Question
I am setting up a new air compressor in my one man shop. It is a 5hp Quincy, rated at 16 cfm at 90 psi. My main use for the machine is to run an Accuspray HVLP conversion gun. I will also use it for my pin and brad guns.
How are you filtering air on your compressors? I am starting with a basic 5 micron filter/regulator that is supposed to remove particles and water. I planned on mounting this right at the outlet on the tank. Obviously I want to have the air clean and dry enough for spraying, but I am not sure of how much filtration I need. Are there any smaller type desiccant dryers that I should be using? Also, should there be a coalescing filter in the loop to catch any potential oil from the pump, or this is overkill?
I don’t spray daily, more like every couple of weeks, if the usage makes a difference as far as how far to go with the filtration.
Forum Responses
(Cabinetmaking Forum)
From contributor L:
Yes, use the oil filter too. You have the placement of the water filter wrong, though. You need to place it farther from the compressor. It works best when the air is cooler, not straight out of the tank. Place the oil filter after the water filter. I don't use a desiccant dryer and I don't have problems finishing. I'm in the NE USA, not the most humid place, but at times it gets there.
Run metal plumbing which will help cool the warm compressed air to help the water vapor condense into liquid water. Copper is a good way to go because it will not rust and introduce pipe scale into your system.
If possible, run the main plumbing lines on the outside of the building to further help cool the compressed air.
Run the plumbing at about 1/4" per foot gradient and have it angled to drain back towards the compressor and away from your filter stations.
Install drip legs complete with drain cocks nearby and upstream from your filter location/locations. Install a drip leg just downstream from the compressor itself to keep as much of the system’s liquid water as possible from getting into and rusting your compressor’s air tank.
As contributor L said, install a coalescing oil filter\filters downstream from the water trap\traps.
There are a lot of desiccant dryers on the market. You would want to have these located as close as possible to the actual point of use in the spray finishing operation to avoid having the air cool further after being dried and resulting in more water condensing and mixing with the paint. They make some fairly inexpensive "point of use" desiccant driers. These have a very small capacity and would become saturated quickly if the air is very wet or the use time very lengthy. They are usually sold as for a one time use, but you can easily replace the desiccant yourself and reuse them. Saturated desiccant can also be dried in an oven or other source of heat and then reused.
As I see it, it would take a lot of liquid water to plug the 3/4" ID of the copper pipe with ice to the point where you had less than 1/4" ID of flow, which is usually sufficient. With my system and climate, I doubt I ever get more than 1/32" ice blockage on the bottom of the pipe. And as pointed out, the air is usually fairly dry, anyway, at those extremely cold temperatures.
I think if you are going to do a new compressed air plumbing installation and it is possible to run the main lines outside of the building, it is worth it, because drier air is better for your equipment and especially for finishing. I doubt I would re-do an existing system that way unless I was in a climate that was causing major problems due to moisture in the compressed air.
Anyway, this type of system was recommended to me by a compressor supply company and it makes a lot of sense to me. Even from the standpoint of not having to negotiate interior obstacles while running the main lines was appealing to me for running my plumbing.
The main thing I wanted to point out to the original poster was, whether plumbing indoors or outdoors, try to have at least 40 feet of metal piping between the compressor and any water trap. Water in vapor form passes right through traps, so the air needs to have time to cool first.
My supplier told me that some shops with limited square footage will run their air through 50 feet of copper tubing that has been coiled inside of a 50 gallon drum so as to chill the air before it reaches any drying equipment.
I think I will run a copper loop on the ceiling of the first floor, and drop a leg on a wall for the water to drain to. Off of the wall leg, I will tee off to a filter set for my sprayer. This will hopefully be the point of driest air. I can come back up through the second floor for air use upstairs, which I originally planned to take right off the tank. This will also give me dry air compared to taking it off the tank.
Keep in mind that what you propose to do as far as the footage is concerned does not give you drier air. What it does is cool the air so that the content of water vapor becomes liquid water. So right before the first trap, you hopefully have cool but wet air. Then, after you go through a water trap and perhaps further downstream a desiccant drier, you have the drier air.
P.S. After you understand about how cooling the air turns the water vapor into liquid water which can be caught by traps, it also should make sense about the importance of having any desiccant driers as close as possible to the point of use in a finishing operation. You see, if you run 50 feet of compressed air plumbing and then go into a water trap… that’s fine. But if you then install a desiccant drier right downstream from the water trap and coalescing oil filter but have a 50 hose between the desiccant drier and the point of use in spray finishing… it is possible for the air to chill even further in that fifty feet of hose and bring more liquid water into your finish.
Desiccant driers also differ from standard water traps/filters in that they do remove water vapor. Apparently they don’t remove 100% or it wouldn't matter if you ran a lot of hose between the drier and the point of use.
Does anyone understand why the water vapor that can condense into liquid water after further cooling due to excess air line downstream from a desiccant drier will not affect a finish if there is no excess air line beyond the desiccant drier?
1. Particulate filtration: Weekly clean the inlet/suction filter of the compressor. Yours will have small foam or felt pads. Don't wash them, just knock/blow out the dust. Unless you have long runs of steel pipe after the compressor, you will not need any further particulate filtration for your machine tools. If there are long runs of old steel pipe, add filters as close to the points of use as possible.
2. Oil filtration: Bearing in mind that any oil carryover from the compressor will be in vapor form. Oil removal filtration should be positioned after your cooling/drying station.
3. Water removal: All compressors produce water vapor that downstream condenses as it cools, turning to liquid. However, even if this is drained off at an auto-drain filter, there will still be water vapor entrained in the air. This vapor condenses instantly at the point of air use as the pressure drops, e.g. at an air blowgun, inside your air tools (bad for 'em) and at paint spray guns where the water vapor mists with the paint, affecting what otherwise would be a superior paint finish.
Think twice before you decide to buy a desiccant dryer, as regenerative types will consume about 15% of the air produced by the compressor. All you should need for woodworking, including fine finish painting, is a refrigerated dryer. Make certain that the cfm rating is at least that of the compressor. Also make certain that it is located near to the compressor in the coolest but frost free and dust-free area, otherwise the performance will be affected. Keep it clean, especially the condenser.
A refrigerated dryer will typically condense and automatically drain off all water to a dewpoint of 4 degrees centigrade (39o f). Search Google to find out about pressure and atmospheric dewpoint.
A Thermal Mass Dryer (TMD) is a variation of the fridge dryer. Instead of the direct tube-in-tube type evaporator where the air is chilled by the refrigerant through the tube wall, the refrigerant in a TMD unit cools an integral tank of antifreeze (Glycol usually) which acts as a heat sink. The air then passes through a series of tubes or a tube coil within that chilled antifreeze, hence the heat from the air is adsorbed by the antifreeze.
The operating energy benefit of this type is significant where there are large horsepower motors involved with frequent and sometimes prolonged zero-flow of compressed air. The fridge unit simply stop/starts via a thermal sensor switch activated by the antifreeze temperature and sometimes by a parallel operating RH (relative humidity) switch in the downstream compressed air pipework.
There is, as usual, a price to pay in that TMDs are not so efficient despite what the manufacturer salesman may say. The chilled air temperature usually has a big swing margin, producing an average guaranteed dewpoint of only 10o C instead of 4o C. I doubt if you could obtain a TMD for such a small application as discussed here.
