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Old 04-12-2012, 07:29   #106
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Re: Brass Seacocks -

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Originally Posted by Stumble View Post
Bill,

Thru hull fittings should never be screwed directly into ball valves. You really need a mating flange between the two. In fact they aren't even designed to fit together.

Thru hulls are all designed with strait threads so they can be cut to length once they are installed. While ball vales almost always have tapered threads that create a better seal. The flange is there not just to spread the load, but also to act as a mating adapter between the two thread types.

It sounds like you are missing the flange, which would explain why you are having issues. Matching strait and tapered threads is done all the time (you can usually get 3-4 turns) but is always a mistake.

BSP parallel and taper threads are designed to go together and regularly do in all forms of plumbing , The tapered thread is designed to provide the sealing unlike parallel thread joints where some other sealing is required.

However the proper process is for the male thread to be tapered and the female end to be parallel. This allows for positive engagement and progessive thread binding. Unfortunately on threaded skin fittings, with a threaded nut/flange, this isnt possoble and the threads have to be parallel. A male parallel into a female taper, results in early binding and is leak prone.

Theres no easy solution using threaded skin fittings. Id suggest either parallel to parallel and use PTFE or other tapes. At least there is good thread coverage this way. Female taper to male parallel can result in few thread being engaged and often needs tape to seal it anyway. Worst of both worlds. really in parallel threads there should be a O-ring seal

BTW most of european valves are BSP parallel.

I know why its done, a bronze skin fitting and bronze ball valve combination is about 40 quid, a sea cock is 150+ quid.


Dave
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Old 04-12-2012, 07:48   #107
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Re: Brass Seacocks -

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I can't see any markings on the ball valve in question. It's in a difficult location. The other two valves (head inlet and sink drain) in the head are marked DW 20 and FN 30, respectively. They have a symbol that looks kind of like a diamond with a bar across the center.
This is a DIN standard valve, generally to DIN 3357, its must contain on the body a size marking DNxx and a pressure marking PNyy and a manufacturers trade stamp. On valves greater then DN50 , a materials designation must also be stamped.

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Old 04-12-2012, 08:45   #108
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Re: Brass Seacocks -

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Originally Posted by goboatingnow View Post
BSP parallel and taper threads are designed to go together and regularly do in all forms of plumbing , The tapered thread is designed to provide the sealing unlike parallel thread joints where some other sealing is required.

However the proper process is for the male thread to be tapered and the female end to be parallel. This allows for positive engagement and progessive thread binding. Unfortunately on threaded skin fittings, with a threaded nut/flange, this isnt possoble and the threads have to be parallel. A male parallel into a female taper, results in early binding and is leak prone.

Theres no easy solution using threaded skin fittings. Id suggest either parallel to parallel and use PTFE or other tapes. At least there is good thread coverage this way. Female taper to male parallel can result in few thread being engaged and often needs tape to seal it anyway. Worst of both worlds. really in parallel threads there should be a O-ring seal

BTW most of european valves are BSP parallel.

I know why its done, a bronze skin fitting and bronze ball valve combination is about 40 quid, a sea cock is 150+ quid.


Dave
Not in the US. NPT mates to NPT (tapered to tapered). NPT is not intended to mate to NPS.. Will they seal, yes, you can get them to but it is a band aid at best..

In the US the ABYC specifically prohibits mismatched threads being used, but it does not seem to stop most people.....

NPS to NPT on left and NPT to NPT on right....

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Old 04-12-2012, 08:49   #109
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Re: Brass Seacocks -

Australia we use predominately BSP same story, Hence if it's an issue run it down with a tap or die depending on situation.

Avoiding what your excellent pic's show. Nice work.
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Old 04-12-2012, 09:11   #110
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Quote:
Originally Posted by Lagoon4us
Australia we use predominately BSP same story, Hence if it's an issue run it down with a tap or die depending on situation.

Avoiding what your excellent pic's show. Nice work.
You can't fix it with a tap LOL
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Old 04-12-2012, 09:15   #111
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Re: Brass Seacocks -

Sorry you maybe not understanding, you use a plug tap either tapered or parallel to change the thread to what your after.

Same for the thruhull you can convert a parallel thread to tapered by running a die-nut down it.

It 'aint rocket science. cheers
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Old 04-12-2012, 09:42   #112
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Re: Brass Seacocks -

It's far better to use a parallel thread for fittings under pressure hence if the valve has a tapered thread (internal) it's easy to run a plug parallel tap into it to straighten/match to the parallel that you are fitting it to ie in this case parallel thru-hull. (I don't recall ever seeing a tapered one)

Does that help?
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Old 04-12-2012, 10:39   #113
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Re: Brass Seacocks -

Thanks for the information on DIN standards. I did a quick check online and haven't found a source just yet but I'll look more carefully this evening when I have time.

Also, I (now) know the difference between NPT and NPS and appreciate how one might fix things (kludge). I think that the next time I haul out I'll replace all thru hulls, seacocks or whatever we call them.

