[PSUBS-MAILIST] Mechanical Depth Gauges

Douglas Suhr via Personal_Submersibles personal_submersibles at psubs.org
Tue Jul 31 13:31:43 EDT 2018


Nothing complicated to you Alec, but remember that sometimes I have
trouble dressing myself in the morning! Thankfully, with the graphic
you shared I won't have to worry about spacing, etc. No chance you
recall how to remove the needle(?). It looks like a friction fit, but
I don't want to force it off either (might bend it).

On 7/31/18, Alec Smyth via Personal_Submersibles
<personal_submersibles at psubs.org> wrote:
> Hi Doug,
>
> Yes, it was in psi. All I did was calculate how many psi corresponded to
> the max depth I wanted to show (300 fsw), note where that fell on the face
> of the instrument, and subdivide the included angle into equal segments
> when I drew the new face plate. Nothing complicated.
>
>
> Best,
> Alec
>
> On Tue, Jul 31, 2018 at 11:21 AM, Douglas Suhr via Personal_Submersibles <
> personal_submersibles at psubs.org> wrote:
>
>> Alan - Thanks for the info on these computer programs... perhaps it is
>> something that I will look into. You're right that between all of us
>> psubbers (and especially Jon / Cliff) I could probably figure it out.
>>
>> Alec - thanks for the gauge graphic! Here's another question for you:
>> When you bought this gauge, I'm guessing that it was intended to read
>> PSI? When you designed that label, how did you go about getting the
>> spacing of the feet numbers correct? ~ Doug
>>
>> On 7/30/18, Alec Smyth via Personal_Submersibles
>> <personal_submersibles at psubs.org> wrote:
>> > Hi Doug! I looked on my laptop and sure enough found a simple 2D CAD
>> > file
>> > called "Depth gauge faceplate." So here you go, I'll paste a screen
>> > shot
>> > below so you can print it. It's black and white, and the red was I
>> > think
>> > just done with a marker over the hatch pattern. Looking at this, the
>> "250"
>> > is not quite straight, but when printed at the scale of the instrument
>> > I
>> > don't recall noticing it. So... just try printing this a few times
>> > until
>> > you get the scale right, then cut out with scissors and then paste
>> > right
>> > onto the instrument. That's all there is to it.
>> >
>> > Concerning the question about whether the instrument sees water, here's
>> an
>> > explanation for everyone else. The pressure gauge is in the CT, high in
>> the
>> > boat, but the line that feeds it pressure comes into the hull at close
>> > to
>> > the lowest point. It is open to the sea, and as you dive the air in the
>> > line will of course compress. It will not, however, ever compress
>> > enough
>> > that the sea water actually reaches the instrument. The gauge measures
>> the
>> > difference between inlet pressure and ambient, so the instrument case
>> > is
>> > not sealed or it would establish a reference pressure. There is an
>> opening
>> > in the case in order to equalize pressure, and as I recall a little
>> filter
>> > element intended to keep dust out but let air through. It will let in
>> cabin
>> > humidity too, which in places like the keys probably means you'll print
>> > a
>> > new paper face-plate from time to time.
>> >
>> > Best,
>> > Alec
>> >
>> >
>> >
>> >
>> >
>> >
>> > On Mon, Jul 30, 2018 at 2:36 PM, Douglas Suhr via Personal_Submersibles
>> > <
>> > personal_submersibles at psubs.org> wrote:
>> >
>> >> Ah, I think you're right Jon... because the gauge plate would not be
>> >> pressured anyway, huh. Never thought of that.
>> >>
>> >> No there was no gasket or anything, so I guess any moisture in the
>> >> viewing portion of the gauge would just come from moisture inside the
>> >> hull of the sub.
>> >>
>> >> And thank you for the pressures... not a huge difference but I suppose
>> >> at deep depths it could work out to be somewhat of an error.
>> >>
>> >> I wonder how Alec printed such a nice looking label(?). ~ Doug
