Antenna Launcher, A Warning

There seems to be a sudden interest in pneumatic launchers for installing antennas. These things are also known as air cannons. antenna launchers, or even potato guns. They are very easy and inexpensive to build. There are many references on the Internet for just how to do that.

Schedule 40 PVC pipe and fittings are the preferred construction material. It is readily available, easy to work with, and assembly is only slightly more involved than gluing things together. The only problem is, though, that Schedule 40 PVC comes in two basic flavors. One is for the “supply side” carrying water under pressure, and the other, the “drain side” for waste and water removal and vents.

To highlight the difference between the two, the pressure rated PVC versus the DWV (drain/waste/vent) PVC, a 3″ Schedule 40 pressure rated PVC pipe is rated to withstand 260 psi of pressure. On the other hand, 3″ Schedule 40 DWV PVC is rated to withstand 0 psi.

That’s right: DWV PVC is not rated to withstand any pressure whatsoever. ZERO psi.

Any sensible antenna launcher operator will likely use between 30 and 75 psi of air pressure to fire an object over even the tallest tree. That is well within what any pressure rated PVC pipe or fitting would handle. It is also well beyond where DWV PVC is safe. This is not to say that a DWV PVC antenna launcher will explode the first time you use it. It shouldn’t. But if and when the plastic material does fail, it is quite catastrophic, explosively splintering into shards that can cause serious injury or death. The strength of PVC decreases with age, exposure to ultra-violet radiation (for example sun light), and use (much more so with compressed air than with water).

So, how do you tell the two PVC types apart? Anything pressure rated should have “NSF pw” or “NSF pw-G” printed or stamped on it. DWV PVC should say “NSF DWV” and should be avoided. Some of the pipe at or below 2″ carries a dual-rating and may be marked “NSW pw-G-DWV”.

Lowes and Home Depot do sell pressure rated pipe in the smaller diameters. Some Home Depots may have 3″ and 4″ short sections of pipe bearing the “NSF pw” marking. Neither store stocks fittings much other than DWV fittings. As it turns out, however, Grainger and McMaster-Carr can provide all the necessary fittings and at a very good price (in most cases better than the home-improvement stores).

Here’s a video of someone “doing it right”:

At the risk of the following video being misinterpreted, I’ll ask you pay attention to how remarkably DWV PVC fails (with shards) and the magnitude of the failure pressure below that of NSF pw-G. Again, too, PVC strength decreases with age, ultra-violet radiation (e.g., sun light), and use.

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