Re: [PSUBS-MAILIST] Over Pressure Valve Options

["Jens Laland" <laland@artematrix.org>]

Hi Frank

I just like to say that what you just described is also the very principle
of the well-proven Papenberger Precision Depth Gauge used for decades by
german submarines to assist in maintaining a precise periscope depth.

These depth gauges are simple and easy to make - and works well from
surface and down to 15 or 20 meter water depth. The closed end of the
U-tube is terminated in a small reservoir of entrapped air. This extra
air-cushion helps to establish a better spacing between the individual
depth markings. The other end of the U-tube is open to the outside sea,
and therefore also to the free atmosphere at surface.

In the past, a similar U-tube manometer to what you described was also
often made by a boat's crew - ie. with one end hooked up to the battery
room. This was often a very crude, but highly accurate instrument that
helped people to monitor, and maintain a said underpressure within
hazardious gas zones (gas barrier). Maybe even an idea for the battery
pods (?)

Best regards,
Jens Laland

** The barometer we used was actually called a " manometer " and was
** connected
**  to air ducts. We had a high capacity blower connected to the ducts, and
** would  pump up the ducts to 5 or 6 inches of water column, and measure the
** leakage rate  which had to be 1/2 % or less.
** The tube was a clear vinyl at 3/8 inch dia. inside and was bent into a "U"
** shape about 24 inches long.
** The tube was attached to a rectangular plate with inch marks on both sides
** of the "U" tube.
** We used colored oil and it filled the bottom of the tube about 4  inches
** deep.
** Both ends of the tube were open, one being connected to the ducts that we
** were pumping up.
** As the pressure in the ducts rose, the oil would climb the open side of
** the
**  "U" giving us a reading of pressure in the ducts relative to the ambient
** room  pressure.
** Now this was a pretty accurate reading considering the simplicity of the
** device.
** For our purposes, we would set the tube in the sub, and plug one end with
** the hatch open, measuring atmospheric pressure as " zero" on the scale.
** The
** level of oil will be equal on both sides.
** With the hatch closed, and the sub submerged, If the pressure in the  sub
** rises, the air in the closed portion of the tube will compress slightly
** and
** the oil will rise due to the increased pressure on the still open end of
** the
**  tube. If the internal pressure drops below 1 atmosphere, the oil will
** rise
** on  the open side of the tube.
** Now, because the one end is closed, we won't get accurate readings of
** water
**  column, but we will get an indication that the pressure differential
** across the  open and closed ends has changed. Venting or adding air to the
** cabin
** will be  required to equalize the indicating oil level.
** Adding some air will be fairly easy, just crack the valve on a scuba  tank
** a little. Lowering the air pressure will be a little more difficult.
** Probably a small 12 volt air compressor connected to a snorkel pipe or a
** small
** container like an empty propane tank would be enough, or if the
** pressure/volume  wasn't that much, maybe just vent through the snorkel as
** you near the
** surface.
** Now I know this isn't very hi tech, but with a little testing, it should
** be
**  easy to grade the scale to reflect the changes in internal pressure by
** attaching  a gage to the sub hull, closing the hatch, and pumping the sub
** up
** while inside  and marking on the scale how much pressure relative to 1
** atmosphere is  reflected. That way we could establish where the safe depth
** to open
** the  snorkel is for any given over pressure reading.
** Because the tube is closed on one end, and the air bubble in that end must
** compress for the oil to rise, the first inch or so of rise will be easily
** detected, but as the pressure increases in the sub, the rise will be less
** evident, so the markings on the scale will become closer as the pressure
** differential increases. Again, using a gage viewed through the window,  we
** should be able to mark the scale at each portion of atmospheric change  up
** to
** what ever over pressure level we are anticipating might occur.
** Not very hi tech, but it appeals to my Scottish nature. Not necessarily
** cheap, but definitely thrifty! Frank D.
**
**
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