The Hardware
This is where most of the money in an on-board air system usually ends up going, and it's also where the hardest-to-find parts are. There are a number of basic things (besides the compressor & tank) that you need:
- pressure switch
- safety valve
- pressure gauge
- 12V switch, fuse, wiring
- lots of fittings & plumbing
I'll go over each one of these in detail...
The Pressure Switch
A pressure switch is simply an automatic on/off switch for your
compressor that determines whether the compressor should be
on or off based on the air pressure in the system. If you use a
electric compressor, it controls the motor that runs the
compressor. In the case of a York compressor (or most other
automobile A/C compressors), it controls power to the
magnetic clutch. When the switch is on, the pulley (which is
always turning when the engine is running) turns the
compressor. When the switch is off, the pulley free-wheels.
I bought my pressure switch from an electrical supply store called Consolidated Parts in San Jose. It is preset to turn on at 95 psi, and turn off at 125 psi. It cost about $21.00.
The Safety Valve
Compressed air is one of those things that is relatively benign up to a
certain point, but can be dangerous when it gets too compressed. The
York compressor is quite capable of pumping air to 300-400 psi.
Many of the components used in a budget on-board air system can only withstand 150
or 200 psi. If your pressure switch fails for whatever reason, and doesn't switch off the
compressor, you want a backup fail-safe in place. That is the purpose of the safety
valve. It bleeds air out of the system when the pressure gets past a certain point. In my
case, the safety valve I got is rated at 145 psi, which is fine for me, since my plumbing
hose and pressure gauge are both rated for 200 psi. I got it at OSH for $12.99.
The Pressure Gauge
You could probably get away with not using a
pressure gauge, however, for the seven to ten bucks
it costs you, it's a worthwhile investment to have. I
picked up a 0-200 psi gauge with a 1/4" fitting for
$10 while I was in Canada over Christmas (which is
about $7.50 in US dollars). You can mount the gauge
under the hood, or plumb an air hose through and put it in your dash, next to the switch
& light mentioned below. Mine will be under the hood, and I may add another one in
the dash some time later.
The Wiring
In order for the compressor to work, you need to supply +12 volts to the wire that controls the magnetic clutch. This +12 should either come from a fused source in the fuse box (preferably one that is keyed to the ignition switch being on), or direct from the battery (with an inline fuse). The problem with running from the battery is that if you forget to shut the main switch off sometime, and you have any kind of leak in the air system, your magnetic clutch will be on while your Jeep is sitting in your driveway, and will eventually drain the battery.
You need a switch somewhere (I mounted mine right on the pressure switch housing) that provides power to the pressure switch. This is basically a manual override to keep the compressor from coming on when you don't need it. Since it takes about 15 seconds to fill my tank (1.8 gallons) to 100 psi from empty, keeping the system empty of air (at least while driving on the street) seems like a reasonable thing to do.
The Fittings & Plumbing
This is the most complicated part of the entire system, both from the complexity of the system itself, and the cost and difficulty of finding the parts and pieces for a reasonable price.
For plumbing, I bought a 25 foot long 3/8" rubber air hose at OSH (Orchard Supply Hardware) for $8.99. It has a standard 1/4" male fitting at each end, and is rated to 200 psi. This hose was cut to length to provide the connection between the manifold and the tank. I used the fitting end to attach to the manifold, and put a barbed connection on the tank. I've been told that the nylon brake hoses that big trucks use make a better tank supply hose, and they are easy to adapt from a compression fitting to 1/4" pipe fittings. They are more expensive than the hose I chose, but will last much longer.
I also bought a 25 foot long air hose coil, which is my main air supply hose from the system to whatever tool I am using (e.g., an air chuck or impact wrench or drill or die grinder or...). This was also from OSH, and cost $6.99.
The manifold is the piece (or pieces) that split the output from the
compressor to the various pieces mentions above (pressure
switch, safety valve, gauge, tank, and output). You basically need
an input (from the compressor's output) and five outputs, to go to
each of the above.
OSH and Home Depot both sell a cool-looking cast aluminum 1 -> 3 manifold. At OSH, the price was over $8.00, and at Home Depot, the price was $4.22. Guess where I bought mine... :-)
I bought two of them, for a total of eight holes. Two of the eight holes were used to join the two manifolds together. That left six holes, which coincidentally is exactly what I needed! You can get these manifolds in two sizes, 3/8" and 1/4". Since all of my plumbing (except the hoses) are 1/4", I got that size. Even on the 3/8" hose, the end connectors are 1/4".
So, in addition to the manifolds, I bought:
- two 3/8" barbed->1/4" threaded fittings (OSH, $0.99)
- two small hose clamps for above barbed fittings (OSH - $0.99 each)
- one brass 3" straight extender (since the pressure switch I bought is so big, you want to mount it above all the other stuff sticking out of the manifolds - OSH, $1.35)
- one brass 2" straight extender (to provide a male fitting for the quick-disconnect - OSH, $0.99)
- one brass 1" straight extender (to connect the two manifolds together - OSH, $0.99)
- two quick-disconnect plug & socket pairs (OSH - $2.72 each)
- one male/male joiner (a joiner that joins two male fittings -- OSH - $0.99)
- depending on what the hardware on your tank looks like, you may need a couple other fittings to connect the supply hose to the tank, and possibly plug one or more other fittings on the tank.
- one air chuck (OSH - $2.25)
- one roll Teflon tape to make air-tight connections (OSH, $0.99)
All in all, the hardware cost about $95.00, bringing the total to about $150.
Go back to my On-Board Air page.