[PSUBS-MAILIST] over pressure valve

Fri Jun 19 17:28:43 EDT 2015

Alec,
At first I resisted the notion of thermal expansion, but I was thinking in terms of heat generated from motor use.  I didn't consider the temperature change from the sun on a black motor until the light went on :-)
I have changed my p trap ss tube to a larger hose so there is more air volume to work with.  I am ready to test that part.  Now I have to fix my bent up rudder :-(
Hank--------------------------------------------
On Fri, 6/19/15, Alec Smyth via Personal_Submersibles <personal_submersibles at psubs.org> wrote:

 Subject: Re: [PSUBS-MAILIST] over pressure valve
 To: "Personal Submersibles General Discussion" <personal_submersibles at psubs.org>
 Received: Friday, June 19, 2015, 5:03 PM

 Oh! Well I
 suppose it just depends on the volume the valve can handle.
 This is an interesting calculation, which I have not done
 but should. In general, these valves should handle pretty
 huge flow rates. But you're right, its basic to surface
 very slowly when there's any over-pressure - normally we
 dive with under-pressure. For a K-boat sized hatch, an
 over-pressure of 1/4 psi translates to a force of 95lbs
 trying to pull the dome out of the hatch ring. I know
 Snoopy's dome stays put at 1/4 psi, but I wouldn't
 take it any further than that just in case.   
 BTW, on the subject of calculations
 and changing topics back to the recent thruster compensation
 thread, you were right about the temperature change. The
 volume I had to compensate was a combination of thermal
 contraction and air bubble. The air bubble was of unknown
 size, but I ran the numbers on the thermal contraction alone
 and it is enough to cause the problem. The little hose only
 has a an internal volume of 10ml. The thermal contraction of
 the oil turned out to be 16ml - add to that the volume of
 the unknown bubble, and you can see the hose was inadequate
 even if it squashed to zero internal volume. I am now
 installing bellows bottles in place of the little hoses,
 with a capacity of 60ml. And a better filling method that
 should eliminate the bubble. You'd think I wasn't an
 engineer, assuming the effect of thermal contraction to be
 negligible. Its easy to focus the calculations on big items
 like hull strength or stability and make assumptions about
 the little stuff.
 Best,
 Alec
 On Fri, Jun 19, 2015 at
 4:19 PM, hank pronk via Personal_Submersibles <personal_submersibles at psubs.org>
 wrote:

 You have to be experienced to surface slowly and hover while
 the valve leaks out the
 air.--------------------------------------------

 On Fri, 6/19/15, Alec Smyth via
 Personal_Submersibles <personal_submersibles at psubs.org>
 wrote:

  Subject: Re: [PSUBS-MAILIST] over pressure valve

  To: "Personal Submersibles General Discussion"
 <personal_submersibles at psubs.org>

  Received: Friday, June 19, 2015, 4:16 PM

  I

  don't get the "in the hands" part... its

  completely automatic.

  On Fri, Jun 19, 2015 at

  4:09 PM, hank pronk via Personal_Submersibles <personal_submersibles at psubs.org>

  wrote:

  Agreed,

  In the hands of an experienced submarine operator an
 over

  pressure valve is safe, providing it is large enough. 
 I

  have not seen an example of a large enough OPV.  A
 simple

  valve in the hatch will do the same job, just need an

  umbrella :-)

  The noise of a compressor is a welcome sound if it
 means

  keeping the dome on the sub :-)

  Hank--------------------------------------------

  On Fri, 6/19/15, Carsten Standfuß" via

  Personal_Submersibles <personal_submersibles at psubs.org>

  wrote:

   Subject: Re: [PSUBS-MAILIST] over pressure valve

   To: "Personal Submersibles General
 Discussion"

  <personal_submersibles at psubs.org>

   Received: Friday, June 19, 2015, 2:47 PM

   But a overpressure vale works

   full auto. A compressor

   not.  

   A OPV needs

   no energy - but a compressor did.

   A OPV needs no room - but

   a compressor did.

   And a

   compressor is

   a noisy solution..

   vbr

   Carsten

   "hank

   pronk via Personal_Submersibles" <personal_submersibles at psubs.org>

   schrieb:

   > Personally I think an onboard

   compressor is a much safer option than an over
 pressure

   valve.  There are multiple safety benefits to an

  onboard

   compressor, over pressure being the biggy.  With a

   compressor you can get rid of the pressure without

  surfacing

   and trying to control a perfect ascent.  With the
 OPV

  you

   have to surface a bit and let air out and wait then

  surface

   more and wait and so on. You can't just surface
 and

  hope

   the valve keeps up with the demand. This is more

  important

   for subs with large domes.

   > The next

   benefit to a compressor is, if you lost all your air,

  you

   surface by dropping your weight.  In my case the
 weight

  is

   small and I would also drop the thruster and tail

  assembly.

   Still, not much sub out of the water.  With the

  compressor,

   I can open my vent valve in the hatch and use the

  compressor

   to fill the ballast tanks.

   > Hank

   >

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