[PSUBS-MAILIST] Dive report: Snoopy at Seneca
Sean T. Stevenson via Personal_Submersibles
personal_submersibles at psubs.org
Wed Jun 10 09:56:53 EDT 2015
I just caught up with this discussion. I'll write something about tube collapse when I get home this evening. As for a test can, I have previously used SCUBA cylinders that had failed their inspections due to problems in the thread or spot corrosion which I subsequently cut off and then just add a lid, but in this case, why not pipe the housing back to the cab and just throw a pressure transducer or gauge on that tube? What you're really interested in is the delta-P inside and out, correct? Off the cuff, I doubt you'll see anything. Those flexible hoses you are all using are not magically stiffening under pressure. Likely it's an air problem, or lack of expansion volume.
Sean
On June 10, 2015 6:20:32 AM MDT, Alec Smyth via Personal_Submersibles <personal_submersibles at psubs.org> wrote:
>What I'd really like to do is find some sort of pressure vessel I could
>use
>for running tests, actually measuring pressures inside the motor as the
>ambient pressure increases. I wonder what could be recycled for the
>purpose
>of creating a small test chamber?
>
>On Tue, Jun 9, 2015 at 11:24 PM, Alan James via Personal_Submersibles <
>personal_submersibles at psubs.org> wrote:
>
>> 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 expansion
>> characteristics 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 of
>> overpressure & 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 the
>> plastic 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 factors
>> included 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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