Anyone run dissimilar compressors in tandem?

[Stytooner]

Reserves might mean a lot when using two systems. If you hook them together, a better way may be to unplug the least productive or most cycling and use the tanks from both. Depending on the piping, that may produce better CFM.

I know for some of the Furniture Factories I did Maint. at, we used screw type air compressors. Replaced banks of smaller piston type. Always had plenty air.

[LCHIEN]

...

One way would be to time how long it takes to charge a known volume to a given pressure. Recall that CFM is measured at a particular pressure, so given a 10 cu ft volume for example and a 6.3 cfm @90 psi, it should take [10 cu ft/6.3 cfm] =1.58 minutes or about 95 seconds to charge that volume. This is sort of a gross approximation, but it may get you in the ballpark anyway.

...

there's several problems with this technique. Some basic rules of pressure and flow:
1. Air is highly compressible.
2. CFM is really standard cubic feet per minute (SCFM) which refers to the volume of air as if it were at atmospheric presure. So a tank that 10.3 cu ft is really 61.8 standard cu feet if the air inside is at 90 PSI (6 atmospheres).
3. the flow rate of a compressor is dramatically affected by the pressure into which it is pumping. Usually they specify it at 40 PSI and 90 PSI. e.g. Daves 29 gallon compressor spec:
CFM @ 90PSI = 5.9
CFM @ 40PSI = 7.3

so a CFM measurement must always be given with an @ xxx PSI rating and if your tank starts at 0 and goes to 90 what are you going to put as the pressure? The pressure has to be constant for the CFMs to have any real meaning.

The good news is that if its at 90 PSI then the volume of air in that tanks is really 61 Cu FT. But much of it was pimped near zero PSI where the compressor rate is the very highest because it takes much less work to pump against z or a few PSI. So such a number would be meaningless for evaluatio of what tool it could run.

[dbhost]

Well, again like I said, experiment. If it fails, ti fails... And I go back to using only the 29 gallon... I haven't had the impact on any fasteners since that crap blew out of the exhaust port, and it IS flowing a LOT freer now... I am thinking that plastic MUST have been something that got in the inlet at the factory somehow, and they just kept screwing it together instead of removing the plastic before... If that is the case, my low power on the impact problem may be solved anyway...

I have no clue how Husky managed to rate the siphon feed gun at 9CFM, but I ran that a LOT on the old 8 gallon compressor with no problems... I guess if you open everything up all the way, pull the trigger and hold it without feathering then yeah, you could suck up 9CFM... Then again a blow gun held open will use 10 or more...

I should mention, the reason I kept the 8 gallon was for portable function. Such as the impending shed build. I would rather roll a small compressor to the back yard that drag a hose all the way from the shop either around the house, or through the house to get to the back yard...

[woodturner]

there's several problems with this technique.

Good points, and upon reflection the "gross" measurement would be a lot less accurate than I originally speculated.

I found this article on the web that suggests the error in "my" method may be in the range of 30%:
http://truetex.com/aircompressors.htm

So much for that idea.

I keep pondering whether there might be a way to use a water tube manometer to somehow "back into" a volume measurement. It's an easy instrument to make, but measures pressure rather than volume. Haven't figured anything out yet, though.

[LCHIEN]

Good points, and upon reflection the "gross" measurement would be a lot less accurate than I originally speculated.

I found this article on the web that suggests the error in "my" method may be in the range of 30%:
http://truetex.com/aircompressors.htm

So much for that idea.

I keep pondering whether there might be a way to use a water tube manometer to somehow "back into" a volume measurement. It's an easy instrument to make, but measures pressure rather than volume. Haven't figured anything out yet, though.

the method in the article was going from 85 PSI to 102 PSI. Your method was gong from 0 to 90 PSI. Your error would have been a great deal larger than 30%.

[LCHIEN]

the other thing we forgot to discuss is duty cycle. If your compressor is capable of putting out say 10 CFM continuously, you don't want to draw 10 CFM from it...
you need to draw a fraction of that, say 5 CFM so your compressor can run and stopp with about a 50% duty cycle, the length of time of each run being governed by the size of the tank. A larger tank will have a longer run to time to refill it but will be able to rest longer as it is drawn down again.

Running your compressor 100% flat out is probably bad for it. and the compressor pump may overheat. If you run too close to 100% on the high end, like 101%, then the air in your tank will be on a continuous decrease and ultimately your regulator will fail to regulate and your tools will be working underpressured.

Just a thought.

[dbhost]

Okay maybe I am trying to fix a problem attacking it from an air supply perspective when it may be a tool problem...

