[PSUBS-MAILIST] Gauge for outside viewport?

Mon Sep 21 08:29:48 EDT 2015

Alec,Why wouldn't you just have the gauge inside the hull mounted directly to a shut off valve that is screwed into the hull, a simple tee in the line running down the hull.Hank 

     On Monday, September 21, 2015 6:20 AM, Alec Smyth via Personal_Submersibles <personal_submersibles at psubs.org> wrote:

 Hi James,
1) I have a bunch of oil filled gauges lying around, but if they are left in any position other than with the rubber caps at the top, they leak all over the place. The shelf they live on is covered with oil, so I'm just not confident they will keep the oil inside in the field.
2) Yes, SCUBA tank gauges have a tiny orifice in their hose fittings for just that purpose, to prevent a broken instrument from emptying your tank too quickly. That is good and I plan to use it on the sub as well. However, the problem still persists that SCUBA gauges can only be taken to under 500 feet. I came across tech diver accounts of gauge issues such as the plastic faces buckling and pinning the needle, or the whole enclosure imploding at about 400 feet. 

Thanks,
Alec  

On Mon, Sep 21, 2015 at 5:03 AM, James Frankland via Personal_Submersibles <personal_submersibles at psubs.org> wrote:

Hi Alec, I have a couple of thoughts.   1.  The gauges I have are chemical protected, so they have an oil filled diaphragm separating the inlet line from the gauge internals.  Then there is a small vent hole at the top of the gauge.  You could attach a rubber hose\bladder to this vent hole, top it up with glycerine or whatever the gauge is filled with and have a fully compensated valve with a bladder. 2.  How about using just a normal scuba gauge which will probably be perfectly fine.  But, just make a small adapter that screws onto the gauge and has only a tiny little orifice to allow the input air.  That way if the gauge did ever fail, it would only bleed out air slowly and you'd have time to blow tanks.  If you are using a scuba 1st stage and piping from the HP port (I assume your not and are plumbing straight into tanks) then the scuba HP already has this small hole for the same reason. Also, it would be easy enough to test a gauge.   Find somewhere deep enough and take a fishing rod and a packed lunch! Im fairly sure Emile has external gauges on his sub and its a 200m diver.  He could maybe advise? Just a thought.
Kind Regards
James  
On 21 September 2015 at 06:51, Brian Cox via Personal_Submersibles <personal_submersibles at psubs.org> wrote:

Hi Alec,    New sub ?  I must have missed that !    do you have any details?    BTW, I received that big gage !  It's huge !  I hope I can get it in through the hatch !   As it is designed for sea water I assume all I have to do is plumb it in, will salt water getting into the tubing cause any problems?   Brian

--- personal_submersibles at psubs.org wrote:

From: Alec Smyth via Personal_Submersibles <personal_submersibles at psubs.org>
To: Personal Submersibles General Discussion <personal_submersibles at psubs.org>
Subject: [PSUBS-MAILIST] Gauge for outside viewport?
Date: Sun, 20 Sep 2015 23:03:02 -0400

I have an interesting thing to think about and wondered if any of the PSUBS brain trust might have a suggestion.
One of the simplifications on my new sub is that all HP air lines are external, aside from the BIBS (which is normally shut off anyway). Thus, I'm looking for a 3,000-4,000 psi gauge to mount outside a viewport, like in the Pisces photo that I'll paste below. In case my paste doesn't come through, it is the one at the top of the following article: http://www.nytimes.com/2015/09/15/science/piloted-deep-sea-research-is-bottoming-out.html?_r=1
The first thing that came to mind was to use a SCUBA submersible pressure gauge, but the problem is these are normally 1 atm dry enclosures of limited depth rating. There is generally little information posted about how deep they'll go, but what I did find was mentioned 260 feet for the plastic ones and 490 feet for the brass variety. This is a 1,000 foot sub.
The second idea was to use oil filled gauges intended for above-water use. But these generally have considerable bubbles in the oil, are not very good at keeping the oil inside, and have other hardware not intended to live long in sea water.
Any suggestions would be most welcome!

Thanks,
Alec 

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