
Yet any escaping air shows you where water WOULD HAVE ENTERED without the pressure...
The problem with the transmission is,
The transmission was TOO LEAKY to pressurize!
People seem surprised to find water in their transmissions after leaving the Jeep out with the top off...
They seem so surprised when I show them you can pour water on the shifter and it runs RIGHT INTO THE TRANSMISSION!
That shifter arm leak is so bad I couldn't keep enough air VOLUME in the system to get pressure.
I had to use an ATV CV joint boot, hose clamp it to the transmission pivot pin mount on the top cover of the transmission,
And run the shifter out the 'Little Hole' in the CV joint boot and clamp that down too...
FINALLY could build/hold the 5 to 7 pounds of pressure I try to run...
My transfer case blows bubbles from around the shifter arms and seals.
Again, same thing.
The pressure isn't high enough to dislodge the seals, yet everywhere you see bubbles, there WOULD HAVE BEEN WATER GETTING IN!
Even my distributor blows bubbles while it's running quite happily SUBMERGED in water....
Positive pressure, even small amounts of positive pressure, will keep water from entering.
I pressurize the distributor cap, differential housings, transmission and transfer case with air pressure.
They blow bubbles instead of filling with water.
Once the compressor is on and the regulator is turned over to the drive train/ignition, I have no issues what so ever driving into water up to my dash...
We often back down into the lake to clean up the vehicle after being in the huge mud pits we have around here.
That mud STINKS, it's corrosive, and it's better washed off the vehicle,
So with my ELECTRIC compressor running (and engine often turned off while we wash things out) we back down into the lake with the water often up to, and sometimes over the hood, and splash around a while.
It's a REAL refresher when it's 105 degrees outside,
And we have NO ISSUES with getting the vehicle started again, or getting water in the axles/transmission/transfer case.
Why do you think I have a thread to the ignition and waterproofing hubs/axles and stuff on my signature?
We like it WET around here!
Compressor inlet is in the windshield frame, WAY up high over the water level, and as long as my WATERTIGHT ELECTRIC COMPRESSOR runs, no water gets into the components where it will do damage...
FLAT FREAKS PEOPLE OUT when they see us out there with water up to the hood and us out splashing around!
Now, before you try this, be advised, I spent quite a bit of time getting the engine water tight!
Snorkel, vents for crankcase, ect...
And you WILL occasionally get water in the fuel tank if you aren't careful and your emissions system is still in place!
That charcoal canister WILL suck in water if you don't see to the issue!
With a SECONDARY distribution block and a regulator, it's not an issue to pressurize everything.
It's simply two valves.
One is the 'Atmosphere' vent that the components normally run on, and you CLOSE that one.
Then you open the pressure valve so the block pressurizes the components from the pressure regulator.
Nothing to it.
When you are done in the lake, mud pits, ect.
You simply turn the air valve 'Off' and turn the vent back 'On'...
Takes longer to dial down the regulator than to waterproof the drive train.