[PSUBS-MAILIST] Dive report: Snoopy at Seneca
Alan James via Personal_Submersibles
personal_submersibles at psubs.org
Tue Jun 9 23:24:39 EDT 2015
Hi Alec,>>> if we have 100% oil and no trapped air at all it should be the end of the story.
... No, the oil will heat up & expand & force it's way out the seals, then contract & suck in water.I am just repeating what Carsten & Emile have found by experience. You can look at the heat expansioncharacteristics of the oil you are using to get a worst case scenario of volume change.AS I have posted before, I like Hugh's idea of using a regulator that you can dial in a small amount ofoverpressure & compensate the motor with or without oil. It alows for expansion.After a bit of googling I came across a rubber tube of similar shore hardness (A65) & dimensions to theplastic tube you are using.It was rated -.95 to +16 bar. So that would mean it wouldn't crush at 13.9 psi, & with safety factorsincluded it could mean it wouldn't crush till 55 psi.I have advocated to people that they use this hose method to compensate lights :)The verdicts not out but I am very wary now.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 2:38 PM
Subject: Re: [PSUBS-MAILIST] Dive report: Snoopy at Seneca
All right, lets see what results that produces - I look forward to hearing. For my part, I'm going to concentrate on eliminating the leftover air because I agree, if we have 100% oil and no trapped air at all it should be the end of the story. I'm going to put NPT set screws in the nose cones as I think that will be the easiest way to fill without voids. I'm also trying to get new armatures, as the commutators have wear and I want to bring back their youth a bit.
Best,
Alec
On Tue, Jun 9, 2015 at 9:59 PM, hank pronk via Personal_Submersibles <personal_submersibles at psubs.org> wrote:
Alec,
There really is no other explanation than air in the motor. I can't see motor temperature causing it because the motor is in the most ideal environment (cold water) and full of oil. The air is compressing and water is entering past the seal due to shaft rotation and depth. It wouldn't matter if the hose did not collapse, because the motor is plumb full of oil in theory. My vertical thruster has no hose or bladder, it is just full of oil and it seems just fine, It only has one seal, so no little air space. It really does not take much air volume to create the problem, the inside seal will hold whatever small over pressure we create, until it fails of coarse and that is the visible oil we see causing dock side shame. :-(
One thing you could do if you want to keep the inner seal is to pack the void with grease.
I am changing Gamma's system this weekend to the open tube idea and am confident it will solve my leak.
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, 9:37 PM
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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