Conservative Tech?

[herman]

I would suggest you look for a US Divers Conshelf or better yet a SEA, which is almost the same design as the MK-11. The basic principals are the same for those regs as they are for the MMK11-17, manuals are easy to come by and VDH has all the parts.....and when your are done with it, you will have a solid, battle tested reg I would dive anywhere. They show up on ebay or Craigs list all the time for little money.

 

[buddhasummer]

I have a near mint con 21 freshly serviced in the classifieds.

 

[Ojai Diver]

More basic questions: Is the A 700 a balanced second, and what does it mean for a second stage to be balanced?

Also, am I correct in assuming from these posts that if I get a free flow at depth, or excess air, I can control this by the adjustment knob?

I also understood the venture vane +/- was to prevent surface free flows only. Thanks.

 

[Couv]

Yes, your A700 is a pneumatically balanced second stage. To understand more about balanced vs. unbalanced designs, see @halocline 's excellent explanation here:
Balanced vs Unbalanced Scuba Diving Regulators

You may or may not be able to control a freeflow at depth depending on the cause. If the cause is a runaway intermediate pressure, most likely not. If the freeflow is caused by venturi, yes-by biasing the flow vane to block some of the flow. If the freeflow is caused by regulator position in the water column the adjustment knob is the proper control. If the seat has minor wear causing a freeflow (you would notice this at the surface) the adjustment knob may be all that's required, but an adjustment of the orifice is really what is called for or a seat replacement.

 

[Ojai Diver]

You may or may not be able to control a freeflow at depth depending on the cause.

Thanks, couv. I enjoyed the article, too.

By "runaway intermediate pressure" do you mean one that keeps going up and up, in other words, IP creep?

I am just wondering if I should be concerned if the tech's recent adjustments may cause an uncontrollable free flow on a deep dive with low tank pressure. It's fine if I can control such a free flow with the knob or the vane. But not fine if I can't.

Also, is it correct to say that closing the knob reduces the volume of air entering the second stage? Thanks!

 

[halocline]

I forgot all about that article....I wrote a few of them several years back for Natalie at underthejungle. She was managing some website that I guess no longer exists but the articles must have been transferred. They were supposed to be as simple as possible. I had a 'nom-de-plume' as well, Koby-Ashi Maru.

Anyhow, don't worry too much about an uncontrolled free flow as long as your IP is steady, as you referred to. Usually you can stop free flows simply by putting your thumb in the mouthpiece opening and stopping the flow of gas. It's a good thing to practice sometime when you're hanging at a safety stop. Switch to your alternate 2nd stage, point the mouthpiece of the primary 2nd towards the surface, and tap the purge if it doesn't start flowing on its own. Once it's roaring away, stick your thumb in the mouthpiece and turn it pointing down. It's a handy thing to learn to be quick at.

It's not quite correct to say that the breathing resistance knob changes the volume entering the 2nd stage. What the knob does is increase the spring tension so that it takes more force to open (and keep open) the valve through which air flows. This makes the reg less likely to free flow, but also requires more effort to draw air. You can still get the same flow.

 

[Couv]

Also, is it correct to say that closing the knob reduces the volume of air entering the second stage? Thanks!

What Koby-Ashi Maru ^^^ said, until Captain Kirk says otherwise.

 

[buddhasummer]

"Over Balanced" DS4 with Conshelf 14 tuned to 1.1" at 33 meters no I'll effect, so a supposed increase of around 5psi made no difference. I'll try it at 40.