>> >>
>> >> On 7/30/18, Jon Wallace via Personal_Submersibles
>> >> <personal_submersibles at psubs.org> wrote:
>> >> > Fresh water: .433psi per footSalt water: .445 psi per foot
>> >> > If there was no gasket sealing the acrylic/glass cover and bezel
>> >> > then
>> >> it's
>> >> > likely condensation caused the wrinkling of the label.
>> >> > Jon
>> >> >
>> >> >       From: Douglas Suhr via Personal_Submersibles
>> >> > <personal_submersibles at psubs.org>
>> >> >  To: Personal Submersibles General Discussion
>> >> > <personal_submersibles at psubs.org>
>> >> >  Sent: Monday, July 30, 2018 1:16 PM
>> >> >  Subject: [PSUBS-MAILIST] Mechanical Depth Gauges
>> >> >
>> >> > All, as you may've been aware, in late 2015 I purchased Snoopy (a
>> >> > K-250) from Alec Smyth. Regrettably I have been quite neglectful of
>> >> > performing much upkeep on the sub, save for keeping the batteries
>> >> > topped off. My schedule is finally allowing me to spend some real
>> >> > time
>> >> > working on the sub and getting to know the specifics of each system.
>> >> >
>> >> > As you can imagine, I've been bugging Alec with a question here and
>> >> > there, but thought with this topic I should start a discussion here
>> >> > on
>> >> > the list for the benefit of anyone else who might have questions /
>> >> > curiosities about mechanical depth gauges.
>> >> >
>> >> > Snoopy's depth gauge is nice and large (about 5" in diameter) so
>> >> > it's
>> >> > easy to read. Alec created a nice label for the gauge face which
>> >> > reads
>> >> > from 0 to 300 (in feet) with the last fifty feet being marked in red
>> >> > to indicate 'too deep.'
>> >> >
>> >> > Problem is, when I looked at the depth gauge the other day, I
>> >> > noticed
>> >> > that the transparent cover plate on the gauge looked to be quite
>> >> > opaque (to the point where I couldn't quite read the numbers or
>> >> > count
>> >> > the hash marks). I assumed that there was some moisture trapped in
>> >> > the
>> >> > gauge, causing the obscuration. I decided to remove the gauge from
>> >> > the
>> >> > sub and open it up to let it dry out.
>> >> >
>> >> > After removing the gauge from the sub, I unscrewed three small
>> >> > screws
>> >> > around the bezel and popped off the transparent cover plate. It was
>> >> > only then that I realized the opaqueness was not caused by moisture
>> >> > but a distortion in the clear plastic. The distortion (like super
>> >> > fine
>> >> > scratches) appears to be on the outside of the cover, as though it
>> >> > was
>> >> > cleaned by something that started to melt the plastic or was left
>> >> > out
>> >> > in the sun too long. I don't think either of these explanations make
>> >> > sense, but I'm puzzled as to what might have caused it. I might try
>> >> > to
>> >> > buff / polish the plastic, or perhaps just replace it with glass.
>> >> >
>> >> > I think it's a good idea to stick a dive computer in viewing range
>> >> > of
>> >> > a viewport for a depth reading, but I like the idea of having a
>> >> > mechanical gauge in the sub as well. A couple of questions that come
>> >> > to mind: what is the pressure variation between salt water and fresh
>> >> > water? Also, although I didn't find moisture in the gauge, The label
>> >> > on the face is wrinkled a bit as though it has seen moisture.
>> >> > Although
>> >> > water should never actually reach the gauge, I can see how moisture
>> >> > from the inlet tube could find its way up into the gauge body.
>> >> > Should
>> >> > I be concerned about drying it out somehow after a dive (especially
>> >> > in
>> >> > salt water)? If so, how should I go about it? ~ Doug S.
>> >> > _______________________________________________
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>> >> >
>> >> >
>> >> >
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