Dear Professor Sajn:

Thank  you  for  taking  the time to explain the internals of the
regulators. The information in your mail is mostly appreciated. I
am  sure,  many  of  the  divers  in  the  fora will welcome your
explanations.

Best wishes,

----
aldo.solari@ho*.se* (fisheries biologist)
Home page, www.ccbb.ulpgc.es/fish-ecology/solaris
----

viktor.sajn@fs*.un*.si*

VS> Venturi  effect  is  depending on dynamical pressure of fluid
VS> flow   (meaning  with  density  of  inhaled  gas  and  square
VS> potential  of  velocity  -  breathing  intensity). So what is
VS> changing with different pressure in bottle and the same depth
VS> of  diving,  same rate of breathing (there are some other but
VS> not  so  important)?  Cracking  pressure  and IP - little but
VS> obviously you can notice it. Secret of regulator producers.

VS> The  one of the most important think in understanding of this
VS> anomalies  is that there are no just balanced and nonbalanced
VS> I  and  II  stages.  Most  of balanced I and II stages are in
VS> reality partially balanced. For example: most of all II Apeks
VS> stages (20,40,50) are balanced about 60% (as I remember of my
VS> last  time Apeks balance piston measurement). 40% of shutting
VS> force  is  caring  by  spring (adjustment of cracking force).
VS> This  meaning  when  you  inhale only pressure difference you
VS> have  to  overdo  is  the force of the spring (40%). Balanced
VS> part  of  force  (60%)is  released  almost  momentarily (with
VS> little time delay - important because of regulator fluttering
VS> possibility).  Now  Venturi (if it is adjusted) is activating
VS> because   of   dynamical  process  of  breathing  and  making
VS> uderpressure  on  membrane  and  by  this  it  correcting the
VS> cracking  pressure  (this 40% force of the spring). Again not
VS> to  much  because  it  is  possible  for  regulator to became
VS> unstable  -  fluttering.  (If you look at inhale test of some
VS> regulator,  just  look  at  the  inhale  graph  and find some
VS> oscillations  in pressure - this is acceptance design mistake
VS> -  for  me unacceptable example are tests of extreme balanced
VS> Poseidon   regulators).   With  depth  viscosity  of  gas  is
VS> increasing  dumping  also and fluttering usually stops. (this
VS> is  also typical experience of divers which use Poseidon). By
VS> my  opinion  (between  other reasons - and them are a lot) is
VS> much better to switch on He mictures to decrease viscosity of
VS> gas  and  regulator  will  work excellent also extremly deep.
VS> This is right way no extreeme balance unstable regulators.

VS> So  it  is  looking  that  it  is Venturi but in real that is
VS> because of partial balancing.

VS> Now you can imagine how many problems engineers have to solve
VS> to   make  regulator  working  properly  (right  diameter  of
VS> balanced  tube  -  proper  damping etc.). Sometimes they have
VS> luck  with  excellent design. Sometimes not. The real problem
VS> is  to  make  regulator  robust,  compact and time constant -
VS> reliable  and  on  the  other side low breathing effort. This
VS> Britt's  (Apeks)  are definitely succeed in compromise of all
VS> of  this  demands  and (by my opinion) are one of the best in
VS> world.

VS> So, you mentioned some remodeling of regulator?
VS> Fine.


VS> B.r.

VS> Viktor Sajn
VS> Laboratory of fluid mechanics and aerodynamics
VS> Faculty of Mechanical Engineering
VS> University of Ljubljana
VS> Slovenia

VS> (ps. be aware of extremely high balanced
VS> regulators - extreemly sensitive and danger)


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