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RE: [PSUBS-MAILIST] gas piping through hull

In theory you could go either way on that. In practice, I've found it easier and cheaper to go with NPT threads on the through-hull itself and use Swagelok fittings with female NPT threads on them.  By doing this, you can for instance just drill and thread your own SS through hulls out of solid bar stock to make them uber strong. There are NPT-threaded Swagelok fittings of all kinds, or NPT to Swagelok adapters. If you look on eBay, you can generally find a few people selling Swagelok fittings BY THE POUND. Get yourself a few pounds of predominantly common sized fittings, like quarter inch. Every sub builder needs a large jar full of Swagelok stuff. That approach will cost a tenth of what it would to just buy individual fittings brand new on an as needed basis.
 
 
:)

Alec 
 



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From: owner-personal_submersibles@psubs.org [mailto:owner-personal_submersibles@psubs.org] On Behalf Of Brian Cox
Sent: Tuesday, January 15, 2008 11:03 AM
To: personal_submersibles@psubs.org
Subject: RE: [PSUBS-MAILIST] gas piping through hull

Does the threaded stainless steel nipple that is being welded thru the hull need to be a Swagelok type fitting ?  or are these just standard pipe threads on a schedule 80 stainless nipple which the Swagelok then attaches to.
 
Brian
-----Original Message-----
From: owner-personal_submersibles@psubs.org [mailto:owner-personal_submersibles@psubs.org]On Behalf Of Cliff Redus
Sent: Monday, January 14, 2008 4:16 PM
To: personal_submersibles@psubs.org
Subject: Re: [PSUBS-MAILIST] gas piping through hull

Swagelok SS fittings are top of the line in US for gas fittings and yes they are expensive.  I used Swagelok for all the 1/4" gas and 3/8" hydraulic tubing connections on my boat.  You can get Swagelok on Ebay at a substantial discount.
 
Cliff
 
----- Original Message ----
From: Antoine Delafargue <antoine.delafargue@gmail.com>
To: personal_submersibles@psubs.org
Sent: Monday, January 14, 2008 12:39:16 PM
Subject: Re: [PSUBS-MAILIST] gas piping through hull

Thanks guys for your great insights!
 
If I find already machined pieces with sufficient thickness, I will probably go for individual through hulls. Perhaps female threading allows having sufficient nipple thickness with no flow restriction. I will calculate the structural reinforcement I need in my case. Perhaps some valves exist with male threading?
 
The plate option was primarily to keep the structure simple (fewer welds, simpler machining, endcap not punched like a stamp by a dozen holes), considering I had to do the machining. 
I don t expect changes (but who knows...), but in any case I plan to mount the whole endcap on a flange bolted to the rest of the sub.
 
About the leaky threading, I was impressed by the design of Swagelok tube fittings, which made me have doubts about more conventional NPT male/female assemblies (like in the K boats) with teflon tape or the like. What do you guys use? Swagelok seems expensive.

Antoine

 
On 1/13/08, Dan. H. <jumachine@comcast.net> wrote:
With a male thread coming through the hull, the emergency shut off valves screw right on to them instead of having to add a nipple. 
 
Dan H.
----- Original Message -----
Sent: Sunday, January 13, 2008 7:04 PM
Subject: Re: [PSUBS-MAILIST] gas piping through hull

 
Hi All,
 
This may sound like a dumb question, but why use a male pipe nipple thru the hull as compared to a female threaded nipple. It seems to me that the female thread would have much less chance of being damaged for two reasons. 1. the threads are internal. 2. The nipple can protrude less because of it's length. I understand that the threads inside the coupling will distort with welding, but would think that this is easily remedied with a tap.
 
Can anyone comment? Am I missing something?
 
Thanks in advance.
 
Best Regards,
 
Jim Kocourek
----- Original Message -----
From: Dan. H.
Sent: Sunday, January 13, 2008 7:51 AM
Subject: Re: [PSUBS-MAILIST] gas piping through hull

 
Antoine,
I agree with Frank.
Keep it simple. 
 
For through hulls that are a permanent part of the sub, something you must have to operate and will never move, just drill through your hull and weld in schedule 80 stainless steel pipe nipples (male thread).  On the interior, install an emergency valve on each of them where they pass into the hull. 
 
For through hulls you may later change or for room to add more, install a stainless steel disk in a housing similar to what a view port would be.  That way any changes you want to do later can be done on the disk and your not burning and welding on the finished hull.
 
Dan H.
----- Original Message -----
Sent: Sunday, January 13, 2008 2:57 AM
Subject: Re: [PSUBS-MAILIST] gas piping through hull

 
Hello Antoine. I prefer the '' welded pipe'' design but have seen the ''threaded hole'' design and both seem to work fine. I am  using 3/4 inch stainless nipples welded into the hull, with a ball valve on the inside, and compression fittings leading to the inside manifold or outside ballast tanks.
My thought is that the fewer connections, the lower the risk of leakage.
Depending on the anticipated depth, the nipples can be sized to withstand whatever pressure you have.
A schedule 80 fitting can take lots of pressure, and should it be necessary later to replace it, it can either be re-threaded or cut out and replaced quite easily and cheaply, versus a female thread assembly which would be a little harder to fix. Frank D.



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