What is known...
#1. All of my air tools work with the 29 gallon compressor.
#2. All of them with the exception of the Earthquake impact gun work exceptionally well on the 29 gallon compressor.
#3. The HVLP, and even the Husky siphon feed spray gun both work VERY well with this compressor. Of course that is assuming I am spraying, and stopping as I change directions in my sweep as you are supposed to...
#4. If I am going full bore, with most tools, there is about 5 minutes or more before the compressor kicks on to refill the tank, and it runs in short bursts, maybe 30 seconds... Except for the die grinder. It cycles the compressor sooner, but I don't run it hard like that often. Usually it gets used for 30 seconds or less...
#5. The impact wrench is delivering low power. That is my issue.
#6. Since I did the oil soak and blew the junk out of the impact, I have not had it on a bolt. For all I know, that plastic junk that spit out of the exhaust port was what was holding my impact back.
#7. If indeed the impact is okay, and will run fine on the 29 gallon, I am disconnecting the 8 gallon soonest possible, and cleaning up my plumbing. I may end up connecting from regulator / filter to the reel using copper pipe. The distance is short, and I would have to modify an air hose anyway, might as well bump up the volume capacity in that line / remove restriction. Not to mention insure better longevity of that part of the system.
#8. If the impact is okay but the 29 gallon compressor is just a shave too small, a 60 gallon compressor is too tall for my installation, thus my next option is keep the 8 gallon in the system for those times I need to run it, OR get rid of it and get the Husky that only draws 4 SCFM.

[mpc]

Paint sprayers, sand blasters, grinders... those are the long-term high-CFM tools typically. Impact guns take high CFM for short bursts only. If your compressor can run the paint gun and die grinder adequately it's plenty big enough for the vast majority of impact guns; only guns designed for tractor-trailers, bridge building, etc. would need more CFM. When running from the tank, a compressor's CFMs are limited by the hose size and flow capacity of the regulator - the tank alone can deliver a LOT of CFMs for a few seconds at least if not a minute or two. If you continue to have problems with the impact gun I'd say the gun itself has internal problems.

Many compressors come with regulators that do limit the CFM flow rate too much; my 20 gallon 2HP Craftsman unit (100psi max, rated for 6CFM at 90psi) struggled with some air tools until I replaced the regulator. Those tools should have worked on a 6CFM @90psi compressor... but didn't. Yet my compressor wasn't running even 50% duty cycle... ergo the tool performance wasn't being limited by the motor+pump, tool performance was being limited by the skinny air passages inside the regulator. I ended up installing a "T" between the tank and regulator with a separate shutoff valve on the new leg; with this leg I ran "unregulated" pressure to my air-gulping tools. Since my compressor cycles between 80psi min and 100psi max I wasn't worried about it; folks with 125psi or even 150psi compressors can't do this as most tools aren't rated for such high pressures. A regulator with half inch fittings, instead of the typical factory/stock quarter inch or 3/8ths fittings, will flow a lot more CFMs and was the final fix for my compressor.

mpc

[JimD]

The tank should have given you enough air for most fasteners. You were getting the fully 90 psi (or whatever you are regulated at) until the compressor kicked in, then perhaps a bit less. So the thought that the CFM is not your issue is correct IMHO.

If you want to tie the compressors together, even sometimes, I would think about running a hard line around the shop to the two compressors and the hose reel. That would greatly reduce the losses in the plumbing. For your compressors, I would also change the regulator settings. I would have the bigger unit kick in at a higher pressure than the lower. Since it's rated 150psi, you could set it over 100 psi (maybe even 125 psi) and then set the little one at 100psi. That way the little one only kicks in if the big one really cannot handle the demand. If you don't use different regulator settings to determine which one comes on first, the difference in the regulators will probably determine it for you. In other words, if both are set at 100psi but one regulator really kicks in at 105psi, that compressor will run unless the pressure drops below the other regulator and then both will run.

I don't see why the compressors wouldn't be additive if you don't waste the additional capacity in the line losses. I would think being able to add the little one, sometimes, would be useful. But not for making the impact gun work. It should work regardless (if in good working order).

[dbhost]

JimD, that is about the best explanation I have seen of the deal yet...

When I use pnuematic tools, for the most part, they don't cycle the compressor all that much, and with the exception of spraying, I don't keep going too long after the compressor kicks on. For example an air ratchet. The compressor typically comes on about 90% of the way when removing say 4 or 5 large bolts / nuts, and 4 or 5 extra revolutions isn't going to hurt anything...

Spraying / not stopping has never been a problem. The compressor does keep up.

Again, the only real issue I have ever had air supply wise has been the impact gun is just underpowered, badly... And like I said, it really hasn't bee put on a bolt since I did the oil soak / blowout thing. I suspect the problem may be gone.

