RE: [PSUBS-MAILIST] Pipe System Confirmation.

I love rules of thumb, and this is a keeper. But is this one based on the expectation of a cylindrical shape? What also makes me think rules could go out the window is that these things have all sorts of intersecting volumes at right angles. Plus threads, which must offer wonderful stress concentration.

From: owner-personal_submersibles@psubs.org [mailto:owner-personal_submersibles@psubs.org] On Behalf Of Hugh Fulton
Sent: Tuesday, March 13, 2012 5:10 PM
To: personal_submersibles@psubs.org
Subject: RE: [PSUBS-MAILIST] Pipe System Confirmation.

Alec, As a rule of thumb you can make anything for high pressure (4000 psi) if you have the wall thickness 1/8 of the outside diameter.

Or if you are wanting a certain ID then divide ID by 5 and you will get the wall thickness. Not exactly but safe enough.

The other is the ID is 75% of OD , even simpler. This also applies to the thread so if you are using ¼ NPT then ID is the outside of the male thread.

Cross holes are where you need a bit of wall thickness. For ¼” manifolds use 1” square bar. ½” use 1-1/2” bar. Use brass it is so much faster. Hugh

From: owner-personal_submersibles@psubs.org [mailto:owner-personal_submersibles@psubs.org] On Behalf Of Smyth, Alec
Sent: Wednesday, 14 March 2012 7:58 a.m.
To: personal_submersibles@psubs.org
Subject: RE: [PSUBS-MAILIST] Pipe System Confirmation.

Hi James,

What a timely email. I’m in the process of making a HP manifold for Snoopy. I was making it out of 316, because I happened to have just the right bit of material in my cutoff bin, but tapping all these NPT threads in 316 is an absolute “wax on, wax off” experience. I did about 300 cycles of tapping and eight of a turn and cleaning my tap with a toothbrush and then, as invariably happens at the end of the very last thread, I broke the tap and there’s absolutely no way it’s coming out. I’ve ordered a new piece of 303 so I can tap them more easily on the second attempt, because 316 is a bear.

I have no idea what thickness you will need, and there’s more to it than just the thickness, since it’ll also depend on things like shape and stress concentrations. In general I don’t think this is something one can calculate, but the idea is to drill the central chamber as small as you can so there is minimal interior volume, and make it pretty massive. My new manifold (3000 psi) is basically a ¼” hole drilled longitudinally in a 1.675” hex bar.

But I wanted to mention I have another old SS manifold lying in my parts bin that may work for you. It was part of Snoopy’s original configuration and was made by Dale Heinzig. This manifold ran only 175 psi, but who knows, you could test it at the higher pressure and see if it cracks (with water please, not air). The wall thickness is about ½”. It has two chambers. The first has two 1/2” NPT threads and one 1/8” NTP. The second has one 1/2” NPT, one 1/4” NPT, and one 1/8” NPT. It would be easy to drill through connecting both chambers together if you wanted. Nothing fancy, but if you have a use for it, I’ll happily donate it to your project.

Personally I wouldn’t use the 1^st stage gauge port, it has a TINY orifice which is intended to read pressure but not provide any meaningful flow. I’d skip the reg entirely and just put a yoke on the tank.

Thanks,

Alec

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From: owner-personal_submersibles@psubs.org [mailto:owner-personal_submersibles@psubs.org] On Behalf Of James Frankland
Sent: Tuesday, March 13, 2012 1:41 PM
To: personal_submersibles@psubs.org
Subject: [PSUBS-MAILIST] Pipe System Confirmation.

Hi All.

1. Does everyone else keep getting spam messages from Scott Waters?

2. I have finalised my HP air system. Ive probably made a meal out of something relativly simple but i havent ever built a HP system like this before so have had to figure it all out.

The system will be designed to route as per K350 design but use swagelok fittings and run at higher pressure. The system is designed to opperate at a max pressure of 1000 psi but will run normally at lower. Most of the system will be 1/4 inch pipe, with just the variable tank inlet\vent part 1/2 Inch.

The limitation on the design is the worcester ptfe sealed ball valves which have a maximum working pressure of 1000psi (69bar).

I have 2 last questions.

1. I have decided to use worchester ball valves (466TSE ptfe sealed) instead of the diaphragm valves or even needle valves. Do you think this will be ok?

2. Does anyone have any suggestions for the thickness for my 300bar manifold.

I am going to make a 4300psi (300bar) stainless manifold to accept the tanks.

The manifold will have 2 x standard scuba quick release high pressure hose fittings. Like you would use for a BCD or gauge off your 1st stage. This means i can run 2 tanks to the system but be able to get them on and off easily and quickly.

There will be a 300 bar gauge attached to the top of the manifold to measure manifold inlet pressure, a manual relief valve off another port and then the outlet which will go to a 300bar - 70bar pressure reducing regulator with inline gauge to measure system pressure.

Emile says that the HP port on a normal 1st stage does not give a lot of flow, so i am going to just run it and see if its enough. If not, i can pipe the manifold directly to the tanks.

The idea with this is that 1, the 2 x tanks can come off easily and 2, i have adjustable high pressure outlet.

Sorry, after all that, the question is. Any suggestions for thickness of the manifold to hold at 300 bar? I think i might go to my local dive shop and measure the thickness of their filling station manifolds. hmm, good idea.

Thanks as always,

regards

James

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