E27 original thruhulls are NPT or NPS?

[timh]

My new-to-me E27 has gate valves. Could be the originals I suppose. They'll need to be replaced. I've been reading through the messages here about thruhulls, gate valves, and seacocks. As I understand it, thruhulls and seacocks connect with a straight thread (NPS), while one of the issues with gate valves is that have a tapered thread (NPT). Do I have that right? If so, are the original thruhulls also NPT or was there a thread mismatch at the outset, with NPS thruhulls connected to NPT gate valves? Just curious.

- Tim H.

 

[Emerald]

The thru-hulls on my prior E-27 were all straight thread, with gate valves. As I think about it, I've never seen a thru-hull that wasn't straight thread. Never bothered to figure out the thread on the gate valves since I replaced everything from the thru-hull, backing pad, seacock, hose etc.

 

[Loren Beach]

Many years ago, I was sold some taper-thread bronze ball valves by a supposed marine vendor... so be careful. You do want straight thread IF you are going to screw a *separate valve* onto a thruhull fitting.
(OTOH my experiences may not be typical.)

If starting over, why not go for the preferred and much stronger choice and simply install a flanged sea cock? That way you have no separate valve screwed onto a weaker threaded casting..

Loren

 

[timh]

Thanks for the advice. I do intend to replace the gate valves with seacocks. In fact that's why I've been reading everything I can find about thruhulls and the different sorts of valves that can be attached to them. But I am considering the option of not replacing the thruhulls. My cleaning diver says they look great from the outside, and I can't see anything wrong with them from the inside. Of course if those original thruhulls were NPT then they would definitely have to be tossed out with the gate valves. It sounds though that the thruhulls are very likely NPS, so I at least have the option of keeping them. I am still curious though about whether the gate valves are NPT or NPS. Is the difference visually apparent? If so, when I take the gate valves off, I'll check them.

- Tim H.

 

[Gary Peterson]

The gate valves would be NPT as would the ball valves.