On-Board Air Compressor
Article by Ed Holnagel
First of all, let me say that we have done a lot of work engineering our On-Board air compressors and I have to say that to believe that you can install from scratch an on-board air system for as little as $150.00 as some have claimed is in error.
Trust me! You cannot install an on-board air system for this kind of money and do it right. I will explain, read on.
Common Misconceptions:
-
"York compressors won't put oil out in the air." ALL of the air conditioning compressors will put oil out with the air, the York just puts out less. You have to be sure to mount the York the correct way for this to be true. The reason the York passes less oil is that it has an internal oil return gallery to the oil sump on the output side of the compressor.
-
"I can just use a simple filter from Home Depot to get the oil out." Wrong! You must use an oil removal or "coalescing" filter to remove oil from the air supply. No the cheap filters at Home Depot are NOT coalescing. If they don't say "Oil Removal" or "Coalescing" on them then they don't remove oil. A good coalescing filter will start at around $60 and they go up from there.
-
"I can just coat the inside of a Sanden compressor with Prolong or Slick 50 and I won't have to put any more oil in for a couple of months." Again, trust me, we have done this and it DOESN'T WORK!!!!
-
"I can use an air tool oiler to keep my compressor lubricated." Thanks for playing our little game but YOUR OUT! An air tool oiler does not have the capacity to provide enough oil to your compressor to keep it working, again, trust me, we've tried it! You must use a mist lubricator. These are about the same size and shape as the coalescing filter but they have an adjustable drip rate that you can see through a bubble in the top of them that provides oil directly into the intake on the compressor. These lubricators usually start at around $28.00.
-
"I just use 10W-40 to lubricate my compressor" I hear that some people do this and maybe it works but regular motor oil will over time build up a varnish inside your compressor that isn't good. Use air compressor oil available from a compressor supply store, Home Depot or the auto parts store. This oil is more like a mineral oil and will be clear and almost water like in viscosity.
Components in a compressed air system
In order to correctly set up your compressed air system you will need some basic and essential items to insure continued operation of the compressor and oil/water free air for your tools, air lockers and tires. Below is a list of the required components in the order they should be installed following the compressor.
Mist Lubricator. The mist lubricator is installed on the intake of the air compressor. Looking almost identical to the Coalescing filter pictured below the Mist Lubricator is vital to keeping your air compressor running. The bubble on the top of the lubricator allows you to see the drips of oil as they enter the air stream. There is an adjuster on the top that allows you to vary the amount of oil that is fed into the air entering the compressor. Be sure to fill the bowl of the lubricator with compressor oil, available from many local hardware shops as well as Home Depot.
Coalescing (oil removal) filter. This is a filter that is specifically designed to remove oil from the air. It should be the first thing down stream from the compressor to ensure that the rest of the air system stays oil free. Better coalescing filters will have a gauge bubble on top that will indicate when the filter is saturated and in need of replacement. I cannot stress enough how important this filter is to your air system, not to mention your lockers, tires etc.! You can find these filters with either manual or automatic drain valves. With the automatic drain the filter will drain off the trapped oil when the catch bowl fills to about half full. Manual drain filters have a petcock at the bottom that must be opened periodically to drain off trapped oil. I have seen where some will run a return line from the bottom of the filter back to the intake of the compressor. I would advise against this because the coalescing filter will also remove moisture from the compressed air. I do not want to be putting watered down oil back into my compressor and I don't think you do either.
Check/Unloader valve. The Check/Unloader valve should be located after the coalescing filter and close to the pressure switch. This valve only allows air to flow in one direction. The unloader part of the valve has an open port on the compressor side of the valve that is connected by a copper tube to a valve on the pressure switch.
When the pressure switch turns off the compressor it also opens a valve that bleeds the pressure (via the Check/Unloader valve) from the compressor side of the system. This ensures that the compressor is not started under pressure on the next cycle. If you have an electric compressor at home you will notice this when the compressor shuts off and is followed by a hissing sound as the pressure is bled from the pump side of the system. This is a very important process for electrically driven compressors because it insures that the motor isn't starting under a load on the next cycle. However for engine driven compressors it is less of a concern. Consider the use of the Check/Unloader valve to be optional. It does provide the advantage of being able to remove the compressor from the system without loosing pressure downstream though.
Pressure Switch with unloader port. The pressure switch senses the pressure of the system and shuts off or turns on the compressor at the preset pressures. Usually it turns on at around 85psi and turns off at 120psi. The unloader port is for the above mentioned connection to the Check/Unloader valve. If you are going to omit the Check/Unloader valve from your system then you can buy a pressure switch without the unloader port and save some money.
Pressure safety (pop off) valve. These valves come in varying pressure calibrations and open at the preset pressure to keep the system safe in the event that the pressure switch does not shut off the compressor. If you have a 125psi system it is common to use a valve no higher than 150psi. Most components in a standard system are safe to about 175-250psi, so a 150 psi valve will work just fine. The safety valve can be located anywhere in the system after the check/unloader valve. One of the extra ports on the stem of the pressure switch is a good location. It helps to have it in a location where it can't ingest dirt or mud and allow access to the pull ring on the end if you need to manually bleed off the pressure in your system.
Tank. For storing air, the tank is important in that it helps to keep the duty cycle of the compressor pump down. For most short wheelbase Jeeps about the best you can hope for is about a 2.5gal tank. Some people do use their rock slider bars or bumpers to store air, but be warned that the tank does collect condensed moisture from the air and therefore must have a way to be drained or your slider bars will rust from the inside out!
Standard water/particulate filter. These are the filters you will usually find at your local hardware or Home Depot store. They are for removing water and particulate matter from the air before it gets to anything crucial (like your air lockers!). Be sure to use a filter with a metal catch bowl as the polycarbonate bowls will deteriorate in the under hood temperatures that the engine produces. As I have stated before, clean air is of the utmost importance. Do not skimp on filters. Air leaving your air tank at a high pressure will condense and carry a large amount of water with it.
NOTE: Look for filters with at least a 175 degree rating and try to locate all components as far from the engine and especially the exhaust manifold as possible.
Pressure regulator. The pressure regulator should be installed and set to around 90psi. This is the pressure that almost all air tools run at and is near the lower limit needed by ARB Air Lockers to operate. If you need to save space you can buy a combination filter/regulator in one unit that incorporates the above filter with a regulator.
Air disconnects. This is where you will connect your air hose to the system for airing up your tires or running air tools. You can actually have multiple disconnects (or "drops" as they are called) but realistically you should only have them after the pressure regulator. This will ensure that you are getting the cleanest air and that the air is regulated to keep the duty cycle down on the compressor.