Home made air compressor

Old 08-02-08, 11:30 PM
Thread Starter
Join Date: Aug 2008
Posts: 3
Received 0 Votes on 0 Posts
Post Home made air compressor

Hi all,

first time poster here.

I have acquried a collection of air compressor motors and tanks, and want to use them all together.

I spray cars/bits of cars as a hobby. I need about 10 CFM for the spray gun, and about a further 8 CFM for an air-fed mask to keep me safe!

This is what I plan to do:

Here are my questions:

1) Will it work?! I know that this is not the professional way to do it, but will it work?

2) Will I get any benifit in using larger diameter copper piping between the tanks? I was planning on using 1/2inch.

3) What kind of CFM output can I expect? Is it as simple as the sum of all the individual compressors?

4) Is there a way of estimating the free air delivery? The CFM figures I have I think are piston displacement, and I understand that there will be a drop between CFM and FAD.

thanks all,

Old 08-03-08, 04:08 AM
Join Date: Oct 2005
Location: USA
Posts: 274
Received 0 Votes on 0 Posts
I not a painting expert but couldnt the air you breath be on a blower system or canisters mask. Your using a lot of air for that breathing system for a hobby painting shop.
I see no need for the last 2.5 hp compressor as you have already met your CMF needs for your gun and air breathing. I do think the additional big tank is a good idea as it will keep the compressors from cycling so often.
I have never heard of FAD. All I have ever used was CFM. I would think FAD would have to do with pipe sizes and valves.

Old 08-03-08, 06:19 AM
Join Date: Nov 2005
Location: North Carolina
Posts: 948
Received 0 Votes on 0 Posts
1. yes
2. use 3/4" but don't lose any sleep over it. consider the quick connects and thier I.D. specs as restrictions in any system you design.
3. it is the sum of all unless any of the units won't cycle because of the delivery of another.
4. cfm by displacement is an age old trick of compressor manufacturers to sell size over performance, but i think you would be fine with the 3 and 2 hp units alone. you may not even need the storage capacity you've illustrated.
Old 08-03-08, 07:45 AM
chandler's Avatar
Banned. Rule And/Or Policy Violation
Join Date: Dec 2005
Location: USA
Posts: 39,964
Received 6 Votes on 6 Posts
One compressor will furnish the CFM you need for painting. What you need is Volume, and the additional tanks will provide that. I wouldn't use copper at all to connect the tanks. Use Airquip. If one of the tanks moves slightly, it could crack the copper connection. Airquip will allow for movement.
Old 08-03-08, 08:27 AM
Thread Starter
Join Date: Aug 2008
Posts: 3
Received 0 Votes on 0 Posts
Thanks for the replies idmason60and flopshot.

Part of the reason for using the mask is it's what I have! But I understand your point. I think the air flow into the mask is at quite a high flow rate to be at positive pressure to the surrounding area, to force paint fumes away from you.

I thought about using the additional pumps because firstly, I had them, and secondly to reduce the work each one does. the 2.5hp pump on the 50l tank is a less industrial unit (direct drive, but oiled), and the extra tank space would make the other pumps work harder.
I also am sure that I have read somewhere that the CFM quoted is not the CFM you get (this is the free air delivery think I think), so I want some overhead as well.

My plan is to use the pumps as such:

1) Turn the power on! The three pumps all kick in and have built in cut-offs at 160psi.
2) Set the regulator to 90psi - to give me enough pressure to feed the mask and have about 25psi at the gun (when trigger pulled)
3) Spray away!
4) At some point, the motors will kick back in (I think they are designed to do this when pressure in the tank is less than 100psi.
5) Then, the three motors together should still provide me enough constant CFM to breath/spray, plus some surplus to recharge the tanks. This means they won't duty cycle at 100%, which I think would shorten the life of the lot!
6) Surplus output from the motors eventually refils the tanks to 160psi, and all the motors cut out. I (hopefully) will not have noticed a thing!

I will use 3/4 inch pipe, but I understand your point about other places in the system where there are bigger restrictions to air flow. Is regular copper pipe ok?

I will put some pictures up as I do it!

any more suggestions then let me know

Old 08-03-08, 05:20 PM
Join Date: Oct 2003
Location: PA, USA
Posts: 748
Received 0 Votes on 0 Posts
Couple of things to think about: 1) unless you run all the motors off the same starter and pressure switch, they may not all cycle together. I would wire it so only 2 pumps cycle and 1 is on stand by in case the pressure in the tank ever gets below 95 psi. 2) as a painter you have to be concerned about the quality of air getting to your gun and your lungs. I hope you are not spraying oily moist air right out of the tank. Other than that, good plan and good luck.
Old 08-04-08, 01:59 AM
Thread Starter
Join Date: Aug 2008
Posts: 3
Received 0 Votes on 0 Posts
Thanks chandler and Markiz37

I will try to find some airquip piping, Is it available from hardware stores?

I have an oil and water filter on the line, and a mini water filter just before the gun. There's also a biological filter or something on the belt of the respirator, so I hope I'm covered.


Thread Tools
Search this Thread
Ask a Question
Question Title: