[PSUBS-MAILIST] Lip seal

Thu May 21 09:10:34 EDT 2015

Alan, I agree with the second part of the statement and not the first.  What you describe in the first part would be correct if you had oil compensation and a stiff bladder.  For a soft bladder, the pressures both internal and external are balance regardless of depth and thermal expansion of the oil and as such, the seal does not lift off shaft and the water and oil don't mix.
Cliff

      From: Alan James via Personal_Submersibles <personal_submersibles at psubs.org>
 To: Personal Submersibles General Discussion <personal_submersibles at psubs.org> 
 Sent: Wednesday, May 20, 2015 9:32 PM
 Subject: Re: [PSUBS-MAILIST] Lip seal

Alec is kind of understanding me.On the microscopic level, at the very point of the V where it touches the propeller shaft,there must be a slight lifting with increased pressure from depth, due to pressure from water & oil from oposing sides pushing on the V of the seal & squeezing it up. This lifting will occur untill the oil & water actually meet.This may cause mixing of the two with the shafts rotational speed. However I am assuming that with this simple type of rotary shaft seal, the oil pressure (or water depending on the seal orientation) which would be in the cavity above the spring, would counteract this, leaving a consistant pressure on the shaft regardless of depth.Alan

   From: Alec Smyth via Personal_Submersibles <personal_submersibles at psubs.org>
 To: Personal Submersibles General Discussion <personal_submersibles at psubs.org> 
 Sent: Thursday, May 21, 2015 11:27 AM
 Subject: Re: [PSUBS-MAILIST] Lip seal

Alan, if the interior of the motor is in-compressible (as in liquid filled) there is no pressure differential. It's only the pressure differential that counts. There is no push from either side, and you could go to any pressure you like without the seal lifting.
Best,
Alec
On Wed, May 20, 2015 at 5:49 PM, Alan James via Personal_Submersibles <personal_submersibles at psubs.org> wrote:

While on the motor subject; a simple low pressure lip seal as below (substitute air side with water side)will be pressure compensated in a compensated motor! Is this correct?In oil compensation there will be oil pushing on the wedged shape of thelips mating surface, from one direction & water from the other. Eventuallythe pressure from both sides would lift the seal against it's spring pressure,but because of the recess above the spring that the oil gets in to, it  willmaintain the same pressure above ambient on the shaft throughout the depth changes.Alan

      From: Alan James via Personal_Submersibles <personal_submersibles at psubs.org>
 To: Personal Submersibles General Discussion <personal_submersibles at psubs.org> 
 Sent: Thursday, May 21, 2015 9:17 AM
 Subject: Re: [PSUBS-MAILIST] MK101 oil compensation tap

Cliff,how are you compensating for oil expansion due to heat with the KISS method.Are you just drilling holes in the housing & using tube?Alan

   From: Clifford Redus via Personal_Submersibles <personal_submersibles at psubs.org>
 To: Personal Submersibles General Discussion <personal_submersibles at psubs.org> 
 Sent: Thursday, May 21, 2015 8:43 AM
 Subject: Re: [PSUBS-MAILIST] MK101 oil compensation tap

Actually in the spirit of KISS, I am going to start out using oil pressure compensation.  If I run into any issues, I will look at using the air or this hybrid of oil and air with a regulator.  

Cliff Redus

On May 20, 2015, at 2:30 PM, Alan James via Personal_Submersibles <personal_submersibles at psubs.org> wrote:

Jon,the alternative is to follow Hugh's idea that Cliff is using & I am going to test out,& put a regulator in the system that is set it to around 4psi internal overpressure. This means you can fill with oil & not worry about getting everylast drop going in, or drilling the housing. You will also be able to run it air compensated. There is the safety feature that if you leak oil there is plenty of air to replace it.Cliff already has the parts sorted, just put your order in:)Alan
      From: Jon Wallace via Personal_Submersibles <personal_submersibles at psubs.org>
 To: Personal Submersibles General Discussion <personal_submersibles at psubs.org> 
 Sent: Thursday, May 21, 2015 5:47 AM
 Subject: Re: [PSUBS-MAILIST] MK101 oil compensation tap

How important is it to get every last air bubble out?  Surely a fraction 
of the total volume is not going to result in catastrophic failure of 
the motor housing, is it?

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