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Old 05-10-2009, 02:23 PM
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moe1942 moe1942 is offline
Voice of Experience
Join Date: Jun 2004
Location: Alexandria, Louisiana
Posts: 11,033

Originally Posted by Lu47Dan View Post
Sizing the mains
In sizing the mains in a Compressed Air Piping System I am prejudiced against 1/2" copper tubing . It has more restriction then 3/4" copper tubing . It is fine for drops and drip legs but I frown on using it for mains . Also it has limited future expansion possibilities . There are various formulas out there that will tell you when you have reach the flow limit of a certain sized tube but they are way too complicated for this discussion .
In that I mean you put up 1/2" mains for your 3Hp compressor and they work swell for inflating tires and running a impact once in awhile , but a few years later you get a killer deal on a 5hp compressor and want to add air hungry equipment like a bead blast booth , pot sandblaster , etc . The 1/2" lines become problematic . with a pot sandblaster you are probably running at least 50' of 3/8" hose to get it away from the shop . The combined total of the main and the hose are more like 100' . Adding length to any air line adds resistance to it .
In the long run starting with 3/4" copper tubing makes monetary sense . You purchase the tubing once .
Sizing drops , all drops are not created equal . For standard air tools and air nozzles a 1/2" drop will be more then adequate , for air hungry applications a 3/4" drop works better . In my own shop I run dedicated a dedicated air chuck for my bead blast booth with another air chuck to run air tools from . This saves wear and tear on chucks and also saves time when I need to do a quick blast job .
Drip legs . when installing drip legs I add a valve above the leg and about 12" below the tee for the air chuck . The drip leg is usually 12" long or long enough to stop just inside the height of a five gallon bucket . The valve is operated then closed to send any condensate into the drip leg . There are a few ways to terminate a drip leg in a copper system , one a C X MNPT and a cap , a C X FNPT fitting with a plug or a C X FNPT fitting with a petcock .
When selecting plugs and caps for the drip leg , buy brass and used teflon tape on the threads.
I prefer C X FNPT fittings with a plug .
  1. C = Copper tubing size
  2. MNPT = Male threaded
  3. FMPT = Female threaded
  4. F = Fitting sized that end
The next several installment will be on fitting terminology , or how not to look like and idiot while purchasing copper fittings :evil: .

Moe , I am figuring on several hijacks before this thread is finished .

Dan I just couldn't help myself. Want me to delete that???
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