Adding a Second stage shutoff valve

[Anony]

I want to add a shutoff valve to my second stage regulators.
I had this idea yesterday, and I just finished drawing a few diagrams to see if it seemed feasible.

Why a shutoff valve:
When a regulator starts to freeflow at 30ft with a buddy nearby, it is safe to breath off it and do a safety stop, but what if you are at 130ft and you are breathing a special gas? That special gas may be absolutely necessary to your survival. Shutting off the bad reg and breathing from the octo could easily save your life.
Or what if you are simply at 100ft with plenty of air and the spare starts to freeflow?
You may not have enough air to complete a safety stop, by the time you get up to 15 ft.
The point is: A freeflowing regulator is a dangerous waste of air, and it can be stopped quickly and safely, allowing a diver to use the octo to safely end the dive.

Where, and what kind of valve:
I envision a twist-top on/off valve on the stage 2 hose, between the lp hose and the LP seat.
However, while writing this I realized that one might use a valve that lets you limit the air flow without stopping it, possibly allowing a freeflow to be turned down to a safe, breathable trickle, in the event you do not have an octo for some reason (I dont know if technical divers have octos on every tank, and this seems especially good for them.)

Possible problems:
1.Leaving the octo off could kill a dive buddy
2.If the first stage is causing the freeflow, shutting off both valves could cause explosion.
3.Accidental closure might scare the living daylights out of you.
4.It is an added point of failure.

My opinions/solutions
1. In the event a diver needs your air, give him the working one and THEN turn on the octo. Obviously you should never start the dive with a freeflowing reg turned off. It is an emergency solution only.

2.This should be explained to any diver attempting to use shutoffs. This also seems like a reason in support of shutoffs:If both regs are freeflowing, shutting off one may save enough air to protect the diver.

3.Why would you ever start a dive without checking the regs? and if you closed the valve during a dive, perform normal emergency procedures: Grab an octo and THEN sort out the problem. No real problem here.

4. An added valve IS a point of failiure. There is no way around it, however I think that the chance to save vital air outweighs the added trouble spot.


Opinions? Problems I didnt spot? Solutions that dont add up?

 

[Web Monkey]

I want to add a shutoff valve to my second stage regulators.
I had this idea yesterday, and I just finished drawing a few diagrams to see if it seemed feasible.

Why a shutoff valve:
When a regulator starts to freeflow at 30ft with a buddy nearby, it is safe to breath off it and do a safety stop, but what if you are at 130ft and you are breathing a special gas? That special gas may be absolutely necessary to your survival.
. . .

Opinions? Problems I didnt spot? Solutions that dont add up?

Most "second stage freeflows" are actually first stage freeflows, and blocking off the second stage will either blow the hose or cause something else to freeflow (like your alternate.

If you're having problems with freeflows, what you really need is a regulator that's appropriate for the conditions and that has been kept serviced.

Terry

 

[jtadrenaline]

I like your open train of thought. I do not, however, think it is a neccessary addition. With a properly serviced and tuned set of regs, you should have very few free flows. The intermediate pressure should be set correctly and the secondary pressure of the octo should be such that it is slightly harder to pull the diaphram breaking pressure to draw air. As techs, we do this intentionally to help prevent too many freeflows. Most main second stages these days have an adjustable knob on the side to regulate breaking pressure and some even have an adjustable airflow gate. With most manufacturers, the specs state to set it so it will just start to freeflow at adjustment to full stop on the knob, that will allow you the easiest breathability with plenty of adjustment left in the other direction.
Your best and easiest way to stop a freeflowing regulator is to simply stick your finger in the opening of the mouthpiece when it is freeflowing. This instantly builds the pressure back on the diaphram and stops the hiss. Forget the turning it upside down and shaking or tapping it. I just see too many things that could go wrong with a shut off valve....Most of the time, if you need to hand off a reg to someone or switch over to your octo, you are already in an elevated excitement state (near panic in some cases) and don't want to add yet another step in an emergency situation.
I hope this information was helpfull, it was not meant to try to put down your idea, just a observation.

JT

 

[Anony]

Cool, Thanks for the feedback.
To webmonkey:
Can you back up the claim that most failed-regulator freeflows are due to the first stage?
I'd love to know for sure.

Jtadrenaline:
Thanks for the informative post, but I didnt intend this as a way to stop the normal -sensitive reg- freeflow. It in an idea for regulators that fail, and then begin to freefllow.

edit: The more I think about this, the more I think it is not necessary. I've yet to see a second stage fail in any manner, much less by freeflow. I suppose I'll scratch this for now, at least until I see an actual reg fail.

 

[jtadrenaline]

In 18 years of diving, I have not seen too many problems with regularly serviced regs. The first stage is commonly to blame for free-flows, but the secondaries are just as much. I'm all about making things better, but have never seen the need for a shutoff. Most first stage pressures are set around 147 psi +/- 5 lbs. Second stages can get sand and grime in them, but rarely fail because of it. The system remains closed until air is pulled off, when air is flowing....nothing gets inside due to the pressurized air coming out (you can even puke through them as I've seen plenty of students do (they bring in all the fish with the chunder chum). Regulator systems are made to free flow instead of locking up in the event of a malfunction. This is a good thing. I still suggest that you get yours serviced every year, it's a life support system and regular servicing is the cheepest form of insurance. In answer to the last question....I don't recall ever seeing a total malfunction of a regulator under normal curcumstances (aside from extreme testing). Inspect 'em, get 'em serviced, have fun diving.

 

[Anony]

Thanks for your informative posts JT, I will service my regs, and I will put this idea on the backburner until I actually experience some freeflows.

 

[do it easy]

edit: The more I think about this, the more I think it is not necessary. I've yet to see a second stage fail in any manner, much less by freeflow. I suppose I'll scratch this for now, at least until I see an actual reg fail.

Freeflows happen, but I think there are better ways to deal with them: Web monkey already mentioned properly tuned gear. You could also carry redundancy and build a safety margin into your gas plan.

In your examples, if a particular gas is essential to your survival, then you should have enough in reserve, preferably, in an independent system. This could be a suitably sized pony bottle, doubles, and/or a buddy.

Also, I think Apeks makes something similar to what you were thinking of- Freeflow control device.

 

[Jimmer]

Zeagle Systems - Scuba Diving Equipment Manufacturer I own one, but haven't used it in ages. It just sit there in my spare parts box. It's a slide valve as opposed to a 1/4 turn ball valve. It is very easy to use, but I see it potentially being an issue like you said, if someone grabbed an octo and didn't know how to operate it. I have considered putting it on my bungee'd backup on my single tank rig, since if it was to freeflow, the only way to stop it is to shut off the tank valve, but with my second stages properly tuned, I dont forsee this being an issue.

 

[Web Monkey]

Cool, Thanks for the feedback.
To webmonkey:
Can you back up the claim that most failed-regulator freeflows are due to the first stage?
I'd love to know for sure.

That's the only kind we get in cold water.

There are second stage leaks, which are caused by dirty or improperly serviced second stages, but these don't really become freeflows until the continued leak cools the first stage enough to freeze it open.

It's also possible to have your second stage open up if you're facing it into a stiff current, however your device wouldn't be much help there either, since turning off the second stage means you can't breathe.

If your second stage is serviced and kept clean, it should be fine.

Sorry about your valve, but I just don't see much of a market for it.

Terry

 

[300bar]

A second stage shut off valve is indeed not a good idea.
while in (very) cold water you can have a freeflow from either stage.
The most common reason for a freeflow is a (major) failing of the HP seat.Your 2nd stage will than act as a relieve valve.Shutting that down will result in a hose blow out.