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One of the best discussions and formulas that I have seen for designing compressed air piping may be found in the link below. Basically, you are aiming for an air velocity below 20 feet per second in the main header, and 30 feet per second in drops. If the price of copper and hassle of steel causes you to seek a plastic alternative, one options is Pex-AL-Pex. This is a sandwich of cross linked polyethylene and aluminum. It is commonly used for radiant heat. The (offshore) manufacturers suggest its use in compressed air service, although I don't know the status of regulatory approval in this country (OSHA). From an engineering materials point of view, cross-linked polyethylene has a high energy of fracture. As with steel or copper, it will fail by splitting, rather than shattering like PVC. (PVC has a low energy of fracture -- it is brittle like glass or eggshells). I personally feel comfortable using Pex-Al-Pex in a farm shop environment, but would not even consider PVC. With employees I'd be constrained by OSHA regardless of the physics. All plastic materials are inferior to metal in terms of effectively cooling compressed air and condensing out moisture. Rubber or vinyl air hoses tacked up on the wall are the worst of all from this aspect. (The thermal conductance of copper is 1000 times higher than plastic, a fact which the copper tube institute is happy to trumpet in their literature) The actual practical difference in heat transfer between metal and thin-wall plastic is not that bad, due to the "skin effect". In order to transfer heat from compressed air to the surrounding atmosphere, you must first transfer it from the compressed air to the inner pipe wall, thence through the metal pipe, thense from the outer pipe wall to the surrounding air. The total thermal resistance is the sum of these 3 effects. So even though the copper itself is very conductive, the overall system effect is only about twice as good as Pex or Pex-Al-Pex tubing. (This is why Pex is used in radiant floors). PVC and ABS are thicker wall and lower thermal conductivity and I believe end up about 1/4 that of copper. Truck brake hoses are worse yet, and reinforced vinyl or rubber air hoses truly terrible. You can compensate for the degraded cooling in the header by using a longer length (to the first drop) or higher diameter or both. Alternatively, the first 50 feet could be run in copper or steel.
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