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1/2" or 3/4" shop air line?

Discussion in 'The Hokey Ass Message Board' started by Bobacuda, Aug 5, 2013.

  1. Bobacuda
    Joined: May 13, 2010
    Posts: 51

    Bobacuda
    Member

    Just finished installing a new air compressor in my garage and I noticed that the outlet from the tank would take 1/2", not 3/4" pipe. Does the diameter of the pipe matter to the air tools? Should I run 1/2" pipe or install an adapter and run 3/4" pipe?
     
  2. Mr48chev
    Joined: Dec 28, 2007
    Posts: 25,905

    Mr48chev
    ALLIANCE MEMBER

    3/4 would give you a bit more volume in the lines but I don't think you will gain much if any flow due to the 1/2 outlet on the compressor.
     
  3. Search Dog
    Joined: Oct 30, 2012
    Posts: 112

    Search Dog
    Member
    from Western CT

    They say to use the biggest you can afford. And a lot has to do with how long you are running the line, too.

    Yes, there will be a restriction in the fitting were it leaves the tank, but you have to think of the line as not just a conduit for the air, but it's volume is a small tank unto itself.

    I have a 5-hp, 220 volt compressor in my loading dock, and run a 3/4" to 1/2" to 3/8" down the 150 foot length of the dock. At the very end, where the trucks park, I cannot successfully run a 3/4" impact gun. It turns, but there isn't enough volume of air to give it enough torque to remove even a typical lug nut. The 1/2" drive impact guns and grinders and such work fine. If I need to use the 3/4" drive, I run a 1/2" hose to where the hardline is larger, bypassing the 3/8" section. That is the only restriction-caused problem I've ever run into. And the 3/8" line is lots smaller than the smallest you were considering.

    Check different locations on the tank. Mine has several bungs of varying sizes around the tank. The mainline comes off one side (via flex line), while my sandblast cabinet attaches to the other side through a regulator. The mainline has no regulator -- it's whatever the pressure of the tank is. The regulator gets installed at the end where the tools connect.
     
    Last edited: Aug 5, 2013
  4. 73RR
    Joined: Jan 29, 2007
    Posts: 6,241

    73RR
    Member

    Agreed! Run the largest pipe you can afford. Consider 1½" galv schedule 40.
    Ebay is full of fittings and valves.
    Check with your local plumbing/mechanical/industrial/irrigation/pump supply houses for pipe pricing. You will be stuck with 20-22 ft lengths and you might have to rent some threading equipment if you have odd lengths to run, but well worth the storage capacity.

    .
     
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  5. Koz
    Joined: May 5, 2008
    Posts: 2,185

    Koz
    Member

    I might add, the routing of the lines is critical to control moisture in the lines. Run them up high with 1/8" to the foot slope back to a drip leg with a ball valve at the compressor. Any condensed moisture will eventually end up there to be drained off daily. Each drop should also have a drip leg at the bottom and the ball valve to drain it. I have always been told air lines should be black iron not galvanized. Anybody know why?

    I like 1" laterals with 3/4" or 1/2" drops. Nothing smaller. Only use ball valves. the screw kind won't last the summer without corroding up. I use a large Ingersol-Rand with I believe and 80 gallon tank, and a Devilbis moisture trap. If you are going to spray paint off the same lines never run an oiler for your tools. Once the oil is in the lines it is impossible to get it all out and fisheyes are a way of life.

    Just my observations.
     
  6. Dane
    Joined: May 6, 2010
    Posts: 1,353

    Dane
    Member
    from Soquel, CA

    If you only plan to run one air tool at a time 1/2" is fine.
     
  7. stimpy
    Joined: Apr 16, 2006
    Posts: 3,547

    stimpy

    chek to see if the tank bushing is removeable , if it is you can up size the outlet on it , when I had the shop ( trucking co) we ran a 1 1/2 line out as a feeder with 1" drops for out hd impacts ( which used a chicago twist fitting ) and had smaller qc hook ups for air lines , the tool room were they did repair work on smaller stuff and car work we used a 1/2 line. and always try to run a filter on the lines if you use any type of ferrous pipe to catch rust , scale and sometimes galv flakes. copper isn't as bad but its expensive , and NEVER USE PVC for one its not rated for air/gas usage and 2 .its deadly when it breaks from the shrapnel . and not worth the risk !
     
