[PSUBS-MAILIST] Air compensation

Tue Jul 22 21:29:57 EDT 2014

Cliff,
I bought 2 Festo polymer regulators LR-1/4-DB-7-MINI. They are cheap at NZ $50- list price.
I couldn't find a suitable replacement stainless spring for them so put them on the shelf for a while.
I was looking to replace the winding mechanism that sets the spring pressure, with stainless, but also couldn't find
anything suitable. In hindsight this mechanism could be replaced by packing with a number of plastic washers to
get the right spring tension. These units are piston type, so not as sensitive as Hugh's find, which are diaphragm type.
This difference could be important as the backpressure releif pressure may be too high on the Festo. 
That said Karl Stanley has been letting his overpressure build up till it vents through his propeller shaft seals.
Still a bit of research & experimentation to be done with this one.
Cheers Alan

________________________________
 From: Hugh Fulton via Personal_Submersibles <personal_submersibles at psubs.org>
To: 'Personal Submersibles General Discussion' <personal_submersibles at psubs.org> 
Sent: Wednesday, July 23, 2014 8:29 AM
Subject: Re: [PSUBS-MAILIST] Minn Kota 101 - thread spec

Hi Cliff,  

These are NZ dollars.
List is $228.00. 
My buy is $114.00 per unit. (About $100 USD) I get them direct from Parker.

I am using the regs on the Mercruiser drive bellows and the pneumatic actuator Cylinders, spring return side.
I am setting at 5 psi.  

Hugh

From:Personal_Submersibles [mailto:personal_submersibles-bounces at psubs.org] On Behalf Of Cliff Redus via Personal_Submersibles
Sent: Wednesday, 23 July 2014 2:00 a.m.
To: Personal Submersibles General Discussion
Subject: Re: [PSUBS-MAILIST] Minn Kota 101 - thread spec

 Hugh this PRV with the built in pressure relief option looks like it would do the job.  On the Q-sub, what equipment are you using this pressure reducing regulator on for air pressure compensation?  I found these at Mscdirect for $245.54 for model PR364-02BSS.  

Cliff

From:Hugh Fulton via Personal_Submersibles <personal_submersibles at psubs.org>
To: 'Personal Submersibles General Discussion' <personal_submersibles at psubs.org> 
Sent: Tuesday, July 22, 2014 12:10 AM
Subject: Re: [PSUBS-MAILIST] Minn Kota 101 - thread spec

From:Personal_Submersibles [mailto:personal_submersibles-bounces at psubs.org] On Behalf Of Cliff Redus via Personal_Submersibles
Sent: Tuesday, 22 July 2014 12:27 p.m.
To: Personal Submersibles General Discussion
Subject: Re: [PSUBS-MAILIST] Minn Kota 101 - thread spec

The Titan first stage is a Balanced Diaphragm Design.  I am not sure if it will have the hysteresis effect you discuss with your experience with using a balanced piston type 1st first stage.  Thanks for mentioning this hysteresis.  I will do some bench test to check.  As you did on your ambient boat, I can always add a 2nd stage if I need better ambient air pressure control for pressure compensation.

Hugh, can you post the model and manufacturer of the pressure reducing regulator Alan is refereeing to?

Rather than having a dedicated tank for compensation air, to keep it simple I was just going to run the air compensation regulator off the main ballast air supply.  I already have a pressure sensor on the HP air pressure and low pressure alarms.  I also have tank pressure sensor  interlocked through the PLC with my flood ballast controls so that the pilot can not dive the boat if the air pressure in the tanks is less than 50% of max.  

But in the spirit of KISS, it is hard to argue with the simplicity of oil compensation with a flexible hose for these MD-101's.

Cliff

Cliff Redus
Redus Engineering
USA mobile:  830-931-1280
cliffordredus at sbcglobal.com 

From:Alan James via Personal_Submersibles <personal_submersibles at psubs.org>
To: Personal Submersibles General Discussion <personal_submersibles at psubs.org> 
Sent: Monday, July 21, 2014 5:46 PM
Subject: Re: [PSUBS-MAILIST] Minn Kota 101 - thread spec

