[PSUBS-MAILIST] Pressure Transducer

Thu Dec 29 15:55:55 EST 2016

Cliff,just looked up the GL rules regarding gas penetrations & they are a bit ambiguousin this instance, as are ABS.GL section 9, B 1.2 ... Pipes which are led through the pressure hull wall are to befitted with two shut-off devices, one of which is to be located immediately at the hullwall.   You could argue that a pressure transducer shuts off the gas flow at the hullpenetration anyway. I just think that in my instance, with a small cabin, it is best tokeep 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 gotit 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 thecabin. 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 saveon the cost of 6 valves, but more importantly will save space insidethe hull, & as these valves would need to be clustered within armsreach, 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 stillwouldn't have a flat area to squash the o-ring against. The female fitting is slightlytapered 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 portof 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 conicalportion at the base of the male thread that makes it impossible to sealwith 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 theo-ring. The fit was also a bit sloppy, but so was the original plug that wasin this high pressure port. Not sure if this is normal or not.See attached photos, thanks.Alan
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