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goleafsgo_12 02-27-2005 10:25 PM

Custom Air Compressor Guide
Ok guys, here is my brand new air compressor setup. I went to princess auto today, and bought 2 small compressors. The specs are: 2hp motor, 5.2cfm and 40psi, 4.2cfm and 90psi, one compressor has a 4 and the other a 5 gallon tank. They are the exact same compressor but I had got the other one a while ago, and this one was on sale now. So, with that said the 5 gallon was 144.44 (cdn dollars) and the 4 gallon 122.22 (cdn dollars).

I picked up a propane tank from a friend of mine. This tank was a 100lb tank, and was previously used for propane. This was used as an external tank to hold more volume of air. Then opened up the valve when nobody was around (becuase even an empty tank stinks something serious) and let all of the excess gas out of the tank. Then I removed the entire valve unit with a pipe wrench, tapping te wrench with a slede hammer when needed. DO NOT hit the valve with the hammer as you will probably do nothing but damage the tank. Anyways, I removed the valve so that only the threads that are cut into the tank were left. Since this tank was fairly large, it had 3/4" NPT (national pipe thread) threads. I left the tank with the valve off outside in the backyard for 3 days, at which point it still stank terrible. Filling it with soap and water, letting it sit and swish around, and dumping it does help.

Then I moved onto the compressors. Everything that I did was done to both compressors. I removed the regulator that control airflow to the tool so that maximum air could be sent to the external tank. I bought 2 air lines roughly 60" long with male ends on both. My compressor, like many, uses a 3/8" ID hose with 1/4" NPT fittings. So i bought a line for each compressor with those specs.

From the compressor, with the new lines, they run into a T fitting (1/4" NPT female ends). This connects both compressors together. From the T fitting it ran into a 1/4" NPT close nipple. From the nipple it ran into to a 1/2" NPT to 1/4" NPT reducer. From there I went from the 1/2" reducer into a 3/4" npt to 1/2" NPT reducer. I would have preffered to go right from a 3/4 reducer to a 1/4 reducer but they didnt have it in stock. So I had to make shift. However it all works the same, its just an extra fittng that you have to purchase. From that 3/4" reducer, it went into a 3/4" NPT, T fitting.

Out the bottom of the T fitting goes a 3/4" NPT nipple into the tank. On the other side of the T fitting, a 3/4" NPT to 1/2" NPT reducer, then into a 1/2" NPT to 1/4" NPT reducer. Out of the 1/4" hole goes the regulator that I took off of one of the compressors. This has an air preassure regulator, and a line cut off valve in one peice. I reccomend putting a quick connect nipple on the end of that, and a quick connect fittng (the one you pull back and slide on) to join the 2. I say this becuase there is no drain valve to remove moisture that collects in the tank. The moisture needs to be drained just like every other compressor. If you dont put the quick connect on, then you will have to remove the fitting by wrench every time. Spend the 2 dollars, buy a fitting, and be done with it. You connect your air line on to the end of the regulator.

Now, the great big tank gets charged by the 2 little compressors, thus giving me WAY more volume for extended air tool activity. The cfm capabillities also doube, now giving me 8.4cfm@90 and 10.4cfm@40psi.

Sure you can go out and buy a tank, with a say 5hp motor, and 30 gallon tank, and its gona cost you 550 bucks or whatever the cost may be. These compressors cost me 266.66 total (together) and they are pretty good for what they put out imo. The fittings were lets call it 20 bucks and the tank was free for me, but you can find tanks for free, usually the small ones just about anywhere. Even if you have to buy one, give it to your neighbour, let him use it in his bbq for a while until its empty and use a small one. Just use the fittings that fit it accordingly to make it work for your setup.. You can daisy chain tanks aswell for even MORE volume if needed.

I did have to remove the top cap that protects the valve to spin on all of my fittings. A word of advice, fill the tank RIGHT FULL with water before grinding off the protector. AND this is very important!! DO NOT GRIND THE WELD THAT HOLDS THIS PROTECTOR ON!!!! these tanks are preassure tested, and done so with this protector on. A lot of people will go to far with the grinder and remove to much metal, thus cutting into the tank and making it unsafe. I ground the protector off above the weld, so the weld seem is still there. I will probably remove it with a flap disc so its smooth, if I dont just put the protector back on in its spot that it was originally welding only ON TOP of the little tabs sticking off the tank. Weld quickly if you have to, but do not weld on the tank, tabs only. I thought the tank was emptied as it had been open for a few days and filled with water a couple times, so i stuck a torch to it. Residual gasses still lit on fire, and made one hell of a bang. However, do be sure that the tank is empty before grinding on it a little becuase its even worse when your face is over the opening and it goes off. This is why im saying fill it with water while grinding.

