Copper Boiler Construction?

[robert egglestonParticipant @roberteggleston16335]

Would like to hear from some experienced copper boiler builders. Currently starting to build a CliShay type boiler designed by the late Robert Maynard of Cincinnatti, Oh. His boiler plan for a 4" dia. water tube boiler design indicates outlets for steam appliances like PR valve, Pressure gage, Steam supply, whistle etc. calls for Bushings going into openings to support these items are tapped 3/8-24, one top of boiler opening bushing calls for a 1/8 th NTP thread. Question is which thread is more appropriate and will seal the best? Should you use the straight thread 3/8-24 with a suitable pipe sealant or use a NTP type thread that seals on a taper fit? Any wisdom and advise on this subject would be appreciated. Regards. Bob E.

[robert egglestonParticipant @roberteggleston16335]

Thread size for bushings supporting boiler output connections

[Simon CollierParticipant @simoncollier74340]

It is traditional to use ME threads and BSB threads on boiler bushes. Typically I use 1/2 -26, 3/8 -32, 5/16 -32, 1/4 -40 and 3/16 -40. Bigger threads such as 9/16, 3/4 would be 26 also. Taper threads are not necessary, but ultimately you can use whatever you wish within reason.

[David George 1Participant @davidgeorge1]

Hi Robert If you use taper bushes you will have to use taper fittings which will entail either buying a taper die, or taper screw cutting to make your own or buy taper fittings which are not so available.

David

[JasonBModerator @jasonb]

Robert is in the US so ME threads and matching fittings are likely to be hard to find so stick with the American UN  threads.

American practice also tends to use a lot more threaded pipe rather than the more common nuts and nipples used in the UK.

Edited By JasonB on 10/12/2018 09:03:33

[Carl Wilson 4Participant @carlwilson4]

NPT threads do not seal on the taper. There is a leak path around the threads.

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