can you mate marelon seacock to bronze thru hull - SailNet Community
 
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can you mate marelon seacock to bronze thru hull

can you mate marelon seacock to bronze thru-hull? I understand that all marelon fittings are NPS and the bronze seacock is nps as well. Any thoughts?
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post #2 of 9 Old 06-22-2008
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Don't, marelon isn't nearly as strong as bronze for seacocks - the last thing you want is a seacock breaking at sea. With bronze all you have to worry about is electrolysis.

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post #3 of 9 Old 06-22-2008
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even though the same size, the threads are different. the thru hull is streight thread the valve is tapered. they should be connected with an adapter plate. Check out this Boat Projects Gallery Photo Gallery by Maine Sailing at pbase.com
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Quote:
Originally Posted by saurav16 View Post
can you mate marelon seacock to bronze thru-hull? I understand that all marelon fittings are NPS and the bronze seacock is nps as well. Any thoughts?
If you have an NPS marelon ball valve, which is rare, and an NPS thru-hull NO you can not mate these two together!

Yes they WILL go together but NPS-M threads are "mechanical" only as in NPS-M, M for mechanical. Mechanical threads, are not, and were NEVER intended to seal against positive pressure or to be water tight!

NPT & NPT (tapered) threads mate together to SEAL OUT, (or in) water!! NPS & NPT is a dangerous mis-match but it will, sort of, seal out water..

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Last edited by Maine Sail; 06-22-2008 at 05:09 PM.
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The other problem is that you probably shouldn't put a plastic seacock over a metal through-hull since metal tends to expand and contract more than the plastic will.

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Halekai will edit his post to reflect that the valve has NPT threads and then it will make sense to you as well as being correct. badsanta is correct in that you need an adapter coupling to go between the two types of threads.

As Dog suggests, do not ever put a female plastic fitting over a male metal fitting. This practise causes flooded basements in houses where there is no motion and little vibration. Imagine what could happen on your boat. If you are to use metal and plastic together, the plastic should always be the male fitting and held in compression. Otherwise, while you may get lucky and crack the plastic during installation, giving you a warning that you're not conducting a good pipefitting exercise, the plastic will most likely appear just fine until it fails at the worst possible moment. Instantaneously you'll be reduced to pounding a tapered wooden plug in it-assuming you carry them-or an amazement at how fast water can flow through such a relatively small hole.

If you're to mix and match doing this the proper procedure would be to put a plastic nipple into the Marelon valve (I recommend Schedule 80 and do not get the cast and then threaded nipples-get one that is turned. The cast nipples will have either lands on their side or you'll see a tiny seam from the casting running down them and they are substantially weaker than a turned nipple made of Sked 80 PVC.). Then that nipple can be threaded into a female NPT to female NPS adapter to complete your installation.

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Sway-

Some of the marelon ball valve seacocks are NPS threaded, but they're generally not sold in the US.

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The marelon valve sold at West marine is NPS on both ends

West Marine: Marelon Flanged Seacocks Product Display

Also Haleki all thru hull nipples are NPS only the groco ball valve has an NPS base and and NPT threaded top.
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Obviously, through hulls have to be NPS or you couldn't cut them to length. Halekai is well aware that through-hulls are NPS, as he states on his photo essay on through-hull installation.
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Originally Posted by saurav16 View Post
The marelon valve sold at West marine is NPS on both ends

West Marine: Marelon Flanged Seacocks Product Display

Also Haleki all thru hull nipples are NPS only the groco ball valve has an NPS base and and NPT threaded top.

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her going when she oughta fall down, tells you she's hurting 'fore she keens. Makes her a home.

—Cpt. Mal Reynolds, Serenity (edited)

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