[PSUBS-MAILIST] Dive report: Snoopy at Seneca

Tue Jun 9 18:46:19 EDT 2015

Alec,I had a look at the specs on that link. Thanks.The 3/8" ID x 5/8" OD X 1/8" tube is rated for 40psi internal pressure.As this is for fuel there could be a safety margin of 4x, so 160 psi burst pressure.I ran a couple of plastics I have in my pressure program through internal and thenexternal pressure, & the maximum external pressure was 2/3rds the internal in both cases.This could mean that it would take 106 psi before the hose would equalize significantly.The diameter would maybe shrink a bit before collapsing.Cheers Alan

      From: Alec Smyth via Personal_Submersibles <personal_submersibles at psubs.org>
 To: Personal Submersibles General Discussion <personal_submersibles at psubs.org> 
 Sent: Wednesday, June 10, 2015 10:11 AM
 Subject: Re: [PSUBS-MAILIST] Dive report: Snoopy at Seneca

The stuff I'm using is really flexible, and has a wall thickness of only 1/16". I'm having trouble imagining that the seal could offer less resistance than this, it's very soft. See McMaster item #5552K25.
Best,
Alec
On Tue, Jun 9, 2015 at 5:29 PM, Alan James via Personal_Submersibles <personal_submersibles at psubs.org> wrote:

Does anyone (Sean) have the material specifications in theirpressure programs for the soft pvc that we would be using inour flexible compensation hoses?The nearest I had was nylon, & that had a crush depth of 8,000ftfor a 1 meter long tube, 10mm diameter & 2mm wall thickness.I was thinking of using oil filled light housings with the wiringrunning through flexible hose as compensation, but are having second thoughts.Alan
      From: Sean T. Stevenson via Personal_Submersibles <personal_submersibles at psubs.org>
 To: Personal Submersibles General Discussion <personal_submersibles at psubs.org> 
 Sent: Wednesday, June 10, 2015 6:11 AM
 Subject: Re: [PSUBS-MAILIST] Dive report: Snoopy at Seneca

I have always been a fan of oil compensation at higher than ambient pressure, for a variety of reasons. The only real downside is the environmental impact of potentially losing oil to the surrounding water in the event of a leak, but that impact can be mitigated with oil selection. Positive pressure allows you to compensate for volumetric changes in your compensated volumes due to the exterior pressure, as well as for thermal expansion of the oil, and if you have any leakage at all, you leak oil out, rather than water in, which can be an expensive lesson. Additionally, if you provide the bias with something like a spring loaded cylinder or elastomeric bladder, you can instrument its displacement for accurate monitoring of demanded compensation volume, and potentially detect leaks well in advance of when they actually become a problem.  Ambient-only compensation has the disadvantage of not compensating for boundary-layer viscosity effects on rotating shafts,! densitydifferences (gravity induced exchange and/or centripetally accelerated fluid) and other small but cumulative effects that can contribute to water ingress.  

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