> -----Original Message----- > From: [email protected] > [mailto:[email protected]] On Behalf Of Joseph M Gwinn > Sent: Tuesday, July 07, 2009 5:21 PM > To: Discussion of precise time and frequency measurement > Su > > The relevant US pipe-thread standards are quite clear - > straight threads are for mechanical connections only. For > connections that must also contain fluids under pressure, one > uses taper threads such as the ubiquitous NPT. Over the > decades, I have lived in many houses, including my current > house, with circulating hot water heat and cast iron > radiators, and I have never had to redo a radiator > connection. I've never had a leak, and most of these systems > were old when I bought the house. > > If you have straight pipe threads going into radiators, there > is an installer who should be made to re-do the job. Maybe > he was an out-of-work electrician, and used rigid electrical > conduit for pipe. >
Rigid conduit uses tapered NPT threads. NEC 344.28 Reaming and Threading. All cut ends shall be reamed or otherwise finished to remove rough edges. Where conduit is threaded in the field, a standard cutting die with a 1 in 16 taper (3/4 in taper per foot) shall be used. BUT, IMC (a thinner wall conduit) is tapered at 3/8"/ft (1 in 32, half the taper of standard heavy wall rigid conduit) because the wall is about half the thickness). And, of course, since the female thread in the fitting is almost certainly tapered at the 1 in 16, the half taper IMC will thread in and tighten up with a bit less thread engagement. Straight threads are found on bolts, and on the threaded part of compression fittings (the kind with a crushable ferrule around the tube), and on some gas fittings (where there's an O-ring or other gasket for sealing). I'm not sure if a gas fitting like a CGA-580 (which has a NGO-RH thread) is tapered, even without a gasket. Actually, there's a bewildering variety of standard threads, tapered and not. Some tapered threads are designed to seal without a filler, some with. Not only that but the actual thread shape is different (55 vs 60 degrees). Fortunately, for the average hacker, if it's close, and the metal is malleable,.... > Straight threads and O rings are seen only in hydraulic > systems, not domestic water or heating systems, and the > mating parts have correctly designed pockets to hold the > O-rings. And they do not use jam nuts. One screws them > together until they bottom. > > Joe Gwinn > > _______________________________________________ > time-nuts mailing list -- [email protected] To unsubscribe, > go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