Tha tank will still stink of propane for a while, but it will clear out with the charging of the tank. AND make sure all joints are teflon taped (or thread sled with special sealent) for a leak proof seal. The best way to test is get it all set up, charge the tank to some sort of pressure, 30psi or 100 psi, doesnt matter, just something. Then pour soupy water over all of the joints, if it bubbles up, you have a leak. Then tighten or retape your joints if need be.

Pictures of this can be found here:

Its a clubphoto account so I cant put pics while I type, sorry guys.
Well, what do you guys think??


Weimer 02-28-2005 07:21 AM

I see 2 big no-no's with that setup.
1) There is NO safety popoff valve on the tank.
2) There is no drain on the bottom of the tank to drain the water(can you say rust?)

You spent $270 on that and you could HAVE bought a decent compressor for that price.Compressor
I am not trying to discourage you, but why take the chance with safety and reliability? Those compressors that you bought are designed to fill the tanks attached to them. If you burn them up eventually, don't be suprised.

adivito 02-28-2005 09:35 AM

i dont want to sound like a jerk but i agree with weimer. thats sounds cool and its great you did it yourself, but i just picked up an ingersoll 5hp 60 gal used for $200. look in your local papers or call some friends you would save yourself alot of time and hassle, and now you know what you are getting and it is totally safe. I have done things the hard way for a long time, and now i do it right the first time and it is alot better. and to top it off i wouldnt screw around with that propane tank, if it still smells there is probably fumes in there somewhere.

oldred 02-28-2005 10:22 AM

Here we go again! You have gone to a lot of trouble to accomplish next to nothing. You say that the bigger tank gives you WAY more volume to run your tools but that is just plain wrong! I know that some will just not accept it but it is a FACT! a bigger tank WILL NOT help your compressor keep up with a tool that is using more air than the pump is producing. The purpose of the tank is to control the on-off cycle rate and it is impossible for the tank to make a compressor produce more air. The common misconception here is that the tool will be running on stored air but that can not help because the avaliable stored air volume will be used in a VERY short time(usually a matter of seconds) when using somthing like a DA sander with a 10 CFM pump and a 60 gallon tank campared with a 30 gallon then you will have to wait longer for the tank to recharge so you gain nothing. You WILL see a big increase in performance if you just hook the two compressors togather but the propane tank is a lot of trouble for almost no benefit except to make life a little easier on the compressors. The bigger tank/volume myth is probably the biggest misunderstanding about compressors and is pushed by a lot of makers because the customer can see that big tank but they can not see CFM which is what runs your tools and is what really counts. Hook up the two compressors and you should have a usable set-up but do your self a favor and forget the propane tank or better yet take Weimer's advice and just get a bigger(CFM, not tank or "peak" HP) compressor. If you insist on using the set-up you described then Weimer also made two extremely important safety points that should be addressed immediately! I have been building and installing air systems for over thirty years and I have seen many things tried in order to increase air volume from an under-sized system but in the end the laws of physics ALWAYS win, there is just no way around it!

adivito 02-28-2005 12:06 PM

old red nailed it its cfm not capacity, Ive read alot of posts from oldred about this but no one seems to listen

goleafsgo_12 02-28-2005 03:24 PM

Ok, I do understand how a compressor works with hp, cfm, volume etc. I know that you dont get any more cfm capabillities with a larger tank, but you do get more volume. I dont have any air tools (sander etc) or need any air tools to run for a long period of time. I have a zippy wheel thing but that is just quick bursts anyways. The tanks on the compressors both have blow off valves at 130psi, so there is not 1, but 2! I got the tank compressor for cheap, and the propane tank was free. I just build go karts and ****, so i dont do heavy duty car work or anything. Its a hobby compressor, not a shop compressor. Its a great setup, and works perfectly fine. On the top of the tank, there is a quick connect valve where the air hose goes that I can drain with, its quite light and easy to flip every now and again. By the way, those are canadian prices, which makes a big difference.. you cant find a compressor with those stats and a decent size jug on it for anything under 400-500 bucks here (at princess auto, canadian tire, home depot, you name it)


CdnSoldier 03-31-2005 05:53 PM

I had a home build compressor and it worked great. The only thing is you will need a safety valve. You should doubleup for the tank. One compressor to run straight to the tank and one to run straight to you lines and then a Y to the tank. This will keep the tolls running.
To all, In Canada a good Compressor goes for 500$. The cheapest one I have found anyone can use is 350$ for a small hobby one. Our prices are 20-50% more.

