question for Atomic users

[Hatul]

Recently I got the Atomic ST1 and have a question about the adjustment knob on the second stage.

In my old Oceanic when I turn the knob to the extreme counterclockwise the reg would freeflow. But in the Atomic even at the extreme lightest cracking pressure the reg does not freeflow. Is this normal or does the reg need adjustment?

Adam

 

[Dry_Diver]

I dive with the Atomic B2. It is not the same reg, but has the same knob with the same function.

The knob that you are referring to is the AFC (anti flow control) knob. Its purpose it not to make it easier or harder to breath from, it is to allow you to be able to control the pressure that is needed to "crack" the reg.

I dive with mine turned fully counter clock wise. If you find yourself swimming into a current and the reg starts to free flow because of the increased pressure on the face of the 2nd stage, by turning the knob clockwise (I usually go a half turn at a time) it will prevent this from happening.

I know that my answer is probably not the most technical but I hope that it answered your question.

You got a great little reg there, I have loved mine from day one.

 

[Hatul]

I dive with the Atomic B2. It is not the same reg, but has the same knob with the same function.

The knob that you are referring to is the AFC (anti flow control) knob. Its purpose it not to make it easier or harder to breath from, it is to allow you to be able to control the pressure that is needed to "crack" the reg.

I dive with mine turned fully counter clock wise. If you find yourself swimming into a current and the reg starts to free flow because of the increased pressure on the face of the 2nd stage, by turning the knob clockwise (I usually go a half turn at a time) it will prevent this from happening.

I know that my answer is probably not the most technical but I hope that it answered your question.

You got a great little reg there, I have loved mine from day one.

OK. So I gather the Atomics normally do not freeflow regardless of the adjustment (except in the situations you describe) . This may have to do with the seat saver, since on the Oceanic when you put the reg away you want to turn the knob to remove pressure on the seat, while on the Atomic it's not necessary.

Adam

 

[Dry_Diver]

Sorry I was not clear,

If you drop your reg in the water mouth piece up it will free flow. Adjusting the knob will not keep a free flow from happening in the position that I stated above. Hope that clears things up.

The situation that I described above isn't really a free flow, it is more that the water moving in the current is in a way pushing the purge button on the reg for you.

 

[Akimbo]

I dive with the Atomic B2. It is not the same reg, but has the same knob with the same function.

The knob that you are referring to is the AFC (anti flow control) knob. Its purpose it not to make it easier or harder to breath from, it is to allow you to be able to control the pressure that is needed to "crack" the reg.

I dive with mine turned fully counter clock wise. If you find yourself swimming into a current and the reg starts to free flow because of the increased pressure on the face of the 2nd stage, by turning the knob clockwise (I usually go a half turn at a time) it will prevent this from happening.

I know that my answer is probably not the most technical but I hope that it answered your question.

You got a great little reg there, I have loved mine from day one.

OK. So I gather the Atomics normally do not freeflow regardless of the adjustment (except in the situations you describe) . This may have to do with the seat saver, since on the Oceanic when you put the reg away you want to turn the knob to remove pressure on the seat, while on the Atomic it's not necessary.

Adam

Maybe the video and text on this page will explain better. See the Automatic Flow Control video and click on "Patented Automatic Flow Control (AFC) on the bottom. The seat saver is a separate and unrelated function also explained on this page.

Atomic Aquatics Second Stage Regulator Design

Consider what happens when the regulator is out of your mouth and you jump in the water. If the second stage housing does not fill with water, water pressure can depress the diaphragm (like pressing the purge). Air will flow, often so fast that water cannot enter the housing to equalize the pressure, so it continues freeflowing until you fix it.

There are two uses of manual knobs and levers on second stage regulators. Some are adjusting knobs used to change the spring pressure on the seat. This can reduce cracking pressure to the point of freeflow, or increase breathing resistance so it is less likely to freeflow against a head-on current. Some levers or knobs also control a vane, venturi, or paddle to create turbulent flow. Some have both.

This link discusses the features in a little more detail:
http://www.scubaboard.com/forums/5336554-post8.html

What most people actually use the adjustable spring pressure for is to crank down the sensitivity so it does not freeflow when the regulator is out of their mouth — most often a problem on an octo when entering the water or when you are exiting the water. The disadvantage is the adjustment range is pretty narrow so you may not notice the higher resistance. As a result, you have unnecessarily high inhalation resistance throughout the dive.

