PVC & CPVC are "no nos" for compressed air, brittle failure is possible.
but it looks like PEX is ok
http://66.102.7.104/search?q=cache:ZmkdIs7L7_YJ:
formatting link
Tuesday, January 04, 2005 The introduction of PE tubing or pipes GENERAL Polyethylene (PE) is a thermoplastic material produced from the polymerization of ethylene. PE plastic pipe is manufactured by extrusion in sizes ranging from ? to 63". PE is available in rolled coils of various lengths or in straight lengths up to 40 feet. Generally small diameters are coiled and large diameters (>6" OD) are in straight lengths.Polyethylene can be used in low temperatures (0 F or colder) without risk of brittle failure. Thus, a major application for certain PE piping formulations is for low-temperature heat transfer applications such as radiant floor heating, snow melting, ice rinks, geothermal ground source heat pump piping, and compressed air distribution. CODE STATUS PE pipe is recognized as acceptable plumbing piping for water services, drainage, and sewer applications in most model plumbing codes. Verify acceptance and installation of PE piping systems with the local code enforcement authorities having jurisdiction. AVAILABILITY PE pipe and fittings are available from plumbing supply houses and various hardware retailers throughout the U.S.A. and Canada. PE pipe is generally less expensive than metallic piping materials. MARKING PE pipe must be labeled as follows:
1.The manufacturer's name or trademark
2.The standard to which it conforms
3.Pipe size
4.Material designation code (PE 2406 or PE 3408)
5.DWV if for drainage piping
6.Pressure rating if applicable
7.DR number or Schedule number
8.If the pipe is for potable water, a laboratory seal or mark attesting to suitability