A friend who has passed away once told me about a compressor set up that eliminates the pressure loss and “recharge” cycle for HVLP spraying. I remember that it involved using two compressors in series so that one was continuously running to “top off” the other, which in turn supplied the tool with consistent air.
It made sense at the time, but now that I actually want to do it I’m having trouble wrapping my mind around the specifics.
I’ve got a good sized two-tank compressor (contractor style) and a couple of smaller ones meant for trim nailing, etc. (these are single-tank, very portable but low capacity and relatively slow filling.
Can anyone walk me through the basics of this set up?
Replies
I think you're confusing hvlp with standard compressed air for spraying. In hvlp, very little air, in cfm, is needed. High volume at low pressure. Prior to this, air was used at much greater rates, in a setup you describe, like 60-100 psi to power the gun. Your friend is describing a simple way to boost the amount of air stored for standard spraying, before the compressor starts cycling, if I read you right.
Jackplane, That makes sense - my friend was likely talking about a higher demand system. My HVLP rigs usually keep performing throughout the cycle without much trouble. Still, I'm interested in a set up by which I could avoid the pressure drop and down time that I experience with more demanding air tools, like nailers and such. I've always resisted buying an air sander, for instance, because I would expect there to be more waiting than working. But I know that many auto body shops use them all day, so they must be very effective, high rpm, etc.. I don't have the space/inclination to own a huge tank compressor, and simply boosting storage capacity would also slow recharge time. I was picturing running a primary compressor in line and adjusting the on/ off ranges in such a way as to create a "running toilet" effect to keep the secondary tank topped off so it never cycles down. I was just wondering how exactly this might be done, and in what order I would use my respectively sized machines. Thanks!
This really depends upon the HVLP gun you're using. Some of them require 14 cfm or more even at low pressure. Others require only 4-9 cfm - it really depends upon the manufacturer. If you look at SATA, most of their guns are low CFM. Compare that with DeVilbiss or Binks and you'll see a great difference in air requirements. There are also dedicated units like Fuji which have 3 and 4 stage turbine fans to provide the required aif flow.
The answer to you question is to do a little research on HVLP guns first. Then look at dedicated fan systems like the Fuji or Campbell Hausfeld HVLP systems. You can find an HVLP gun that will work with a single compressor, but if you get one that requires 14 or more CFM, you'll either have to use the double compressor system like you mentioned or get a dedicated turbine/fan unit.
If you hook up two compressors in series you essentially have a two stage compressor - good for higher pressures. Two stage compressors commonly yield pressures of 175 psi. It would seem to me that you want more volume of air, not more pressure. To do that you would put them in parallel, not series.
Tinkerer, that's right -I've never needed more pressure, when the tanks are topped off. The problem arises when a particular tool has depleted the tank pressure to where it's lingering just above the bottom of the cycle. When I reach for the tool for another flurry of operation (nailing, sanding, whatever), The motor kicks on but the tool demand exceeds the ability of the compressor to keep up.
I happen to have two very small rigs (for trim nailing) and one larger, two tank compressor. Just for fun let's say I wanted to use them all at once to feed one very demanding (volume wise) tool. If I understand your terminology, a parallel arrangement would mean that all three machines would "T", or actually "+" together somewhere en route to the demand.
This is where I get confused. First, could it be that simple? Could the three tools work side by side just cycling at different times? If you had their lines converge into only one regulator to control output, wouldn't they equalize amongst themselves? I guess then you'd have the equivalent of one large (if wierdly shaped) tank with three potential suppliers (compressors). But only one of these, the one with the highest "low" trigger, would be doing all the work.
If the lines were to converge AFTER their respective reg's, would you need a fourth regulator set at the lowest psi to supply the tool? I guess I'm hung up on the regulators issue - how to set them, etc.
If I were to set them up in a sigle file line, each supplying the next towards the tool, would this be a "three stage " compressor? My initial thought was that they would be arranged with increasing demand so that the one next to the tool would always have what it needed. It seems like this is what basically goes on with a single tank and compressor, if the tool/hose itself is looked at as a "tank" where the initial demand is created.
