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Thursday, Sep 2, 2010
| Off-Road.Com Tech Sectoion On-Board Air SystemI'll start with a brief explanation of how my Air-Bar functions as an on-board air system. Basically I have a full-cage that will hold approximately 3.5 gallons of air that is automatically filled by an automotive air-conditioning compressor when the pressure inside the roll-gage drops below 100psi. When the air pressure reached 145psi the compressor is turned off and the air line from the compressor to the roll-cage is drained. Pretty simple! There are two types of automotive air-compressors that are in use today. One type is cylindrical in appearance with the pulley on one end of the cylinder and the air inlet and outlet on the other end. The other type is some what square in shape and can be identified by its cast aluminum housing. This type is said to have and internal oil reservoir separate from the air channels. This type is superior because the air that is pumped out is oil-free. I must add that I have seen some of these compressors that do spray out oil like the cylinder type. I picked out my compressor from a pile at a junk yard for a mere $12.50! Ideally, it would be best to remove one, with brackets and pulleys from a wrecked auto with the similar engine. This way you would know where the factory mounted it and save the hassle of making your own brackets. Fabricating your own brackets, like I did, can be time consuming, but you can choose where to mount it. When buying an used compressor, you must make sure that it has not "frozen-up" and still pumps air. This can be done very easily by turning the pulley and covering the outlet with your hand. Pressure should build up as the pulley is turned and be noticeable when your hand is removed. One other important note is the condition of the magnetic clutch which engages the compressor. The pulley should be able to turn freely without friction between it and the clutch. If the magnetic clutch is not working properly you are better off buying a different compressor. Another alternative is to go down to your local auto parts store a purchasing a rebuilt compressor, brackets, pulleys (you will need two, one for the compressor and one for the fan) and v-belt ($$$). Once the compressor has been bolted to the engine block in a safe and secure manner, you must find a v-belt to turn it. This is when you will be glad that you took off not only the compressor and brackets from the donor vehicle, but the fan pulley and belt as well. This saves you the trouble of trying to measure the distance and buy one to fit. Now it is time to test the compressor to see if it sprays out oil as well as air. Your compressor should have two terminals, positive and negative. The negative should be well grounded. The magnetic clutch will engage when the other terminal has a hot wire to it. Place your hand near the outlet to determine whether or not oil is being pumped out. If so, you will need to purchase an in-line air filter. Replace the drain valve on the filter with one that you can connect a piece of small plastic tubing. This tubing should be routed to the inlet. This will allow you to drain any accumulated oil back into the pump to ensure that it is well lubricated. The inlet should have some type of filter attached to it so that it is breathing clean. I bought a $1.95 small engine air filter and cut a hole in the top to run the drain tubing through and it works just fine. From the in-line air-filter you need to run high pressure air hose to the tank. Before you attach to the tank you must have a one-way valve and then a brass tee to attache the pressureswitch. The one way valve will allow you connect a small piece of high pressure air tubing to the pressure switch. This tubing will drain the air from the compressor to the one-way valve. This relieves the seals inside the compressor of the 145psi which enables the compressor to start up again without a load, which can sometimes cause the belt to slip on the pulley if the tension is not properly set. The pressure switch will automatically drain the air when power to the compressor is shut off. Your air reservoir (tank) should have a drain valve (to drain any trapped oil or moisture), a pressure gauge, a quick-connect coupler, and a 150psi pop-off valve (this valve will open at 150psi to ensure that the tank will not explode under pressure should your pressure switch fail, air compressors can pump up to 300-400psi!). I choose a 150 psi pop-off valve because the glass in-line air filter is rated a 150 psi maximum. If you do not need this filter keep in mind the maximum reading on your pressure gauge as well as the other components in the system. The inlet and outlet of you air reservoir should be far enough apart to keep unwanted oil and moisture from exiting the quick-connect coupler. Now for the wiring of the pressure switch and the compressor. I found an extra accessory post on my fuse block and ran a wire from that to a switch and then to the pressure switch. The pressure switch (approximately $20) has another terminal where you will run a wire to the hot terminal on the compressor. A wire that is only hot when the key is turned on rather than an always hot wire is preferred. If the pressure in your tank drops and the pressure switch activates the magnetic clutch, the resulting draw can leave you with a dead battery in the morning. I have installed a "master control switch" to turn the power off in the case of a malfunction, a blown hose would keep your compressor running constantly. The psi at which the pressure switch is activated can be adjusted to your needs with a simple Phillips screwdriver. One additional feature that is worth adding is a hand throttle or better yet, a electric solenoid to advance the idle speed when the compressor is activated by the pressure switch. This would ensure that your reservoir would be filled up rapidly as you are filling up your tires. Darin Smith. |
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