[PSUBS-MAILIST] Motor modification

Sat Dec 10 15:41:15 EST 2016

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 -  encased, 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 about two separate things?
>>> My question was based on wondering about that same clear tubing that
>>> wraps around the motor pods to allow for when the oil gets hot from use and
>>> expands.
>>> Taking any air out of the equation, I got the impression that you could
>>> completely fill a motor with dielectric oil (or any liquid for that matter)
>>> and then take it to any depth and since you basically can't compress a
>>> liquid, t! here would be no water ingress to the motor (except for the
>>> small space between the two prop shaft 0 rings.) So now when you add a
>>> slight internal increase in pressure from the oil being heated from use,
>>> people use the clear tubing that wraps around the outside of the motor
>>> (which is also 100% filled with the same oil) as a place for the oil to go
>>> to expand rather that spitting out the prop shaft 0 rings. Am I correct so
>>> far?
>>> So my question was, the clear hose wall must be flexible enough to allow
>>> for expansion before placing enough pressure on the prop shaft 0 ring to
>>> dislodge? And then if you don't get all the air out of the motor or clear
>>> hose or bladder, don't you have the water pressure trying to compress that
>>> bubble from not only the bladder or tube but past the shaft 0 ring as well?
>>>
>>> Rick
>>>
>>>
>>> On Mon, Dec 5, 2016 at 11:03 AM, Alan James via Personal_Submersibles <
>>> personal_submersibles at psubs.org> wrote:
>>>
>>> Some compensating thoughts.
>>> On James Cameron's sub they used IV drip bags. I am not sure what they
>>> were compensating.
>>> These come with various means of hose attachment.
>>>    With regard to the wrap around hose method; I did some calculations
>>> on a standard pvc hose, & surprisingly
>>> the colapse pressure was around 100psi. I am sure one of Nuytco's
>>> technicians told me they crimped the hose
>>> that was compensating their lights, to initiate the collapse of the hose
>>> for compensation.
>>>    The industry standard for thrusters seems to be around 4psi internal
>>> overpressure,
>>> but the compensators they use for this are relatively expensive. Hugh
>>> came up with
>>> the novel idea of using a releiving regulator set at 4psi (Parker
>>> PR364). Cliff is using this.
>>> This could be used for air or oil compensation.
>>>    The seals need oil for lubrication, & I have read that they can use
>>> about a teaspoon a day. Based
>>> on that I would have some sort of reservoir.
>>>    Depending on the motor it may be tricky to get all the air out. If
>>> you have a bearing in a bore
>>> followed by a seal, the air / oil would have to move through the bearing
>>> which may be a sealed type
>>>
>>>
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