Re: [PSUBS-MAILIST] Tapered Threads

["Jim Kocourek" <kocpnt@tds.net>]

Hi James,

While not an expert, I have quite a bit of experience in this area. Many of 
our hydraulic and 3000 PSI paint fittings are using straight threads. In all 
cases they use either an o-ring or gasket to seal at the base. Depending on 
the design of your fitting you may be limited to a gasket, because unless 
the fitting has a concave area for the o-ring the rubber will probably 
squish out upon final tightening.

I just received the heads for my hard ballast tanks on Friday and will begin 
building mine as soon as I locate proper tubing for the straight portion of 
them.

Best Regards,

Jim K

----- Original Message ----- 
From: "James Frankland" <james@guernseysubmarine.com>
To: <personal_submersibles@psubs.org>
Sent: Sunday, October 19, 2008 5:17 AM
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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