DAAquamaster
Skin Diver
Posts: 25
Joined: Mon Aug 08, 2016 9:14 pm
First Name: Larry
Location: Winterville NC

Interesting silicone duck bill issue.

Mon Aug 08, 2016 11:07 pm

I recently converted another DA to PRAM configuration, this one in DIN, and rather than using the Duck Bill Eliminator I tried a silicone duck bill on it, in part due to the reports of lower exhalation effort and in part due to the round label can where the DBE can cause some interference with the diaphragm.

It worked great and the exhalation resistance was less than with a duck bill eliminator which in turn is a little better than the older rubber duck bill.

However, this weekend I took my new VDH back plate for a spin, to see how it compared to my Freedom plate, and after a short swim I decided I needed to re-adjust the harness as the can was riding up a bit too high and I needed to shorten the crotch strap and lengthen the shoulder straps. In the process I turned off the tank valve to prevent losing gas while adjusting the harness in the water, and inserted a mouthpiece plug. Then I apparently stretched the exhaust hose.

The end result was that the low pressure in the hose caused by the stretched hose with the mouthpiece blocked and no gas in the regulator, sucked the silicone duckbill back inside the hose. Of course, as soon as I tried to exhale, the positive pressure in the hose forced the duck bill closed, as it was now inside the hose, not outside it, and I could not exhale at all.

Fixing it required separating the cans and then exhaling through it to force 1/4" or so of the duckbill out so I could pull it the rest of the way out. It's wasn't exactly an in-water fix.

I played with it a bit to replicate the failure and I found that with the mouthpiece and inhalation side both blocked a moderate hose exhaust hose stretch would suck it back in the exhaust hose every time.

Now...a disclaimer here is that I am also diving EDPM hoses with 1" ends to accommodate Hope-Paige mouthpieces (I'm really looking forward to the new DSV). One thing I love about these hoses is that they are much more compact - very much like the hoses on my KISS Sidekick. They are much more streamlined in the water, and much quieter than the standard silicone rubber USD pattern hoses. But they have a much greater accordion effect with much more potential volume change that probably exacerbates the duckbill issue.

I mention this as with the new DSVs showing up in the near future, it is possible that folks might start having similar issues, if the hoses get stretched while the gas is off and the mouthpiece is blocked. If that's the case, a duckbill eliminator mod is a good idea to go along with the new DSV.

For that matter the same thing is possible with a mouthpiece plug - and it may be a known issue that I have just never encountered or hear dog before.

Or it could just be a perfect storm of a very flexible silicone duck bill, very stretchy EPDM hoses and an efficient mouthpiece plug.

Anyone have a similar experience?

Larry

User avatar
luis
VDH Moderator
Posts: 1609
Joined: Thu Jun 30, 2005 9:28 pm
First Name: Luis
Location: Maine

Re: Interesting silicone duck bill issue.

Tue Aug 09, 2016 7:26 am

DAAquamaster wrote:
If that's the case, a duckbill eliminator mod is a good idea to go along with the new DSV.

Larry
Even better... an Argonaut is a better choice to go with the DSV. :wink:
If you really want extremely low exhaust flow resistance, try an Argonaut.


Yes, about duckbill inversions. It has only happened to me once, but it can happen. It will probably never happen to me again... I don't really dive regulators with duckbill anymore.

You can use some silicone bonding and glue a spot of the duckbill to the can. I personally never cared much for duckbills, so I only have them in a couple of display regulators. That is just my personal choice.
Luis

Buceador con escafandra autónoma clásica.

User avatar
Bryan
Plank Owner
Posts: 5264
Joined: Fri Jun 24, 2005 11:40 am
First Name: Bryan
Location: Wesley Chapel Florida
Contact: Website

Re: Interesting silicone duck bill issue.

Tue Aug 09, 2016 9:57 am

It's happened to me more than once when using my LaSpirotechnique Mistral with the EPDM hoses. I think it's because they can pull such a strong vacuum. I've never experienced it with regular hoses. Then again I don't use duckbills unless specifically requested by a customer for restoration accuracy. DBE is the only way to go for low maintenance and reliability.
Doing it right should include some common sense, not just blindly following specs and instructions. .Gary D, AWAP on SB

User avatar
SurfLung
Master Diver
Posts: 1508
Joined: Sat Jan 01, 2011 2:03 pm
First Name: Eben
Location: Alexandria, MN
Contact: Website

Re: Interesting silicone duck bill issue.

