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  #1  
Old 07-24-2008
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Teflon tape for Seacock/thru hull fittings

Question, I was wondering if you should use teflon tape for the thru-hull male fitting to the female seacock fitting which are NPS? I assume you will use it on the opposite side of the seacock the NPT fitting? What have you all done as far as teflon tape for the fittings?
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Old 07-24-2008
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Ok..

Before I answer the question I must speak to safety. It is NOT advisable to mix NPT (tapered pipe thread) with NPSM (straight pipe threads). This can be a dangerous mismatch leaving only a few mis matched threads between your boat sinking and floating.

That being said many boaters are out there sailing and floating on mismatched threads and many boats sink due to failed bellow waterline fittings.

You can make NPT to NPS fittings not leak but you need to be careful in your tightening and be sure not to over tighten or under tighten. It is always advisable to use a proper flanged and bolted thru-hull but if you don;t have the funds or time NPT to NPS can be used.

To seal these threads do what any GOOD pipe fitter does and use both Teflon tape and pipe dope. ONLY apply the tape and dope to the male threads. Apply the tape first then brush on some pipe dope. I like Hercules Pro-Dope and the thicker YELLOW gas grade teflon tape. Both are available at Home Depot..

Please be cautious and know that mis-matching threads is not a good idea especially bellow the waterline...

Mismatched threads - NPS/NPT on left NPT/NPT on right:


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halekai36,


Thanks for the response but I am not mismatching threads, I bought a groco sea **** and a thru hull. The flanged seacock base has a female nps the thrull which will be mated to the the seacock is male nps. I was wondering if you use teflon tape for the NPS fitting?

http://www.defender.com/product.jsp?path=-1|51|106370|813148|319675|860855&id=860619

http://www.defender.com/product.jsp?path=-1|51|106370|316448|315121&id=992827

links to what i bought.

Last edited by saurav16; 07-24-2008 at 03:23 PM.
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I plan to use teflon tape at my female seacock to male barb thread junction.

Quote:
Originally Posted by saurav16 View Post
Question, I was wondering if you should use teflon tape for the thru-hull male fitting to the female seacock fitting which are NPS? I assume you will use it on the opposite side of the seacock the NPT fitting? What have you all done as far as teflon tape for the fittings?
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pipe dope, pipe dope and more pipe dope
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Originally Posted by saurav16 View Post
halekai36,


Thanks for the response but I am not mismatching threads, I bought a groco sea **** and a thru hull. The flanged seacock base has a female nps the thrull which will be mated to the the seacock is male nps. I was wondering if you use teflon tape for the NPS fitting?

http://www.defender.com/product.jsp?path=-1|51|106370|813148|319675|860855&id=860619

http://www.defender.com/product.jsp?path=-1|51|106370|316448|315121&id=992827

links to what i bought.
Sorry I misunderstood that you had a flanged adapter.

That side of the flanged base gets what ever bedding compound you choose to use. The head of the mushroom makes the seal and you simply wipe 4200 or Sikaflex 291 on the threads, and generously around the head, and screw it in.

You also bed the underneath of the flange. You are not creating a water tight seal with the NPS threads and the seal is at the flange base, you'll note a groove around the thread insertion point, and the mushroom head. The marine sealant does help to keep it water tight but really the threads could go in dry if you have done everything else right..
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Old 07-27-2008
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Kinda curious as to why there are two different threading standards (?) for the same application? If NPT threading can make a water-tight seal, but NPS threading not, why ever make or use NPS threading in this application?

Asked and answered: Seacock & Thru-Hull Primer/Pre Information. Thanks, Hal!

Jim

Last edited by SEMIJim; 07-27-2008 at 02:08 AM. Reason: Found the answer to my question
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Old 07-27-2008
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I've been using Locktite 565 with good success. It's teflon dope, but it's extra gooey. I have done fittings from air to gas to water with nary a leak.
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