  8. Del Swanson
    Joined: Mar 27, 2008
    Posts: 709

    Del Swanson
    Member
    from Racine, WI

    NEVER run galvanized pipe for air line! I'm going to hear you've done it for bla bla years and never had a problem. Small bits of the galvanizing can break off and clog small orifices in air tools and become projectiles out of a blow off tool, usually when you're blowing the dust out of your face. Use sch 40 black pipe, or sil flossed sch K copper (never sch "M" drain copper). If you have the pipe pitched correctly and enough drains and dirt legs you won't have a problem with rust. The bigger the better for mains. the drops can be 1/2" or 3/4".
     
  9. Fordtudor37
    Joined: Jan 5, 2011
    Posts: 273

    Fordtudor37
    Member

    I ran 3/4 inch plastic pipe with threaded connectors for the air fittings from my compressor all around my 24x24 garage. Glued everything together and did not spare on the glue, so far 22 years with no leaks and I have run all my tools. It runs from compressor to water separator to plastic lines around garage.
     
  10. mike in tucson
    Joined: Aug 11, 2005
    Posts: 485

    mike in tucson
    Member
    from Tucson

    The flow is approximately the square of the diameter difference so 3/4" pipe flows 2.25 times what a 1/2" pipe flows. A 3/8 dia air hose also flows 2.25 times a 1/4" ID hose... these are for equal length runs. For longer runs, the bigger pipe is better.
    Rapidair has a decent chart http://rapidairproducts.com/flowrate.asp
     
  11. 28TUDOR
    Joined: Jan 25, 2007
    Posts: 419

    28TUDOR
    Member


    Same here, I run 120psi the pipe is rated at 500psi. No problem in 12 years.
     
  12. Del Swanson
    Joined: Mar 27, 2008
    Posts: 709

    Del Swanson
    Member
    from Racine, WI

    Plastic gets brittle over time, especially if there are airborne chemicals or oil in the space. I've personally seen the aftermath of PVC failing (using extra glue does no good as most failures aren't at a glue joint) and you do not want to be around when it does. You've been lucky for 22yrs
     
  13. mechanic58
    Joined: Mar 21, 2010
    Posts: 681

    mechanic58
    Member

    I have a friend that ran a 4" sch 40 PVC header in his shop and used 2" sch 40 for all the drops. He did the math - I forget how much it increased his storage capacity, but it was a lot. Really reduced the frequency of run time on his compressor too. He did this about 15 years ago - its still in service with no issues.
     
  14. mike in tucson
    Joined: Aug 11, 2005
    Posts: 485

    mike in tucson
    Member
    from Tucson

    4" PVC in Schedule 40 has a water working pressure of 220 psi at 73deg F. At 100 deg F it derates to 136 psi. PVC pipe is a bomb when handling gasses. UV light deteriorates the stuff.
     
  15. mechanic58
    Joined: Mar 21, 2010
    Posts: 681

    mechanic58
    Member

    His is probably operating up to about 120 psi - its inside a climate controlled building and has been in working service for 15 years. No issues. Many people have done this.
     
  16. 270dodge
    Joined: Feb 11, 2012
    Posts: 674

    270dodge
    Member
    from Ohio

    I have used 1/2 inch plastic in my shop for 30 years with no problems. It is rated for 400 plus pounds. The first 40 feet is copper all slanted toward the compressor(zig zag style) to act as a water separator. Black iron pipe is required for gas installs because it has few defects. Galvanized is used to seal the defects.
     
  17. Offset
    Joined: Nov 9, 2010
    Posts: 1,613

    Offset
    Member
    from Canada

    I am just about to hook up my new compressor so I appreciate this conversation. I think I will go with 3/4" black pipe and take advantage of the suggestions offered.
     
  18. JEM
    Joined: Feb 6, 2007
    Posts: 1,041

    JEM
    Member

    My home shop/garage has 3/4in blue (L) copper for the main runs with 1/2in drops.

    Black iron rusts and can be a PITA to work with.
     
    Last edited: Aug 5, 2013
  19. txturbo
    Joined: Oct 23, 2009
    Posts: 1,771

    txturbo
    Member

    black pipe is not a good idea in my area.....to much humity....copper or galvanized is the only way to go. Mine is 3/4" rubber hose from the tank to the wall then its copper for about the first 10 feet then galvanized 3/4" and I have about 40' of sloped run that goes outside my garage then comes back inside for the first takeoff...all are off the top and go up 6" then turn down for 12" with a ball valve drain. The long run lets the metal pipe cool the air and condense the moisture out.
     

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