A700 Schematics diagram?

[tbone1004]

then I stand corrected. I thought the spring pressures were adjusted to where when the purge button was released the freeflow would stop. The purge buttons must depress farther than most of the regulators I'm used to working with.

 

[Pavao]

then I stand corrected. I thought the spring pressures were adjusted to where when the purge button was released the freeflow would stop. The purge buttons must depress farther than most of the regulators I'm used to working with.

Well, yes, this is correct, except where a Venturi Effect is present, and in simple terms, that's all it is, it's designed to counter act the spring force. That's one of the things that makes an easy breathing reg... an easy breathing reg.

When air flows, it creates a vacuum just behind the diaphragm, which pulls the diaphragm inwards, which in turn depress the lever that compress the spring, thus keeping it open and continuing to let air out. When it's set to "predive" mode, all it's doing is directing the flow inside the 2nd stage in a direction to which a vacuum is not created, that's all that is to it.

When I sell a reg to a first time buyer, I make sure I demonstrate this to the costumer, hook up the reg to a tank and make it freeflow, freeflowing regs are always loud, if you aren't used to it and wasn't expecting it to happen, it's predictable to see a reaction as if something went wrong/blew up, gently slide a finger in front of the mouthpiece opening and it will stop, because it breaks that direct fast air flow and restores the pressure inside the 2nd stage, filling the vacuum space.
That's one of the first things I'd explain to my OW students just prior to entering the shallow water for their first confined pool session also, it's bound to happen, someones reg will hit the water the right(wrong) way and free flow, it's a lot less stressful for them once they understand why it's doing it and how to make it stop.

If I had a dollar for every costumer that comes in complaining their reg is faulty because it freeflows...

 

[tbone1004]

Pavao, you should see the looks I get with inexperienced divers when I pressurize my Poseidons

 

[Hickdive]

Well, yes, this is correct, except where a Venturi Effect is present, and in simple terms, that's all it is, it's designed to counter act the spring force. That's one of the things that makes an easy breathing reg... an easy breathing reg.

When air flows, it creates a vacuum just behind the diaphragm, which pulls the diaphragm inwards, which in turn depress the lever that compress the spring, thus keeping it open and continuing to let air out. When it's set to "predive" mode, all it's doing is directing the flow inside the 2nd stage in a direction to which a vacuum is not created, that's all that is to it.

When I sell a reg to a first time buyer, I make sure I demonstrate this to the costumer, hook up the reg to a tank and make it freeflow, freeflowing regs are always loud, if you aren't used to it and wasn't expecting it to happen, it's predictable to see a reaction as if something went wrong/blew up, gently slide a finger in front of the mouthpiece opening and it will stop, because it breaks that direct fast air flow and restores the pressure inside the 2nd stage, filling the vacuum space.
That's one of the first things I'd explain to my OW students just prior to entering the shallow water for their first confined pool session also, it's bound to happen, someones reg will hit the water the right(wrong) way and free flow, it's a lot less stressful for them once they understand why it's doing it and how to make it stop.

If I had a dollar for every costumer that comes in complaining their reg is faulty because it freeflows...

This, and your previous posts in this thread explain it perfectly.

I now show customers this happening to try to prevent them coming back with new or just-serviced regs to complain when they are in fact working as designed.

Many years ago I got a reg back from service that didn't do this and when I pointed it out the the tech told me that he was so fed up with people not understanding that he purposely left regs badly tuned to save people bringing them back. The fact that they breathed like donkeys as a result was beside the point!

 

[axxel57]

The presence of a full constant free flow when pushing the purge button for me is not a sign of quality but a design flaw.

A well adjusted Venturi should free flow only a moment and then stop.

It seems to be too time consuming and cost intensive for most manufacturers to develop a venturi for their 2nds which does exact that when you're in the dive mode.

A full constant free flow after pressing the purge button means a very strong venturi override, which could cause a bad force feeding of air for a diver.

The R190s and R295s are notorious for that. I hate it if I test the regs on the flow bench and I cannot even closely reach the 5 SCFM range without a violent venturi override. Often not even the switching of the flow vane in the opposite direction solves the problem.

