[PSUBS-MAILIST] Motor modification

Mon Dec 12 14:01:40 EST 2016

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 others 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 contracting & sucking in water. Will re post their emails if
>I
>>>>>> can find them.
>>>>>> Regards Alan
>>>>>>
>>>>>>
>>>>>> ------------------------------
>>>>>> *From:* Rick Patton via Personal_Submersibles <
>>>>>> personal_submersibles at psubs.org>
>>>>>> *To:* Personal Submersibles General Discussion <
>>>>>> personal_submersibles at psubs.org>
>>>>>> *Sent:* Thursday, December 8, 2016 10:38 AM
>>>>>> *Subject:* Re: [PSUBS-MAILIST] Motor modification
>>>>>>
>>>>>> Alan,
>>>>>>
>>>>>> I am embarrassed to say that I am still not getting this concept.
>You
>>>>>> mentioned in your email about the clear hose that people wrap
>around there
>>>>>> Minn-Kota motors! and mention about collapse pressure and also
>mention
>>>>>> about lighting systems. Maybe we are talking abou
>>>>>>
>>>>>
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>>
>>
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