ChevelleSS_LS6 04-04-2005 07:26 PM

not a bad idea, you wont need to run the compressors as often (frequency) but they will have to run longer. Also as said before, no drain in the propane tank.

39chevy 10-30-2011 08:46 PM

adding extra tank?
Weimer, quick question for you? How much do I gain with say my paint guns etc. by adding a 2nd say 40 to 60gal tank (to hold air of course) to my existing 5 hp 60 gal tank, single stage? Thanks, Dana. I know this post is over 3months old!

oldred 10-30-2011 09:53 PM


Originally Posted by 39chevy
Weimer, quick question for you? How much do I gain with say my paint guns etc. by adding a 2nd say 40 to 60gal tank (to hold air of course) to my existing 5 hp 60 gal tank, single stage? Thanks, Dana. I know this post is over 3months old!

Three months old? :confused: It's over 6 years old! :rolleyes:

As for your question I can easily answer that and this has been discussed to death already, you will gain exactly nothing! Think about it. if you double your capacity you will double the time before you run out of air but then you also double the time you wait on the compressor to catch up. If your compressor is less than a 100% duty cycle as most home types are then you can actually lose performance due to the pump getting hot from from the extended recharge times. When the pump is overheated CFM drops and so over a given work period you can actually lose run time as opposed to gaining anything. Sure it can be a help to have an extra couple of minutes of run time when painting but if you are running out of air now then you probably still will and running out at the wrong time with an extended recharge period could have serious negative effects, bad things can happen if you have to wait too long on air. Honestly I have seen this tried many times and the results were almost always unsatisfactory. It is a fact, a bigger tank does not make a bigger compressor and doubling the tank capacity on a compressor with less than a 100% duty cycle is going to seriously shorten it's service life due to the unreasonably long recharge vs cooling cycles that will occur every time it recharges. Doing this will be a mistake, you can have longer but fewer cycles or shorter but more frequent cycles but over any given work period your air supply will be the same regardless of tank capacity, that is unless the pump is overheated! You think waiting on it to recharge now is a bummer just try waiting on that pump to recharge 120 gallons!

The size of the tank is chosen by the manufacture to balance the run/recharge cycles and NOT to increase performance as is often mistakenly believed, that is not and never was the purpose for selecting a tank. Keep what you have your compressor will thank you for it by lasting longer!

39chevy 10-31-2011 09:58 AM

Thanks oldred, mine compressor as of now (pretty old) takes 60 seconds to fill back up to 120 psi then lasts for 1 min. and 45 seconds before it kicks from 90psi. I guess I will live with it. It's at a garage that is used strickly for painting, gets kinda loud, is there a muffler I can put on this thing? Thanks for the help, Dana

oldred 10-31-2011 10:42 AM


Originally Posted by 39chevy
Thanks oldred, mine compressor as of now (pretty old) takes 60 seconds to fill back up to 120 psi then lasts for 1 min. and 45 seconds before it kicks from 90psi. I guess I will live with it. It's at a garage that is used strickly for painting, gets kinda loud, is there a muffler I can put on this thing? Thanks for the help, Dana

With 5 HP and a single stage pump a 60 gallon tank is about right and if you really have to have more air then a bigger pump/motor for more CFM is about the only solution. As far as the noise you might try routing a hose from outside the shop to the intake on the pump. Doing that can sometimes make a difference because while the compressor may still be noisy it should be somewhat easier to live with. If possible it is best to place the compressor outside the work area because this not only eliminates or greatly reduces the noise problem it prevents the pump from inhaling contaminated air from painting, grinding, etc.

39chevy 10-31-2011 02:59 PM

Great idea's and solutions, probably go w/the hose cause the situation where the garage is, compressor has to stay inside, thanks again, Dana

RichardRonnie 03-13-2012 03:10 AM

You have provided great information about custom air compressor. Thanks for sharing this custom air compressor guide.

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