[PSUBS-MAILIST] Pressure Transducer

Thu Dec 29 20:13:29 EST 2016

Hi Alan,
Sloppy threads (especially fine straight ones) on Chinese HP fittings are a
bit scary - perhaps a good idea to stand (extremely) well clear and
pressure test with an extra full tank.

Using adaptors could get things working, and may be more possible than
getting your Chinese company to re make the transducers, although I vaguely
recall you were against using adaptors in the first place.

I also just had a thought that if you pot them, you may need to account for
the ambient pressure being higher than normal. Ie. Under normal
circumstances it acts as a differential pressure sensor, relative to the
(ambient) pressure on the back of sensing element. When you pot them, the
reference pressure may change.

Cheers,
Steve

On 30 Dec 2016 8:01 am, "Alan James via Personal_Submersibles" <
personal_submersibles at psubs.org> wrote:

Cliff,
just looked up the GL rules regarding gas penetrations & they are a bit
ambiguous
in this instance, as are ABS.
GL section 9, B 1.2 ... Pipes which are led through the pressure hull wall
are to be
fitted with two shut-off devices, one of which is to be located immediately
at the hull
wall.
   You could argue that a pressure transducer shuts off the gas flow at the
hull
penetration anyway. I just think that in my instance, with a small cabin,
it is best to
keep the high pressure lines away from it.
Alan

------------------------------
*From:* Alan James via Personal_Submersibles <personal_submersibles at psubs.
org>

*To:* Personal Submersibles General Discussion <personal_submersibles at psubs.
org>
*Sent:* Friday, December 30, 2016 8:08 AM

*Subject:* Re: [PSUBS-MAILIST] Pressure Transducer

Cliff,
I looked at machining but they wouldn't fit in my lathe.
I was specific about what I ordered and the manufacturer has got
it wrong. I have been talking with them & I'll send them back.
   I am trying to keep as close as practicable to GL rules.
They require a valve  at  the hull for any gas coming in to the
cabin. Although there is no gas lines coming in & through the cabin,
I would be pretty sure they would require a valve between the hull
& the pressure transducer. With 6 tanks to monitor, this will save
on the cost of 6 valves, but more importantly will save space inside
the hull, & as these valves would need to be clustered within arms
reach, that space in that area would be an important saving.
Also, as I have said previously, a failed o-ring on the hull interface
with high pressure air / O2 could lead to a fatal condition in a small
one person submersible.
Cheers Alan

------------------------------
*From:* via Personal_Submersibles <personal_submersibles at psubs.org>
*To:* Personal Submersibles General Discussion <personal_submersibles at psubs.
org>
*Sent:* Friday, December 30, 2016 3:33 AM
*Subject:* Re: [PSUBS-MAILIST] Pressure Transducer

If it were me I would machine out the conical section and then machine off
enough of the 10mm threaded shank until it will mate.

Actually i would abandon this approach altogether and put the pressure
transmitters inside the boat and use Swagelok fittings and ss tubing to
connect to regulator.

O-ring seals are designed for high pressure.  Likelihood of leak into boat
is small.

Cliff

Cliff Redus

On Dec 28, 2016, at 8:58 PM, Alan James via Personal_Submersibles <
personal_submersibles at psubs.org> wrote:

Hank,
yes it has a hole down the middle of the threaded fitting.
I only have 10mm of thread. I could machine a few mm off the end but still
wouldn't have a flat area to squash the o-ring against. The female fitting
is slightly
tapered initially, & the o-ring is meant to fit in to this taper.
If I put a nut on as a spacer, the internal face of the o-ring would be
against the thread,
& high pressure air could leak down between the thread & nut.
Alan

------------------------------
*From:* hank pronk via Personal_Submersibles <personal_submersibles at psubs.
org>
*To:* Personal Submersibles General Discussion <personal_submersibles at psubs.
org>
*Sent:* Thursday, December 29, 2016 3:15 PM
*Subject:* Re: [PSUBS-MAILIST] Pressure Transducer

Alan,
I assume the threaded shaft is just a means of attaching it with a hole in
the middle.  If so, file it shorter,  put a nut on the tread first and the
nut will fix the end of the tread when you remove it.
Hank

On Wednesday, December 28, 2016 6:47 PM, Alan James via
Personal_Submersibles <personal_submersibles at psubs.org> wrote:

Just received my 6 pressure transducers from China.
These were tailor made for me to fit in to the high pressure port
of my first stage regulator; So rather than have high pressure air
& oxygen coming through the hull wall, I just have wires.
   Unfortunately it looks like they have got it wrong. They have a conical
portion at the base of the male thread that makes it impossible to seal
with an O-ring. I specified 10mm for thread & shank, but the 3mm extra
on the conical portion means the flat faces of the pressure transmitter &
regulator can't meet. Other than that it looks ideal for potting the wires.
   Any suggestions for a fix on this, other than sending them back?
I could possibly turn the conical portion down & stack washes under the
o-ring. The fit was also a bit sloppy, but so was the original plug that was
in this high pressure port. Not sure if this is normal or not.
See attached photos, thanks.
Alan

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