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Re: [PSUBS-MAILIST] illustration is this what you mean sort of?? pressuriz...

Hi Jim,
I haven't done this before so I can only advise you from what I've heard & what seems logical.
There have been postings regarding oil compensating motors, where a clear plastic tube connects
between the top & bottom nipple. When any residual air in the motor is compressed at depth the tube
crushes & oil compensates for this diminished internal volume.
The oil bladder is an addition to this system & compensates for any loss of oil out the shaft seal, it also
pressurizes the inside of the motor above the sea water so if the seal leaks it leaks oil out, not water in.
There is no need for a pressure gauge permanently in the system.
Regards Alan
 
----- Original Message -----
Sent: Sunday, December 05, 2010 7:57 PM
Subject: Re: [PSUBS-MAILIST] illustration is this what you mean sort of?? pressuriz...

All,
 
I'm having difficulty understanding the need for the bladder, and it seems like an additional complication and an additional point of vulnerability along with the line.  How would this work:
 
1. Install a bleed valve at the uppermost point of the motor housing.
2. Install a fill valve at the bottom of the motor housing.
3. Attach a fill line (equipped with a pressure gauge) to the fill valve. Purge all air from the fill line prior to attaching it to the valve.
4.  With the bleed valve open, fill the motor from the bottom until oil discharges from the bleed valve.
5.  Turn the motor shaft by hand and vibrate the motor to release any trapped air bubbles.  Close the bleed valve and allow the motor to sit for a couple of days undisturbed.
6.  Open the bleed valve and add more oil to drive any residual bubbles out.  Close the bleed valve while pressure is still being applied to the fill.
7. Adjust the pressure from the oil pump to the desired pressure, then  close the fill valve.
8.  Release the pressure on the oil pump/fill line, then disconnect the fill line.
 
This seems logical to me, but I'd like to hear from the voice of experience.  Does 14 lb. seem like a reasonable differential pressure for set up?  I expect to start with new Minnkota motors, and I haven't addressed sticking with the factory seals vs retrofit seals.  My intended operational depth is 300 feet.
 
As always, comments  and criticisms are eagerly invited.
 
Thanks,
Jim
 
In a message dated 12/4/2010 10:07:34 P.M. Central Standard Time, alanjames@xtra.co.nz writes:
Hi Lawrie,
from what I can understand of the explanation on oil compensating a motor on the ROV site is this....
If you have a motor with half pie reasonable seals, you just fill it with a suitable low viscosity oil.
You have a drain nipple in to the bottom of the motor casing & a nipple for attachment of a hose
on the top of the casing. You attach a tube from the top nipple to a bellows or as they suggested
something like the bladder in a football. This is filled with oil & pressurized to about 15 psi so there
is always an external pressure of the motor oil over the internal pressure of the sea or lake water of
15 psi no matter what depth you are at. You can use the one bladder for all your motors.
The other option they mentioned was in the case where the motor might not be designed for underwater
applications & the seal not so good. In this case you can make an enclosure, put a suitable shaft seal
in the enclosure & do the same as the first option with the nipples tube & bladder but on the enclosure
not the motor. The motor inside would need to be filled with oil & have an opening in it. There shouldn't be
any air in these systems.
The idea of the seals back to back seems to be an additional option as a safe guard.
I bought a couple of trawling motors that I couldn't easily change the seals on so will be trying the oil
bladder method & if I'm going through too much oil then maybe air compensation or buying some better motors.
Regards Alan
 
----- Original Message -----
Sent: Sunday, December 05, 2010 2:53 PM
Subject: [PSUBS-MAILIST] illustration is this what you mean sort of?? pressurized oil compensation bladder for motors

Jim I created an illustration based on your concept as in outer oil housing and internal air housing for eletric motor.

I have shown the location for  a pressure sensor within the closed stem at the top of the outer housing and at the bottom a stem for the drain/fill/pressure up component not shown.

Is this sort of what you mean with regards to seals and using oil to indicate you water passing the seal and increasing the differential pressure between the two housings?  Lawrie

 

On Fri, 3 Dec 2010 22:48:55 -0500 (EST), JimToddPsub@aol.com wrote:

Great sites, Alan.  Thanks!
 
Lots of supplies/components when you click on the COMPANIES button.
 
Jim
 
In a message dated 12/3/2010 8:29:18 P.M. Central Standard Time, alanjames@xtra.co.nz writes:
Dan Fjellroth's website is a good resource for home builds.
Go to http://www.ROV.net then ROV FAQ and look for 'Build your own ROV'.