RE: [PSUBS-MAILIST] Tapered Threads

["James Frankland" <james@guernseysubmarine.com>]

Hi Hugh/Emile/Jim

Thanks for advice on the threads.  I have found out from Swagelok that there is a corresponding copper gasket that i need.  You would have thought the fitting would have come with the gasket included.  But anyway, 2 gaskets ordered and the problem is solved.  Straight thread, copper gasket.  I can continue with construction of the tank.

http://www.swagelok.com/search/product_detail.aspx?part=CU-8-RG-2

Thanks
James


----- Original Message -----
From: Hugh Fulton [mailto:hc.fulton@gmail.com]
To: personal_submersibles@psubs.org
Sent: Mon, 20 Oct 2008 10:51:08 +1300
Subject: RE: [PSUBS-MAILIST] Tapered Threads

Hi James,
Just a word of caution on your threads.  Swagelok use and have a number of
threads so you should check whether they are BSP parallel, NPT or SAE.  A
common one is the SAE threads which use O'rings and special fittings and are
not to be used with BSP or NPT.
Cheers, Hugh


-----Original Message-----
From: owner-personal_submersibles@psubs.org
[mailto:owner-personal_submersibles@psubs.org] On Behalf Of James Frankland
Sent: 19 October 2008 23:18
To: personal_submersibles@psubs.org
Subject: [PSUBS-MAILIST] Tapered Threads

Hi All.

Can anyone help me with this minor thing.

I'm making the VBT and i had the threads cut on a special threading machine.
See this picture.

http://guernseysubmarine.wordpress.com/

Anyway, the 1 inch valve has a tapered thread, so i have cut the thread on
the pipe accordingly to have the same taper.  It fits perfect and will screw
up nice and tight.

But, the little 1/2 inch swagelok fitting has a straight thread inside.  So
i cut one end of the pipe tapered thread and the other straight.  Im not
sure which to use.  If i screw on the tapered thread, it will tighten up but
i'm nto sure if thats right as i feel its only tightening on the end of the
taper.  But if i use the straight thread, it screws down right to the end
and is it going to seal properly?  I feel as if there should be a rubber or
fibre washer in the end of the swagelok fitting to seal the straight thread.
There isnt one but i can make one easy enough.

Any ideas?  Taper or non taper.  Washer?

Thanks
James



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