As a diver with a 2nd with an adjustable venturi you should adjust it to a point were the venturi override just kicks in but stops instantly after that.

That's one reason I love my SP Ds. I can adjust them to the point it should be and that's it for long time.

A 2nd stage that free flows constantly after pressing the purge button on the surface might show you that the venturi is working, but diving with it without adjusting it correct might just increase in certain situations stress, might cost you unnecessarily air while diving and shows a lack of understanding how a venturi should work.

Sometimes I have the feeling that hardly any diver knows why and how to adjust the venturi in his 2nd (if possible) and enough specialists think the stronger and faster a venturi overrides the valve mechanism of the 2nd stage the better performs that 2nd stage.

I don't think so.

 

[Pavao]

Some people really "know" a lot, they "know" even better than the people who designed the thing in the first place, it's amazing, really!

I had a diver once show up with a BP/W he had bought online, used, he too was complaining about it's design "flaw" it "clearly" had, he thought the BP was backwards since it was awkward having to attach the tank to the convex side of it, so he turned it around, now the concave side offered a groove and stable platform for the tank, while the convex side seemed to be made to fit the back of a human.

What a brilliant guy, in a very short time he was able to identify a problem these stupid manufacturers have been missing after years of working with it and he fixed their flaw design with a simple adjustment.

Now, believe me, I did try, hard I should add, to show him the right way it should work, but I can tell you, the guy is pretty convinced I do not understand how it should work.

Just had to shake my head and walk away...

 

[cool79]

After seeing so many tech talk, I am getting confused. So when on surface, after purging for a few sec in dive mode, it is okay for it to be in free flow mode or not?

 

[axxel57]

@cool79

If you want to find out if your Venturi assist is working, then you open your Venturi adjuster to max and press the purge button.

If a constant strong free flow is developing, you know your venturi is working.

From the engeneering point of view for most of the manufacturers it is, how I understand it , pretty challanging to develop a 2nd in mass production which is showing the optimal performance of a venturi piece by piece and adapted to each dive profile.

So like for most components of a regulator the result is not supposed to be exact on the point, but there is a tolerance range within the the specs which has to be adjusted to perform to its best result.

That's the same for most adjustable Venturi assists on the market.

In the technician courses of the early 90ties this was still explained and taught how to adjust a Venturi for optimal performance (it's simple enough).

The technician courses I had to conduct in the last 20 years don't teach that anymore, this is why some guys who attended a couple of those clinics seem to have no clue about it.

An adjustable Venturi is adjustable, not only for on and off for a reason.

The attitude of this guy in the story with the lousy adjusted regulators to avoid discussions about their free flowing regulators with his customers instead of explaining and adjusting them reflects quite exact the quality of those clinics by most of the manufacturers.

This is one reason I try to support the DIYers in this forum.

Mostly I blame the manufacturers for their lousy courses, but I also think that it is a good attitude of a scuba technician to show passion and the desire to learn more about the functions of the things they are working with.

Sometime I have the feeling I see more often this passion and desire among the 'amateurs'.

My impression is that over the last decades the Venturi have become more and more effective, but also stronger. I guess that the manufacturers simply want better ANSTI results, like nowadays the emphasis seems to be more on the development of more effective exhaust valves instead of better inhaling qualities.

Back to the adjustment.

What you have to do to get optimal results from your adjustable Venturi is pretty simple.

You put the regulator on a tank, open the valve. If at pressing the purge button the Venturi overrides directly the 2nd stage mechanism you stop it and close the adjustment knob (or in the case of the A700 move it towards the Pre Dive position) step by step repeating the procedure until the Venturi is just not starting to free flow or until it stops on its own after one or two seconds of free flow.

So now, anyway how strong the Venturi works, it should prevent air force feeding, should avoid air loss by free flow and should be working with the best results over the course of a dive.

Good luck.

 

[ams511]

After seeing so many tech talk, I am getting confused. So when on surface, after purging for a few sec in dive mode, it is okay for it to be in free flow mode or not?

It is ok.

Not to confuse the issue but not all regulators will do this. In my experience, Scubapro regulators tend to have a stronger venturi effect than some other brands.