User avatar
Chris
Master Diver
Posts: 470
Joined: Thu Mar 28, 2013 1:44 am
First Name: Chris
Location: Coos Bay Oregon
Contact: Website

Re: Phoenix/HPR/DBE's ready to go again!

Thu Jul 09, 2020 10:00 pm

I was thinking about asking what kind of antenna was screwed into your Phoenix, but now I know its a router so you dont have to physically screw in the coax.

User avatar
ScubaLawyer
Master Diver
Posts: 1577
Joined: Thu Apr 08, 2010 11:25 am
First Name: Mark
Location: Laguna Beach, CA

Re: Phoenix/HPR/DBE's ready to go again!

Fri Jul 10, 2020 12:46 am

Chris wrote:
Thu Jul 09, 2020 10:00 pm
I was thinking about asking what kind of antenna was screwed into your Phoenix, but now I know its a router so you dont have to physically screw in the coax.
Finally, someone understands me! 😎
"The diver who collects specimens of underwater life has fun and becomes a keen underwater observer. .. seek slow-moving or attached organisms such as corals, starfish, or shelled creatures." (Golden Guide to Scuba Diving, 1968) :D

MuffDiver
New Member
Posts: 5
Joined: Wed Oct 11, 2017 8:57 pm
First Name: Craig
Location: UK

Re: Phoenix/HPR/DBE's ready to go again!

Mon Jan 25, 2021 9:34 am

luis wrote:
Fri Jun 12, 2020 2:09 pm
Correct.

The "cracking effort" is the vacuum (or pressure differential) required to initiate the opening of the demand valve. At that point there is zero flow, therefore there is no venturi assistance or any other flow dynamic effect.

The water column differential between the top of the exhaust and the center of the demand valve diaphragm can be (and will be) what provides the pressure differential even if the diver is not inhaling. You can actually test this in a pool (or any comfortable calm body of water, even a big tub) with a DSV in the closed position and turn the regulator so that the exhaust is in a position higher than the demand valve diaphragm.


BTW, in single hose regulators they commonly call this issue: "case fault geometry". The "case fault geometry" describes the distance between the center of the demand valve diaphragm and the top of the exhaust valve when the diver is either up-side-down or in any position that places the exhaust valve edge at the highest possible (vertical) distance from the center of the demand valve diaphragm.

The significance of the "case fault geometry" is that it dictates the minimum cracking effort a single hose can be adjusted without getting into a free-flow condition in some diver position. Most single hose regulator cannot be adjusted to have a cracking effort to less than 1 inWC due to the "case fault geometry".

Scubapro went to a lot of trouble with the Pilot and later the Air-1 and the D series (D-300, D-350, D-400) regulators to have an exhaust valve concentric with the demand valve diaphragm (just like a double hose regulator with DBE or the Argonaut). Even when the diaphragm and exhaust are concentric you still have to deal the the radius of the valve and the distance to the top edge of the valve.


I hope this is clear and it makes sense.


Very helpful explanation Louis.

Would this issue also exist if a duckbill valve was used?

I.e. Could a PRAM with an HPR and a duckbill valve be tuned down to 0.3" without triggering the "case fault geometry" leak because the exhaust valve doesn't have a 'center" ?

User avatar
luis
VDH Moderator
Posts: 1665
Joined: Thu Jun 30, 2005 9:28 pm
First Name: Luis
Location: Maine

Re: Phoenix/HPR/DBE's ready to go again!

Mon Jan 25, 2021 7:00 pm

Yes, the water column physics still apply to a duckbill. As a matter of fact, many vintage duckbills were too short and the exhaust opening was often close to the horn, and not in the center of the can, in front to the center of the diaphragm.

You have to make sure the duckbill is long enough so that the opening is close to the center of the diaphragm.

If the duckbill exhaust opening is in front to the center of the diaphragm then all you have left is the width of the duckbill, which is again a bit over an inch wide. Therefore, from the center-line of the duckbill to the higher "edge-opening" you have a little over half an inch.

If you adjust the cracking effort to less than that pressure differential (again measured in "inches of water column"), the water pressure-differential will induce a free-flow when you are in a position that places that edge higher than the center of the diaphragm.
Luis

Buceador con escafandra autónoma clásica.

MuffDiver
New Member
Posts: 5
Joined: Wed Oct 11, 2017 8:57 pm
First Name: Craig
Location: UK

Re: Phoenix/HPR/DBE's ready to go again!

Tue Jan 26, 2021 5:35 am

Thanks Louis

A very helpful explanation which also implicitly answers the correct length of the duckbill.

Return to “Phoenix and Argonaut Specialty Area”

Who is online

Users browsing this forum: No registered users and 3 guests