[PSUBS-MAILIST] Motor modification

Mon Dec 12 15:34:21 EST 2016

Thanks all, sorry to beat this to death but I tend to get over anal about
things as I have been a fabricator for 25 years so if there is something
missing on the plans or in question, I come to an all stop and get
clarification before proceeding. I blame it on breathing too much mixed gas
on deep dives😲

Rick

On Mon, Dec 12, 2016 at 10:07 AM, Brian Cox via Personal_Submersibles <
personal_submersibles at psubs.org> wrote:

> Rick,   I was thinking about using one of these:
>
> https://www.etrailer.com/Vehicle-Suspension/Firestone/F2580.html
>
> Brian
>
> --- personal_submersibles at psubs.org wrote:
>
> From: "Sean T. Stevenson via Personal_Submersibles" <
> personal_submersibles at psubs.org>
> To: Personal Submersibles General Discussion <personal_submersibles at psubs.
> org>
> Subject: Re: [PSUBS-MAILIST] Motor modification
> Date: Mon, 12 Dec 2016 12:01:40 -0700
>
> If you were going to go the bladder route - I didn't mean to imply a soft
> bladder just mounted by itself unprotected. If you use a bladder, put it in
> a housing of some sort. Just keep it open to sea pressure.
>
> Sean
>
>
> On December 12, 2016 11:25:33 AM MST, Rick Patton via
> Personal_Submersibles <personal_submersibles at psubs.org> wrote:
>
> Hi Sean,
>
> I would rather use the"hose wrapped around the motor" idea rather than a
> bladder basically as the hose is a much cleaner look and you don't have to
> figure out a way to secure the bladder from flapping in the breeze and you
> said the hose idea was fine in your #1 line but my concern is that though
> all the things you listed are true, I would think that the volume transfer
> after diving and warming up the oil in the motor would be (just throwing
> out numbers without data to support it) something like 5% inward and 95%
> outward from oil heating and armature rotation? so I would think based on
> that, that the hose could easily collapse enough " if pre crimped" to give
> in to the 5% inward flow but I can't see how the hose could expand enough
> to allow for the 95% outward flow without first spitting out the factory
> seals?  Sorry to beat this to death but I must be missing something. Would
> be nice to hear from other! s who have only used the hose method without a
> bladder to see if they have had any prop seal problems.
>
> Thanks
>
> Rick
>
> On Mon, Dec 12, 2016 at 6:18 AM, Sean T. Stevenson via
> Personal_Submersibles <personal_submersibles at psubs.org> wrote:
>
> The direction of oil flow is somewhat indeterminate. Heating of the motor,
> shaft, etc., will displace oil, while heating of the housing will consume
> oil. Cooling of the shaft will consume oil. Compression and deflection of
> the housing due to external pressure will displace oil on descent, and
> consume it on ascent. Contraction / expansion of any air bubbles in the
> system will do the opposite. Leakage past the seal! (s) will consume oil.
> Heating of the oil (operating viscous friction) will displace oil.
>
> Using a hose is fine, provided that:
>
> 1) it is soft and doesn't strongly resist external pressure collapse, and
> 2) as with any bladder, is only initially filled part way (pre collapsed),
> so that you have compensation capacity in both directions.
>
> Wall flex, as in diameter expansion when full, should never come into
> play. If you are hitting that limit (completely full tube), then you need
> to increase the tube volume until you don't.
>
> The more air you can get out of the system, the better, as you then don't
> need the compensation oil to compensate for the volume change as that air
> expands / contracts under pressure changes. Draw a vacuum before doing the
> oil fill if you can, but be mindful of not exceeding the capability of your
> seals. This is another reason why positive bias compensation pressure is
> helpful - if you have a high point in the line to vent from, you need only
> crack that open to vent any air until oil seeps from it.
>
> Sean
>
> On December 10, 2016 1:41:15 PM MST, Rick Patton via Personal_Submersibles
> <personal_submersibles at psubs.org> wrote:
>
> Sean,
>
> Good data to chew on. From what you and the others have said, it sounds
> like a partially filled airless bladder without hose would be the best way
> to go. It sounds like the major volume of oil that moves after diving would
> be in an outward direction, not inward and though the hose idea would allow
> for "some" inward flow, it just doesn't seem to have the wall flexing
> capability to accommodate the outward volume.?
> It's snowing as we speak here in Hawaii
>
> Rick
>
>
>
>
> On Sat, Dec 10, 2016 at 10:03 AM, Sean T. Stevenson via
> Personal_Submersibles <personal_submersibles at psubs.org> wrote:
>
> You can make the hose behave like a bladder by crushing / crimping it to
> initiate its collapse, and then only filling it to half of its undistorted
> volume, but then its rigidity or "memory" will make it act like it has bias
> pressure in the wrong direction - actually pulling the pressure down a bit
> from ambient, unless you specifically use a really soft tube. You can
> demonstrate this with a sample of hose, and you don't need an expensive
> vacuum pump to do it - just pull a vacuum on it with a large syringe, or
