NPT verses NPS....

[NYSail]

So I found one of my in-line ball valves that connects to my anchor wash-down was broke. Handle moved giving the impression it was in fact working, however lever was broke and stuck in open position. So without thought I went and bought a new Groco in-line ball valve which has NPT threads. Then got to thinking (novel idea!) and remembered that the threads may be different... and yes they are.... straight thread NPS (Beneteau). So I have two options here..... get a new NPS in-line ball valve or replaced the through hole fitting to match the NPT. I kind of like the idea of changing the thru-hull fitting as its not a big deal and it would mean a critical part is new. But was also wondering..... is one thread style better than the other?

Thanks!

Greg
s/v Souleil

 

[py26129]

I have read nothing, including Mainesail, that indicates the one thread is better than the other. The key is that the threads are matched on the thru hull and the seacock and that both are high quality pieces.

Matt

 

[LeeandRick]

If you go with an NPT on the thru hull fitting (probably find only NPS) it will not screw all the way into the valve if the valve mounts to the thru hull. Double check your valve it may have NPS on one end and NPT on the other. The seacock I just bought is like that.

 

[Ariel]

Greg,

Leeandrick is correct. The thru-hull fitting is a straight thread. A tapered thread will only engage about three threads on a straight thread. Strength and safety is the issue. Here is a West Marine article about this.

www.westmarine.com/WestAdvisor/Seacocks

It could be that the seacock you have has strate threads on the inlet side.

Dave

 

[Gunni]

GROCO now makes a line of bronze valves with straight threads that have the proper pitch to fit the Beneteau thru-hull fitting. I believe they refer to them as ‘euro valves’ and they work beautifully, thread way down on the straight thread thru-hull. I used one last year to replace my galley sink drain valve. You may need to contact GROCO tech support to get the right part number. Way better solution than jamming a NPT to a NPS or replacing the thru hull.

 

[CYQK]

Few years ago I replaced evrything in the hull with Groco stuff
Groco is the best stuff out there
Sourced the stuff from a commercial supplier not West Marine retail and had thread problems with the ball valves and the thru hulls
Took a while to sort it all out supplier was not happy to have to return all
Felt like i had invented a problem what a pain in the ass!!!!
Hope the have sorted all this out now ask a lot of questions and get proper answers before pulling the trigger
Good investment good luck!!

 

[shemandr]

I had this problem on my Ranger 29. NPS vs. NPT - I think the thru hull was straight and the ball valve was tapered. I was surprised that such a discrepency could exist but I gather it is common. BTW the surveyor didn’t note it.

 

[Maine Sail]

Beneteau uses BSPP threads. You can't slap an NPT ball valve onto a BSPP thru-hull as it is not just a NPT to NPS mismatch it is a complete thread compatibility mismatch.

Groco is now the main supplier to both Beneteau US and EU. They have a whole line of BSPP thru-hulls and valves and tailpieces specifically developed for BSPP equipped vessels. Beneteaus installation is still not ABYC compliant for strength standards, in the smaller sizes, but at least they finally addressed to poor metallurgy problems and now offer a true bronze product on their boats not a brass......

 

[njlarry]

I think the best solution is to use Groco adapter plate fittings. One side is nps for the mushroom the other is npt for the ball valve. Another big advantage is the valve can be easily replaced without removing the thru hull. I believe that this is detailed on MS marinehowto.com web site. I replaced all mine.

 

[DougM]

Beneteau uses BSPP threads. You can't slap an NPT ball valve onto a BSPP thru-hull as it is not just a NPT to NPS mismatch it is a complete thread compatibility mismatch.

Found out that little fun fact the hard way the first year I had my boat. The sink drain ball valve was left closed ovet the winter, and naturally it froze and split. The new valve I got wouldn’t thread into the thru hull. The only solution I could come up with at the time was to disassemble both valves, and use the new upper half and ball cock on lower half of the original. It works, but I would not have done it in salt water because of the dissimilar metal situation.

 

[Gunni]

Yes, thanks Maine Sail, that is exactly what I used on my Beneteau, the GROCO BSPP valve. They have the proper thread “pitch”. British Straight Pipe Pitch (BSPP).

One other thing I noted was the reason the galley sink ball valve failed - it was a hollow ball valve. A small leak allowed it to fill with sink water and when the temp dropped it froze and cracked. GROCO makes solid ball bronze valves.

 

[Ron20324]

Gunni, it has been a few years, but I went over to the part lady at AYS*Benny dealer) and got the OEM valves. NPT one side, NPS the other.

 

[BigEasy]

Any suggestions as to where the bspp valves & thru hull fittings can be ordered? A quick search didn't locate a source. Perhaps they need to be special ordered. Would like to change out some of the Beneteau oem valves & thru hull fitting when I haul out this spring.

 

[Gunni]

GROCO sells them direct.
GROCO.net

 

[BigEasy]

Thanks Gunni; couldn't find them at any of the main chandleries.
Are the female threads atop the ball valve ( where the tailpiece attaches), NPT or do you have to use a BSPP threaded tail piece?

 

[Gunni]

The threads on both ends are BSPP and GROCO makes BSPP fittings that fit them. I was going to a hose and got the barbed fitting. The fitting valve and thru hull all thread very deep, maybe ten threads. Use plenty of thread tape or dope to tighten them up, they are not self-tightening like NPT / NPT fittings.

I have a recollection of ordering them from Jamestown Supply or Defender after I got the part numbers from GROCO. Wanted to promote better availability at the chandlery and as I remember the were a bit less expensive.

 

[BigEasy]

Thanks for the info on the Groco BSPP fittings----I didn't even realize that they existed. I will finally clean up the Beneteau OEM mess that has brass valves and probably miss matched fittings also. I would prefer to use Maine's recommendation to use the Groco adaptor base; however, there isn't enough room at most of my thru hull locations. I know that the ball valve atop the thru hull fitting isn't the best; however, using that configuration with matching components will be an improvement. Plan use FRP backing plates also as the present factory configuration has none.
I was able to download Groco's catalog and the BSPP fittings and part numbers are clearly listed. Good idea Gunni, I will call Defender to get a price as these fittings are not in the Defender catalog. Main & Gunni, again thanks for the info and advice---Once again SBO comes thru!