Even if I never end up trying any of this, it's an interesting subject. I'd like to hear your thoughts.
"Tanks" alot ; )
Let me explain series more thoroughly so you will know that you don't need that. In a series the first pump or more likely cylinder in a compressor pumps directly into the second cylinder. The first cylinder is much larger diameter because it takes air at room pressure and compresses it into a small volume at approximately 90 psi. A lot of heat developed as the air is pressurized so the pipe that delivers that air is finned to dissipate the heat. (This heat is produced with the same principal as that heats or cools your house with a heat pump.) The second cylinder(or piston) takes that smaller volume of air and compresses it even more making a much smaller volume and yet higher pressure, usually up to 175 psi. This is very useful in a tire shop as a truck tire that should have a pressure of say 85 psi would take much longer to pump up with a 90 than a 175 psi supply. You can see that the higher pressure is a waste of energy and machinery if your pressure needs are only half that much. Sorry if this is overly elemental, please skip.
Single stage or more than one pump supplying air pressure in parallel. Whether you have one or more pumps supplying air into a single pipe, a tank in between, or each pump having its own tank and hooked together some way doesn't make to much difference - It is all one air supply. Since it is one air supply it has one pressure unless there is a restrictive passage for the air somewhere in the system. If the different pumps are set to turn on different pressures, the one set to the highest pressure will turn on at it's set pressure. If that pump does not sustain the pressure and as the pressure continues down the pump set to turn on at the next lower pressure will kick in and so forth. Hopefully the pump set to kick in at at lowest pressure will sustain the desired volume of air.
The same thing will happen at the higher pressure end. As the pressure rises in the tank/s the pump set to cut off at the lowest pressure will do so at that pressure and the pump set to cut off at the highest pressure will cut off when that pressure is reached. The settings of the two pressure switches could be almost identical or could be vastly different. or the two or more pumps could could be hooked in parallel to the same pressure switch in which case they would turn on and off at the same time.
I think you might me confusing the pressure switch that operates the pump with the inline regulator. I've tried to explain the pressure switch. The regulator merely reduces the pressure that the tool receives by a preselect adjustment. The regulator is not hooked up to the electric supply and does not affect the pumps in any way except as they regulate the air drain from the pressure tank/s the pressure switch/s kick the pump in at a preselect pressure.
Lastly, the term "Tanks a lot" is reserved for only native Scandinavians. There being no "Th" sound in the Swedish language the immigrant would use the "T" sound instead. When I was a kid, I would trick my grandma into saying a word like "Thank you." Then when she said "tankyou" I would laugh, which she didn't take kindly to. Hey, I'm open for further discussion.
Great explaination especially since I am from swedish heritage. My only question is do the regulators have check valves in them. For example two compressors have the pressure switches set to come on at 90 psi and cutoff at 150 psi but both compressors are regulated to deliver 60 psi.
Duh! I guess I just answered my own question. Even if they don't have check valves one compressor will not have a negative impact on the other because it does not reach the pressure set points to engage the other compressor. Please excuse the ramblings of my swedish brain.
Tinkerer, Thank you for the lesson - I've always wondered about this stuff. I may have referred to the p.s. as a "regulator" itself because it has a needle guage and is often adjustable, but I do understand the difference between that and the line regulator - sorry if I was unclear.
My real confusion was about check valves, like CT was wondering. I think we both seem to get it now. Two compressors working in parallel as you've described would each work as much as their respective settings compelled them to, if the demand was there. It's like an adult and a child on a tandem bike; each can stop and stop pedalling when they need to, but both will contribute to the effort. Right?
BTW If I'd known you were Scandanavian, I'd have posted this as a Finish question.
Now you can teach me. By the way, do you know why they paint fire engines red?
Well you know that fire engines carry water. Water is found in the sea. In the sea, there are fish. Fish have Fins. In the second World War the Fins faught the Russians. At that time, the Russians were communists. Communists, you know, are known as RED. So now you know why they paint fire engines red.
Edited 1/30/2006 9:53 pm ET by tinkerer2
That's fascinating. I do know that, in the U.N. , the distance from your office to the bathroom determines whether you're Russian or European.
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