[PSUBS-MAILIST] Dive report: Snoopy at Seneca
Alan James via Personal_Submersibles
personal_submersibles at psubs.org
Tue Jun 9 21:37:32 EDT 2015
Alec,once you get past an inch or so in length at the diameter we are usingthe external pressure rating doesn't change.I think the same would apply to the internal rating; so they would be basing the 40 psi maximum pressure on an unlimited length of tube.Another factor may be the cold operating temperatures making it lessflexible.Alan
From: Private via Personal_Submersibles <personal_submersibles at psubs.org>
To: Personal Submersibles General Discussion <personal_submersibles at psubs.org>
Sent: Wednesday, June 10, 2015 12:45 PM
Subject: Re: [PSUBS-MAILIST] Dive report: Snoopy at Seneca
The hose is wound around the motor, so there are quasi-flattened parts I'm sure. But even if it were laid out straight, you would find the high length to diameter ratio would make it extremely susceptible to collapse via the general instability failure mode.
There are several types of PVC, and I wonder if the material properties you've got might be for the rigid type used in plumbing. This stuff is really soft and pliable.
Problem is, I still have no satisfactory explanation for why my motors or Hank's seal come up pressurized. I'm not convinced that these floppy hoses can withstand significant pressure, but I don't have a good alternative theory.
> On Jun 9, 2015, at 8:13 PM, hank pronk via Personal_Submersibles <personal_submersibles at psubs.org> wrote:
>
> Alan,
> My gut feeling is the hose will flatten quite easily as is because it has no support to keep it round. Just a feeling, can't argue with specs though.
> Hank
> --------------------------------------------
> On Tue, 6/9/15, Alan James via Personal_Submersibles <personal_submersibles at psubs.org> wrote:
>
> Subject: Re: [PSUBS-MAILIST] Dive report: Snoopy at Seneca
> To: "Personal Submersibles General Discussion" <personal_submersibles at psubs.org>
> Received: Tuesday, June 9, 2015, 7:54 PM
>
> Do
> you mean if it is crimped Hank?Or
> are you saying that just as is it will flatten
> easily?Alan
>
> From: hank pronk via
> Personal_Submersibles
> <personal_submersibles at psubs.org>
>
> To: Personal
> Submersibles General Discussion
> <personal_submersibles at psubs.org>
>
> Sent:
> Wednesday, June 10, 2015 11:27 AM
> Subject: Re:
> [PSUBS-MAILIST] Dive report: Snoopy at Seneca
>
>
> Alan,
> I think
> it will flatten under water right away because it is not
> round and has little strength to keep it round.
> Hank--------------------------------------------
> On Tue, 6/9/15, Alan James via
> Personal_Submersibles <personal_submersibles at psubs.org>
> wrote:
>
> Subject: Re:
> [PSUBS-MAILIST] Dive report: Snoopy at Seneca
> To: "Personal Submersibles General
> Discussion" <personal_submersibles at psubs.org>
> Received: Tuesday, June 9, 2015, 7:15 PM
>
> Hi
>
> Alec,that one
> is also showing 40psi.This is
> a
> Sean type problem.I guess
> it's a bit like snapping a match stick.
> Anyone can do
> it, but try breaking it
> bycrushing
> it from end to end. In this case
> you can squeeze the tube
> & bend it but
> try crushing
> it cross sectionally with
> even pressure all
> around.A
>
> solution may be to just squeeze up a section of the hose
> with a hose crimpso that a
>
> point of weakness is created for the water pressure to
> continue crushing thetube from
> there along it's length.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 10:55 AM
>
> Subject: Re:
> [PSUBS-MAILIST] Dive report:
> Snoopy at Seneca
>
>
> Wow. If
> there is no mistake that is really
> counter intuitive,
> because the hose feels
> super pliable in your fingers -
> almost like
> those yellowish rubber lab hoses if you know
> what I mean. The size I'm using is half
> the wall
> thickness of what you calculated
> with, if that makes a
> difference. It's
> 1/4" ID X 3/8" OD X
> 1/16"
> thickness.
> Alec
> On Tue,
> Jun 9, 2015 at 6:46 PM, Alan James via
> Personal_Submersibles
> <personal_submersibles at psubs.org>
> wrote:
>
>
> 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,!
> density
> differences
> (gravity induced exchange and/or centripetally
> accelerated fluid) and other small but
> cumulative effects
> that can contribute to
> water ingress.
>
>
>
>
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