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Old 06-27-2009, 11:00 AM
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Originally Posted by shad9876
My compressor is going to be about a hundred feet from the shop and I am trying to determine the best way to get the air from the compressor to the work area.

I am thinking of running 3/4" black iron pipe underground from the storage shed that houses the air compressor to the shop.

What do you think? Could I get by with 1/2" pipe, or am I undersized with 3/4" for that length?

Any suggestions welcome!!
You didn't say what your compressor rating was... HP &/or CFM. Assuming about 5HP, I'd suggest 1" galvanize pipe minimum.
For less than 5HP, �" minimum. For such a long 100' run, you may need 1" to prevent a severe pressure drop.

Choosing the correct size of air-pipe:

This compilation might help ---> DIY Series ~ Tools: Air-compressor & Piping Installation

Here are some things to keep in mind ---> Air Compressor Piping Diagrams and Tips.
Originally Posted by Keith Dickson -
Air Compressor Piping Rules Of Thumb:

After leaving the air compressor, air line pipe goes straight up the shop wall as high as possible.
This helps minimize any water from leaving the compressor and traveling through the pipe.

Slope main lines at least four inches (10 cm) per 50 feet (12.7 m) of pipe away from air compressor so
that condensate travels with the flow of air and away from the compressor.
As warm air leaves the compressor, it cools and thereby condenses as it travels through the pipe.

This water vapor, a problem in itself, can also cause scaling and rusting inside the piping.
Install drop legs for condensate removal.

The first air drop should be at least 25 ft. (6.4 m) from the compressor although 50 feet (12.7 m) is optimum.
This allows the compressed air to cool to room temperature so any condensation can occur before it gets
into the water separator.

Take-off comes from the top of the main air supply line at each air drop.
This reduces the risk of water and other contaminants from traveling down the drop into the water separator.

Use carbon steel pipe as discharge pipe material. Never use PVC or ABS. (PVC is easy to work with, but will not allow the hot air to cool quickly enough to condense the water in the compressed air.
Also, in case of a compressor regulator failure, if the PSI inside the line were to go above the rated safety capacity, the plastic pipe won't just split, but will actually explode, producing razor-sharp projectiles which are sure to damage property and person.)

Consider using Schedule 40 black iron, galvanized, copper, stainless steel, or anodized aluminum.

Size the pipe for maximum CFM required. This will equal full load production plus future expansion plans.
(See chart above)
My $0.02
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