Cliff,
I am not sure of the workings of the Titan, but I did some experimentation with a balanced piston type 1st stage.
You just open it up & take the spring out & you have ambient pressure. It wasn't as accurate as a 2nd stage for
maintaining ambience. I think it needed to go a foot or so under water to open up & then from memory there was more
overpressure than I wanted. On my ambient sub I have a couple of $90- 2nd stage octopus regulators mounted lower than the motors.
Vance said he was involved in taking Karls motors apart & they had a bit of moisture damage. 
However it's not known if this was from sea water getting in through the seals or from poor filter systems for filling 
the scuba tanks. He was taking these motors down to 2000 ft, so a lot of air is going in to the motors & any moisture 
in the air would probably drop out of suspension & stay in the motor. I think they had been running for a couple of years
& probably been sitting in water all the time.
   Hugh found a good stainless regulator reasonably priced. You will have to ask him for the details if interested.
You need to mount these pressure regulators upside down, as the hole for exhaust & ambient equalization is in the 
handle & mounting it this way will stop water getting in the valve area when it opens.
I wouldn't want to put all my eggs in one basket by trying to compensate all motors off the one system. If you lost all propulsion
& were being washed on to rocks it could be nasty.
Another thought is to put a low air pressure alarm on your plc for the monitoring of your air tanks, in case there is a leak & you deplete your 
ballast / compensating air, or in case you forget to turn your air tanks on at the bottle. (that would be bad)
Cheers Alan

From:Cliff Redus via Personal_Submersibles <personal_submersibles at psubs.org>
To: Personal Submersibles General Discussion <personal_submersibles at psubs.org> 
Sent: Tuesday, July 22, 2014 9:31 AM
Subject: Re: [PSUBS-MAILIST] Minn Kota 101 - thread spec

I have a spare Aqualung Titan first stage regulator that I can use to pressure compensate all four MK-101's so I would just need one small pressure relief valve and some SS tubing and Swagelok fittings.  The key to me is can the regulator set screw be backed out to the point of getting less than one psi over ambient.  I need to do some bench testing.  I like using scuba first state as is built for seawater.

There is a lot of ways to skin this cat.

Get some sleep.

Cliff

From:Alan via Personal_Submersibles <personal_submersibles at psubs.org>
To: Personal Submersibles General Discussion <personal_submersibles at psubs.org> 
Sent: Monday, July 21, 2014 2:59 PM
Subject: Re: [PSUBS-MAILIST] Minn Kota 101 - thread spec

Cliff,
No worries, Hugh will have 2 subs to rescue me with by the time
mine is finished. The beauty of Hugh's regulator method is it
exhausts the overpressure, & a hole in the handle enables the system
to maintain your set pressure above ambient. I bought a cheap fibre reinforced plastic
regulator with the back pressure exhaust function for compensating,
but there were a few springs & bits that needed replacing with stainless.
Another option may be to oil compensate & use 1 regulator to pressurise
all motors. Just design it so that if the regulator or air lines failed, the compensating
oil wouldn't float out & would keep the motor pressurised at ambient.
Cheers Alan
Sent from my iPad