I hate to say it, because I am philosophically against the concept, but right now I'm trying to get a good fix for one ball valve and I'll risk the others. They look pretty good but I now appreciate that they are likely old enough that they should be replaced for safety sake. The right fix will be to replace them all using the methodology in MaineSail's "How To" articles Compass Marine "How To" Articles Photo Gallery by Compass Marine at pbase.com

I'm going to have to write up this whole repair project because it has a lot of lessons. At least for me, it did.

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Old 04-12-2012, 11:07   #114
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Re: Brass Seacocks -

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Originally Posted by Bill_E View Post
I hate to say it, because I am philosophically against the concept, but right now I'm trying to get a good fix for one ball valve and I'll risk the others. They look pretty good but I now appreciate that they are likely old enough that they should be replaced for safety sake.

Bill
Sounds a lot like what I'm doing. I looked at my valves and they look good but all backed with wood... Until I got to the raw water intake that was loose, so I'll replace that one now. I'm considering to replace all the other ones in the boat just for safety sake too even though I could probably get away with keeping them the way they are for now. It's going to be a costly project to replace all of them (I have 8 total) but the peace of mind will be nice too. I'll eventuallly write up my work on my blog when it's done for the first one I do.

Good luck on yours.
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Old 04-12-2012, 14:50   #115
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Re: Brass Seacocks -

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Originally Posted by Lagoon4us View Post
Sorry you maybe not understanding, you use a plug tap either tapered or parallel to change the thread to what your after.

Same for the thruhull you can convert a parallel thread to tapered by running a die-nut down it.

It 'aint rocket science. cheers
NO !!


The wall thickness of most skin fittings/thu-hulls was never designed for a tapered thread to be cut into it. I have had this exact conversation with Conbraco and Groco, two of the largest US suppliers of skin fittings. This is not sched 40 or sched 80 pipe they are bronze machined castings designed for a straight thread and "full flow".......

Manufacturers will sometimes offer a "combination thread" version which is simply shaving the peaks off the threads of a straight threaded thru-hull in order to get a few more threads of insertion.

With a "combination thread" the thread valleys are NOT made any deeper, and this does not sacrifice wall thickness, only the peaks are shaved. This too is a band-aid but slightly better than NPS to NPT.


Cutting tapered threads into thru-hull fittings can drastically weaken them beyond their already pathetic strength when you've threaded a ball valve to them. If you want to do this PLEASE consult your skin fitting manufacturer.

The nominal wall thickness of many off the shelf skin fittings, in the 1" size, is no thicker than a US penny or about 1.5mm. Cutting this any thinner.. well.......... Good luck...
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Old 04-12-2012, 17:28   #116
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Re: Brass Seacocks -

YES!! we are talking about cutting a parallel thread into a ball valve to remove a taper to match a parallel thread on a thru-hull.

Cheers
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Old 04-12-2012, 18:43   #117
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Re: Brass Seacocks -

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YES!! we are talking about cutting a parallel thread into a ball valve to remove a taper to match a parallel thread on a thru-hull.

Cheers

I was responding to this statement by you:

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Same for the thruhull you can convert a parallel thread to tapered by running a die-nut down it.
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Old 04-12-2012, 21:38   #118
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Re: Brass Seacocks -

Whatever theories are advanced here in this thread, I am learning a great deal of useful information, which is not always the case.

I do not resent my technical ignorance being made apparent to me. I welcome the opportunity to learn, particularly when it involves nice big holes in the boat I will be calling home.
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Old 04-12-2012, 23:14   #119
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Re: Brass Seacocks -

Whatever skin fittings you guys have is not the point, in no circumstance should a thruhull be fitted with a reduced wall thickness of 1.5mm in my lifetime i've never seen such a thin wall.

My whole and complete point is this:-
1) Any matching thread can be converted by the use of a tap or die parallel to tapered and vice-versa.
2) A parallel thread should be the only one used in a thru-hull situation simply because it seals best with compound and not by thread binding.
3) Thru-hulls of 1.5mm wall thickness (likely in the thread area i guess) are a furphy in this discussion and should not be on a boat let alone modify.

Cheers
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Old 05-12-2012, 05:09   #120
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Re: Brass Seacocks -

I managed to find the DIN standard. It’s actually DIN 3357-4 for nonferrous ball valves. It turns out that in the sizes of interest to me, there are three possible threads, including NPT. I will just have to get some pipe and see if it’ll thread easily into the ball valve in place. I hope it’s NPT because I’m going to have a hell of a time finding the others.

Regarding wall thickness, Thanks to MaineSail!! I understand that when you cut the thread you reduce the wall thickness of the starting pipe. I suppose that when buying thruhulls one should look for those with a “thick” wall and suffer the loss in ID. Better to have some flow restriction than a weak system.

Now, what is the downside to using an NPS tap and cutting the thread in the ball valve to match the NPS thruhull? It doesn’t seem that this would drastically reduce the wall thickness because the ball valves already have pretty thick walls. I guess this falls into the category of “good enough” until I haul out and redo everything according the best practices.


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