Re: [PSUBS-MAILIST] Caisson Gauge

[MerlinSub@t-online.de]

Old fighter jets from the 50-60ies have real robust pure mechanical one with a high range and are unexpensive. vbr Carsten. 


"James Frankland" <jamesf@guernseysubmarine.com> schrieb:
> Hi Jim,
> 
> Yes, altimeter sounds good.  i understand what you mean with the test.  Was
> going to do exactly that myself.  It was just the gauge I was being a dope
> about.  Its obvious now I've thought about it.
> 
> Had a quick look at altimeters.  Loads of different ones you can get.
> Cheapies, wrist watch ones, aviation, skydiving etc.  What make of
> altimeter are you using?  I do have a proper custom made caison gauge as
> well which came out of a diving re-compression chamber.  That might be ok
> but it will  need to be re-calibrated.
> 
> Anyway, plenty of other things to do first before I need to fit that.
> 
> Regards
> James
> 
> 
> 
> 
> On 27 March 2012 15:26, <JimToddPsub@aol.com> wrote:
> 
> > **
> > James,
> >
> > To clarify:  The reading of 5,000 ft. is what I've chosen for pre-dive
> > tests when the pilot is inside and the hatch has been latched.  When
> > testing the vessel for leaks in your shop *with no one inside *you want
> > to take it as far as you can.
> >
> > Even if you could pull a complete vacuum with a pump, the maximum
> > difference you can achieve is 1ATM or about 14.7 psi. which equates to a
> > depth of 33 feet or so in water.  In the shop test I'll go as far as the
> > pump and the altimeter can handle (maybe 100,000 feet above sea level).  If
> > it passes all that, the next step is dunking it in water to the appropriate
> > depth(s) or testing in a pressure chamber.
> >
> > Jim
> >
> >  In a message dated 3/27/2012 8:40:27 A.M. Central Daylight Time,
> > JimToddPsub@aol.com writes:
> >
> >  James,
> >
> > I'm planning to install an aircraft altimeter for the same purpose.  An
> > altimeter is simply a barometer with a wide range, so you could use that
> > instead.  It has the sealed air chamber (aneroid) which expands or
> > contracts in response to changes in external pressure.
> >
> > With the hatch closed and latched you can pump air out with an
> > external vacuum pump, turn the pump off, close the valve, take a reading on
> > the altimeter, wait a few minutes, then take another reading to see if any
> > air leaked back into the sub.  This can even be done with the sub
> > unoccupied as long as the altimeter is positioned where you can read it
> > through a viewport.
> >
> > In most cases you can use the adjustment knob to set the altimeter to 0
> > for the first reading.  I plan to run the vacuum pump until the gauge reads
> > 5,000 ft. altitude, shut the valve, and wait 5 minutes.  If the altimeter
> > reading drops to 3,000 feet for example, I know a seal is leaking
> > inwardly.  One caution:  If the sub is sitting in strong sunlight, you
> > could get some increase in internal air pressure just from heat build-up.
> >
> > This test is on my pre-dive checklist on every dive.  During a dive the
> > pressure reading should change very little if your scrubber and O2 inlet
> > are in balance.
> >
> > [image:
> > http://upload.wikimedia.org/wikipedia/commons/c/c3/Sens_alt_components.PNG]<http://upload.wikimedia.org/wikipedia/commons/c/c3/Sens_alt_components.PNG>
> >
> > Comments and criticisms are most welcome.
> >
> > Jim
> >
> >
> >  In a message dated 3/27/2012 7:36:00 A.M. Central Daylight Time,
> > jamesf@guernseysubmarine.com writes:
> >
> > Hi All,
> >
> > Mr Numpty here.
> >
> > I kind of know the answer to this already, but i thought someone may be
> > able to clarify my mistake.
> >
> > I was very pleased when i spotted just the sort of gauge i was after
> > mounted on the back of a sewage tanker.   A pressure gauge but one that
> > reads a negative pressure as well as a positive.   So it starts at 0 and
> > can go to -1 or +1 bar.  Idea was that it would go inside the cabin to
> > monitor internal pressure.  (I'd like it to be able to measure a negative
> > pressure as well as i intend to drop the internal pressure to test
> > for penetrator seal leaks).
> >
> >
> > http://www.tankerspares.co.uk/product/100mm_dia._30-0-30_Bottom_Mounted_Vacuum_Pressure_Gauge_30-0-301-4
> >
> > I was just thinking about mounting it up and ive suddenly realised that
> > its not going to work is it?  It must measure the port pressure relative to
> > the ambient pressure, which if i just mount it on a bulkhead will always be
> > the same no matter what the pressure actually is.
> >
> > I suppose i'd have to make a pressure proof box sealed at surface pressure
> > and pipe the port to the inside of the hull?   So its kind of like a
> > caisson gauge.
> >
> > Just thinking aloud really.
> >
> > James
> >
> >
> >
> 




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