Atomic uses the AFC (Automatic Flow Control) to minimize this conundrum and set the cracking pressure/inhalation resistance to a predetermined optimum setting. Basically, a metal arm sits in front of the gas jet on the surface to cause turbulent flow at high flow rates. Turbulent flow forces pressure to slightly increase, acting against the inside of the diaphragm, so small pressure differentials do not cause uncontrolled freeflow.

Naturally this compromises the regulator performance near the surface, but a separate small diaphragm (node above the knob) activates the lever to automatically move it out of the way at some shallow depth where it is no longer needed. The knob is used to override the automatic setting, not change the spring pressure on the seat.

As Dry_Diver explained, forcing the AFC lever into the flow with the knob effectively reduces sensitivity to head-on currents, due to turbulent flow. Because the spring pressure is preset, maintaining the seat in optimum condition is more important than on a regulator where you can increase spring pressure to overcome seat wear. That is where the "Seat Saver" comes into play. The idea is all the time the regulator is not pressurized; the seat is retraced so it does not "take a set". Atomic engineers believe this keeps their regulators in better tune over a longer period of time. It certainly seams logical though I don't have enough personal experience repairing them to say.

 

[Hatul]

Thanks for the info. Also correct me if I'm wrong but I believe the second stage of the T2, ST1 and B2 are identical aside from the front logo.

Also, some have reported switching from the second stage swivel hose to a Miflex hose. Anyone know the procedure for doing this and is this something I can do myself or does it have to be done by the shop?

Adam

 

[a22shady]

I dive the Atomic M1's and I have the Miflex hoses. Not sure with Swivel but regular hose Switching them is the same as any other. As far as the free flowing technically no regs are set up to free flow from the factory even with the adjustment all the way out. However some people prefer it like that and it can be set that way from a diveshop or trained person that knows how to work on reg's. Me personally I do not like it to free flow but everyone has there own prefrences

 

[Akimbo]

Thanks for the info. Also correct me if I'm wrong but I believe the second stage of the T2, ST1 and B2 are identical aside from the front logo...

My understanding is the geometry on all Atomic regulators is identical, except for an optional first stage swivel on the Z2. Only materials and labeling change. From what I have seen, the Ansti simulators tests are also the same, within normal manufacturing tolerances, and all exceed minimum standards in all phases for EN-250 and the US Navy.

Atomic Aquatics Regulator Systems Comparison Chart

Atomic Aquatics Regulator Specifications

 

[redacted]

I believe most regs that have user adjusted cracking pressure are tuned for maximum performance, short of a leak with the adjustment knob in the easiest breathing position. Oceanic is the exception as it call for that tuning to be done with the adjustment knob set in a more central position which should result in a slight leak at the surface.

 

[Akimbo]

I believe most regs that have user adjusted cracking pressure are tuned for maximum performance, short of a leak with the adjustment knob in the easiest breathing position. Oceanic is the exception as it call for that tuning to be done with the adjustment knob set in a more central position which should result in a slight leak at the surface.

When Scuba manufacturers first copied "Dial-a-Breath" feature from the Kirby-Morgan design, most would adjust it to freeflow on minimum spring pressure (in my experience). A lot of complaints started to come from people who didn't understand its proper use, both because it would freeflow and be hard to breathe at the adjustment extremes. I have noticed that the adjustment ranges have become narrower over the years, to the point that it requires a lot of concentration to optimally adjust it.

If used according to the original intent, and is still used in commercial diving, the spring pressure is reduced until freeflow is detected and then tightened just enough to stop. This is a simple and clear indication that it is extremely close to minimum cracking pressure.

The "Dial-a-Breath" feature is necessary in surface supplied diving because the supply pressure at the diver is not automatically adjusted to a constant over bottom pressure. The gas comes off an air compressor or is manually reduced with an industrial regulator connected to high pressure gas banks. As a result, the "Dial-a-Breath" is typically adjusted to its highest tension at the surface and reduced as the diver descents — because the relative supply pressure (over bottom pressure) at the diver is reducing as depth increases.

My personal opinion is the narrowing of the adjustment range so it does not freeflow has rendered a marginally useful feature on a Scuba regulator to nearly useless.