IF the problem is indeed gone my plan moving forward is...

#1. Remove the Tee from the line to the regulator, just connect the 3' whip directly to the regulator input, and the other end keep the male quick connect to the compressor.
#2. Mount up the reel.
#3. Assuming I can figure out how to do it without burning down the house, since the hose reel will be so close to the compressor. I would likely keep the 8' hose as it was remnant, cheaper than the 3' hose, and would make a good donor along with an end repair kit to make a 1' whip to go from the copper to the reel.

I would have a shopping list, and a skill to pick up if I did this though. The skill would be soldering copper pipe. I have never done that before but I do understand the process. I CAN fab this all up on my machinists vise / on the bench and then mount it to the wall / ceiling with no problems though, so I am not too concerned.

The shopping list would look like this...

1. Assuming it could be cut with my tubing cutters, 2 sections of 10' 1/2" Type M Copper pipe.
2. 2 1/2" 90 degree copper elbows. 1 to go from the vertical to the horizontal to get from wall to ceiling, the other to go from horizontal to get from ceiling to reel.
3. 1/2" copper tee. This is set to the side points to the outlet of the regulator, and the down side goes to a short piece of pipe and a ball valve for draining the line.
4. Copper 1/2" C x 3/8 M MPT pipe thread adapter to connect between the Tee and the filter / regulator.
5. 2 @ copper 1/2 C x 1/4 Male MPT to connect quick connector for connecting copper to whip for reel.
6. Copper 1/2 x 1/2 NPT Male to connect to a 1/2" ball valve to dump the line.
7. 1/2" FPT ball valve to dump the line.
8. I can't find the link for this stuff, but copper pipe flux and solder.
9. 2 @ 5 pack 1/2" copper pipe clamps
10. Air Hose repair kit to take that 8 footer and shorten it up to make that connector whip.

Of course I will need to dig out the torch, and a can of propane for this as well. Since my glue brushes are nothing more than solder flux brushes, I have those covered. I have the plumbers teflon tape as well.

This is something I have never done before, so it will be a learning experience. I have brazed a few brass radiators, and done plenty of electrical soldering. I assume the process for copper solder is somewhat similar to electrical. Apply flux to the mating faces, connect them, heat them, apply solder throughout the joint allowing the flux to make the solder flow INTO the joint. Am I correct in my understanding of this? I wouldn't think brazing with Oxy - Acetylene would be the right approach for something this thin walled, but I have read somewhere that is exactly what some folks are doing with compressed air copper systems... Would a soldered joint not be strong enough to hold the 125/150 ish PSI my compressor is capable of?

[capncarl]

When you get through with you system you will have a pretty system! For a lot less you can pipe it in with threaded galvanized or black iron piping. A lot of hardware stores will cut and thread the pipe for you if you buy it there, and it will be a lot more durable.

[dbhost]

Hadn't considered black iron. That would cut the cost of those pipe to thread adapters out, just need bell reducers instead.

Worth serious consideration...

[JimD]

You may want to check out this outfit:

http://www.rapidairproducts.com/stor...2&cat=Rapidair

It would be a lot easier to run one of their nylon (or aluminum) systems than to use copper or iron pipe. Cost may not be that different, I haven't priced it out. It just slips together.

Soldering copper is indeed easy. I haven't done it for air supply but have soldered piping together for home plumbing many times. It is mostly getting the pipe and fittings clean. Sand paper works fine for the outside of the tubing but you need a wire brush for the inside of the fittings. Home centers have them. After the joint is clean (best to clean up all the joints in an area and solder them at onece) you flux it, put it together, and then put the heat on the piece with the biggest cross section. When the temperature is right, it will draw the solder into the joint. You will want a wet rag on hand to wipe the joint cooling it enough it sets up and getting rid of excess solder. I like Mapp gas because it's hotter and speeds up the process. Propane works, however.

Jim

[capncarl]

I haven't compared cost of these compressed air "hose" systems with the push-lock type connectors. They look good and should be easy to install. I did price compare a underground sprinkler system pvc vrs comparable size blue plastic hose with large push-lock fittings. 3x material cost. Your labor is free so I expect the same on these small air systems. Kinda like buying a piece of 4" flex dust collector hose. It is just cheap hose priced at about $2.5 per lf.

[woodturner]

I would have a shopping list, and a skill to pick up if I did this though. The skill would be soldering copper pipe.

Copper pipe can be used, but the requirements may be different than for water systems.

As others have suggested, black iron or galvanized pipe that is already rated for compressed gas use may be a better option.

Here is a web page that compares piping options
http://www.exair.com/en-US/Primary%2...AirPiping.aspx