On 22/07/2014, at 5:40 am, Cliff Redus via Personal_Submersibles <personal_submersibles at psubs.org> wrote:
Alan  I am glad your not advocating abandoning pressure compensation on your thrusters.  I would sure hate to have to fly to New Zealand and rescue your skinny ass off the bottom near White Island!
> 
>If I use air to pressure compensate by MK-101's,  I would use a variation of what Karl Stanley and Hugh Fulton are doing, i.e., use a scuba first stage regulator with the spring fully back out to get as close to ambient water pressure as I can  but rather than letting air leak out the lip seal on ascent use an OTS ball style pressure relief valve with a 0.5 psi cracking pressure.    Would need to play around with the amount of cracking pressure and the screw setting on the first stage to make sure it vents through the valve and not the lip seal.
> 
>Agree, it would be good to get the Europeans experience on oil vs air pressure compensation of trolling motors.
> 
>Cliff
> 
> 
>From:Alan via Personal_Submersibles <personal_submersibles at psubs.org>
>To: Personal Submersibles General Discussion <personal_submersibles at psubs.org> 
>Sent: Monday, July 21, 2014 11:08 AM
>Subject: Re: [PSUBS-MAILIST] Minn Kota 101 - thread spec
> 
>Hi Cliff & all,
>thanks for the expansion calculations Cliff. 
>I wasn't advocating using the 101s without compensation.
>Just saying that they may not fail with the tube method because 3 out of 4
>would operate down to 100ft with no compensation anyway.
>Karl Stanley uses a first stage divers regulator with the spring removed to
>give ambient air pressure to his motors; & just lets the over pressure on ascent
>bubble out of the seals.
>   Hugh had the idea of using a pressure regulator that has back pressure relief.
>you just dial in an over-pressure of air to the motors. The stainless ones cost a couple of hundred each & you would probably need one on each motor + valves for each
>to stem air flow if there was a failure.
>   Will try & dig up the negative comments on oil compensation made by the Europeans. 
>(when I wake up) Have them somewhere.
>Regards Alan
>
>Sent from my iPad
>
>On 22/07/2014, at 2:22 am, Cliff Redus via Personal_Submersibles <personal_submersibles at psubs.org> wrote:
> James, a couple of points.  First, to me the fewer the leak paths the better so I would not install the added plug.  The issue is how to get traped air out of the Md-101 when using oil compensation.   I like Alec and Hanks ideas for removing trapped air due to nipple protruding into body.  The other point is the wrap around tube volume can compensate for the small amount of air that remains trapped.  To deal with thermal expansion of the oil, first of all you are dealing with a small volume to start with so the tube/reservoir does not have to be all that large.  If you do a quick back of the envelope calc on the required volume to compensate for only thermal expansion of the oil you about need 3 US teaspoons for a MK 101 ( Assume oil has a thermal expansion coefficient of 0.00056 1/F and that there is one US pint of oil in the body of the 101 and that the temperature swing is 70F to 130F.  Delta volume is 0.125 gal * 0.00056 1/F * 60F =
 0.0042 gal*128 OZ/gal *6 US TSP/OZ = 3.2 teaspoons).  
>>To me the design pressure inside the ME 101 should be ambient pressure as they have lip seals on shafts.  Lip seals are design to take external pressure.  They re not designed to take internal pressure.  So a simple wrap around tube for oil compensation with say a volume of 5 US teaspoons should work just fine as this would allow for thermal expansion of the oil and a small volume of trapped air and because the tube is flexible, the pressure inside the 101 is ambient which makes the lip seal happy.  As to Alan's suggestion on omitting all pressure compensation and only relaying on the lip seal without any pressure compensation, I am not wild about this idea unless the boat is only designed for shallow water.  MK designers when they speced the lip seals for MK were designing shallow submergence of a trolling motor with a factor of safety.  So as you get deeper and deeper, you are starting to expose these lips seals to a significant differential
 pressure which causes them to overheat and fail at some point.  Is this 10ft or 50 ft or 100 ft.  Don't know but to me this exposes the boat to some risk particularly if use the 101's for depth stability rather than a VBT and dive the boat negatively buoyant, i.e., vertical thruster fails, boat starts to descend and pilot is forced into dropping ballast.  
>> 
>>To me a bigger question on air vs oil compensation is how much power are you giving up with oil compensation due to viscosity difference between oil and air.  
>> 
>>As both Alec and Vance point out, there has been a lot of bottom time on MD-101s with oil compensation without a lot documented failures.  
>> 
>>I have not decided in my own mind which compensation method I will use on my MD-101's for future boats.  
>> 
>>Cliff
>> 
>> 
>>From:James Frankland via Personal_Submersibles <personal_submersibles at psubs.org>
>>To: Personal Submersibles General Discussion <personal_submersibles at psubs.org> 
>>Sent: Monday, July 21, 2014 4:17 AM
>>Subject: Re: [PSUBS-MAILIST] Minn Kota 101 - thread spec
>> 
>>Hi Cliff,,
>>Others may disagree with this, but ive got a suggestion.  If your oil compensating the motors and are going to add the wrap around tube\bladder as per Alecs Snoopy, I would suggest, adding a vent hole somewhere near the aft bearing.  With my setup, ive put the tube going around the motor and its all ok.  But, I just cannot get the last dregs of air out.  No matter what I do.  I suspect that its because the pipe nipple protrudes a mm or so into the casing and so will not allow the last bit of air out.  It really irritates me and I worry that the motor is not properly compensated.  So, I am going to make a modification to the motor like this pic.  I think this will work, the suspect bit is mating the plug against the slightly domed motor case.  I think a large rubber washer should seal it.   The i should be able to rotate the motor and remove the last dregs of air.  What do you think?
>>Thanks
>>James
>>
>><motor.jpg>
>> 
>> 
>>On 19 July 2014 01:38, Clifford Redus via Personal_Submersibles <personal_submersibles at psubs.org> wrote:
>>Thanks
>>Cliff Redus
>>
>>On Jul 18, 2014, at 7:26 PM, Alec Smyth via Personal_Submersibles <personal_submersibles at psubs.org> wrote:
>>Hi Cliff,
>>> 
>>>It is a parallel thread, 1 1/8" - 18.
>>> 
>>>Best,
>>> 
>>>Alec
>>> 
>>>On Fri, Jul 18, 2014 at 8:04 PM, Cliff Redus via Personal_Submersibles <personal_submersibles at psubs.org> wrote:
>>> Does anyone have any documentation on the Minn Kota 101 main support female thread spec?  It does not look like a tapered pipe thread and the threads per inch look to great. I put a digital caliper on this at it read 1.064-1.07 inches for the minor diameter.  I measured the threads and it is 18 threads per inch.    I looked in the machine handbook and the closest that comes is a 1-1/8  UNEF (Extra fine thread series).  The major and minor diameters for a 1-1/8" UNEF are 1.1250" and 1.0649"  respectively.
>>> 
>>>Can anyone confirm this?
>>> 
>>>Cliff
>>>
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