Sizing air lines and the output size from compressor tank

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Old 07-30-13, 08:20 AM
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Sizing air lines and the output size from compressor tank

So I have this new-to-me, excellent-condition air compressor. I'm giving it the thorough inspection and I notice that the bung for the output pipe is huge, but the hole tapped into it to receive an NPT connection is small, 3/8" NPT to be precise.

Now I'm trying to figure out if there would be an advantage to having a larger output, like 1/2" NPT or 5/8" NPT, what size lines for the system would be best for a given hole through the bung, etc. Currently my hose reels are 3/8" NPT with rubber hoses, and the current delivery system that must be replaced is 1/2" PVC pipe.

Basically I'm at a point where I can redo the whole thing from scratch and should do just that to get rid of the plastic.

I plan to hang several hose reels and regulators, and right now the furthest compressed air drop by pipe distance will probably be about 70' away. I'm considering also running a drop to a garden shed that's much more distant though, and would be probably 150' away by pipe distance. Yes, I would put a ball valve in to shut that drop off when it's not actively needed.

I've already pulled the tank drain, I could easily enough drill and re-tap to 1/2 NPT or 5/8 NPT if it would be beneficial to do so. I'd just have to blow compressed air from the old-going-away compressor through the bung to push the junk from drilling and tapping out through the bottom of the tank.
 
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Old 07-30-13, 09:25 AM
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If it was mine I would remove the reducer and replace with a new one, not tap it out. At least 1" FPT would be best.
Here's how a real air system should be plumbed.
Air Piping Layout

Far to many times I see people try and plumb an air system as if it was a water supply system. There completely different. Your trying to keep moisture out of the lines not make it easier for it to get to the tools it's being used on.
Black iron is the correct material to use for the lines.
Copper slimes up on the inside that will go right through a filter.
Galvanized tends to flake tiny particles.
How ever rust from black iron will be filtered out.
Time and time again I see people slope the lines toward the tank, wrong. How's water going to run back toward the tank with 80 PSI + forcing it down line? It needs a drip leg that can be drained.
 
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Old 07-30-13, 11:52 AM
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I was under the impression that it would be near-impossible to get that reducer out, and it would also be difficult to get any replacement to seal up well, hence considering tapping it.

I may just go with 1/2" lines. The ID of L copper is similar to the ID of the 3/8NPT fitting, so there won't be a nozzle-type behavior.
 
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Old 07-30-13, 12:10 PM
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Have you had this compressor running? Are you sure that this bung is for the supply line? Although large for an unloader line, it looks like it was intended for something like that; or maybe a tank drain. How many horsepower is the compressor? As Joe said, for the kinds of run that you mentioned, a 1" line would be most appropriate, maybe 3/4", but that would be borderline, in my opinion. An air tool, especially at 70' or more down the line, can drop the pressure in the line quicker than the compressor can keep up.
 
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Old 07-30-13, 03:06 PM
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This is definitely the output line, about 2/3 of the way up the side of the tank. The drain is at the bottom underneath and I had to put the compressor up on wood blocks to make it practical to remove. I'm going to add one of those automatic water drain valves down there when I have a chance.

Compressor is 4.7HP, 14CFM at 90PSI if memory serves.
 
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Old 07-31-13, 10:10 AM
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auto drain

Don't waste your money, put a simple 1/4 turn ball valve there. Simple and reliable.
 
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Old 08-01-13, 06:37 AM
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Do not use copper lines!
Green slime, it will work harden and may break off.
 
 

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