> cap the ends and take it diving. If it doesn't collapse easily with a
> relatively low external pressure applied, it isn't good for compensation.
> You want to avoid negative pressure in your compensated space, for obvious
> reasons. The tube idea works best with a tube which has no structural
> rigidity, in which case it's just acting like a bladder anyway. Which is
> why I prefer the bladder embodiment -  encas! ed, it is essentially a sm!
> all low pressure hydraulic accumulator, with the precharge side open to sea
> if compensating at ambient, or biased with gas pressure (or spring
> pressure) if adding some bias pressure.
>
> If you fill a rigid PVC tube completely (rigid in the sense that it
> resists collapse due to external pressure, even if it is "flexible"), the
> overpressure when the oil expands will either require the first seal to
> resist that pressure (which it is oriented the wrong way for in the default
> configuration), or will force oil past that seal into the inter seal space.
> If the housing subsequently contracts, oil is demanded from the
> compensation system, and if the tube can't deliver it, the oil pressure
> drops, loading the shaft seal if the inter seal pressure has been allowed
> to build up, which will prematurely wear out the seal.
>
> Ergo, best practice with regard to oil compensation is to provide
> compensation capacity in both directions, so that the compensation pressure
> is a true function of ambient pressure and neither bottoms out nor hits
> maximum expansion in operation.  You should also avoid having uncompensated
> void spaces between seals, as any leakage across a seal will change that
> pressure and you can't control it. This may be immaterial from a motor
> protection perspective, because compensation oil, if under biased pressure,
> will only leak away from the motor housing, but overpressure in the inter
> seal volume will eventually push oil past the second seal into the water,
> which is environmentally irresponsible.
>
> If you follow my earlier recommendation of using slightly biased pressure
> in the motor housing, and unbiased pressure between the seals
> (necessitating two separate compensation bladders), any oil leaking past
> the first seal (which will occur with increasing severity as that seal
> wears out) just transfers its volume to the unbiased compensation bladder.
> By monitoring the change post dive, you have an indication of seal
> condition. A loss of bias pressure (compensation failure) would indicate a
> serious leak which you could alarm on if you monitored that, as would
> monitoring the extremes of bladder displacement with limit switches.  If
> you want to be really fancy (Cliff?), you could encase the bladders and
> monitor the entire range of their travel with  displacement transducers to
> give you real-time seepage monitoring. Similarly, if the sum of both
> bladder volumes decreases, you know you are losing oil past the second seal
> to the water. A periodic analysis ! or observation of the oil in the
> unbiased bladder will tell you if you are exchanging oil for water at the
> second seal at constant volume.
>
> Sean
>
> On December 10, 2016 11:42:44 AM MST, Rick Patton via
> Personal_Submersibles <personal_submersibles at psubs.org> wrote:
>
> Hey Alan,
>
> Been tied up for a couple days since this post but thanks for the
> heat/expansion/volume data as it makes it much easier to comprehend. Based
> on what I see here, is it safe to assume that due to the amount of
> expansion of oil, just wrapping the motor several times with the clear PVC
> hose and connecting the other end to the second barbed fitting on the motor
> would not work due to the fact that the hose would not expand enough to
> allow for the volume of expanded oil where as a bladder half filled would
> work better?
> Also would like to hear from the others out there who have used only the
> clear hose to see if they have had any issues with leakage?
>
> Thanks all
> Rick
>
> On Wed, Dec 7, 2016 at 1:42 PM, Alan James via Personal_Submersibles <
> personal_submersibles at psubs.org> wrote:
>
> Rick,
> Sean's beat me to it, but I'll add that you can usually look up
> your compensating oil's coefficient of thermal expansion, &
> calculate how much it will be. Engine oil is abou! t .0007. That
> would mean that if you had a liter of oil (1000cc) & the temperature
> went up by 50 degrees C, then the oil would expand another 35cc.
> Not a lot given  that you would not require a lot of oil in the thruster.
> Getting the air out could be a bigger problem & it would expand more.
> In a declassified military document on compensating I read , it talks
> about & demonstrates how to pull a vacuum on a thruster to get all
> the air out.
> Another issue that I mentioned earlier is that all seals leak oil to
> lubricate themselves, so having a reservoir makes sense.
> What I am doing is enclosing my motor wiring in a hose & filling
> the motor & hose with oil. In to this I will have a T to a relieving
> regulator
> (PR 364) that will pressurize the system with air at 4psi above ambient.
> Carsten & Emile had all sorts of problems about ! oil expanding & leaking
> then c
>
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