Tue Aug 09, 2016 11:07 am

- Thanks for the suggestion to glue the duckbill to the can. That would definitely solve it.
- Duckbill inversion happened to my friend Rich's Mistral when I was showing him how to purge the mouthpiece underwater by raising it to cause a free flow. We didn't know what was going on until Sea Hunt Jerry recognized it as an inverted duck bill.
- I still don't know for sure what the cause was. But, gluing it in place would definitely solve it. And, I remember several of the double hose regs I have rebuilt seemed like their old duck bill was originally glued to the can.
SurfLung
The Freedom and Simplicity of Vintage Equipment and
Vintage Diving Technique are Why I Got Back Into Diving.

DAAquamaster
Skin Diver
Posts: 25
Joined: Mon Aug 08, 2016 9:14 pm
First Name: Larry
Location: Winterville NC

Re: Interesting silicone duck bill issue.

Tue Aug 09, 2016 11:13 am

Thanks,

I'll order another DBE in November, and either silicone the duckbill to the can in the interim, or move one of my others ones to the DIN PRAM in the interim if it doesn't stick.

DAAquamaster
Skin Diver
Posts: 25
Joined: Mon Aug 08, 2016 9:14 pm
First Name: Larry
Location: Winterville NC

Re: Interesting silicone duck bill issue.

Tue Aug 09, 2016 11:16 am

SurfLung wrote:And, I remember several of the double hose regs I have rebuilt seemed like their old duck bill was originally glued to the can.
I've never been sure if that was an artifact of being intentionally glued or just the aged rubber sticking to the can. I suspect it was the latter given that I've seen old rubber mushroom valves stick just as hard.

DAAquamaster
Skin Diver
Posts: 25
Joined: Mon Aug 08, 2016 9:14 pm
First Name: Larry
Location: Winterville NC

Re: Interesting silicone duck bill issue.

Tue Aug 09, 2016 11:22 am

luis wrote:
DAAquamaster wrote:
If that's the case, a duckbill eliminator mod is a good idea to go along with the new DSV.

Larry
Even better... an Argonaut is a better choice to go with the DSV. :wink:
If you really want extremely low exhaust flow resistance, try an Argonaut.
I don't know...I think I'd like to stay with my "vintage" PRAM rather than getting one of those new fangled Argonauts. :D

rx7diver
Skin Diver
Posts: 47
Joined: Fri Aug 28, 2015 11:22 am
First Name: Ronald
Location: Columbia MO

Re: Interesting silicone duck bill issue.

Wed Aug 10, 2016 11:08 am

DAAquamaster wrote:
SurfLung wrote:And, I remember several of the double hose regs I have rebuilt seemed like their old duck bill was originally glued to the can.
I've never been sure if that was an artifact of being intentionally glued or just the aged rubber sticking to the can. I suspect it was the latter given that I've seen old rubber mushroom valves stick just as hard.
Thanks, DAAquamaster, for writing about this inverted duckbill valve issue. I don't think I have ever heard/read about this before.

In 1987 or so, I opened up a couple of the double hose regulators used in my open water course's pool sessions. (Semester-long, for-academic-credit, university NAUI course. Sorry, I can't recall for certain what brand/model DH regulators these were.) The rubber duckbill valves all were--or seemed to be--deliberately glued to the cans. Now I understand why!

Safe Diving,

rx7diver

User avatar
Nemrod
VDH Moderator
Posts: 1398
Joined: Sat Jun 25, 2005 1:53 pm
First Name: James
Location: Kansas

Re: Interesting silicone duck bill issue.

Sat Aug 13, 2016 1:42 am

The silicone duckbills will suck back into the hose horn, this has been widely reported (and demonstrated) even with the thin latex duckbills back in the day and was most annoying then as now. A dab of Aquaseal or RTV, depending upon which material, to secure the hose to the can is a good thing to do to prevent that occurrence.

The real solution is the DBEV. I have converted all of my vintage double hose and Phoenix regs to the DBEV. If I ever see another duckbill it might be too soon.

Nem

Return to “Modern Era Double Hose Diving”

Who is online

Users browsing this forum: No registered users and 2 guests