Scubapro chrome plated brass regulators...

[Angelo Farina]

I tried still wouldn't free flow.

A 156 (or 109-BA) must be tuned very low for freeflowing in air. Around 0.7-0.8".
Mine are tuned at 1.1-1.2, and they do not freeflow easily, as I do not like the Venturi "boost", nor regs that free flow too easily.
Normally I keep the knob screwed in by 1 - 1.5 turns, so the cracking effort goes up, above 2 inches, which is just fine for me.
I unscrew the knob only when needed.

 

[Couv]

Thanks

NP....well, you made me go back to my bench to check another just in case I had an oddball. I'm overjoyed to say that example #2 proved to flow just as much, if not more than the first BA-cannot tell how much, as my rotameter is only scaled to 15 SCFM. If I were to interpolate the markings, the disk maxes out at over 20 SCFM. Therefore, these regs are blowing WAY past that.

Specimen #2 will not only freeflow with the tube attached, but also without. In fact, I can get it to freeflow with a sharp breath sans tube.

This is one of my favorites as it has a beautiful 109 cover (it's a BA,) a satin finish, and best of all the exhaust valve is the same size as a G250. It breathes like a dream.
(This way up ---> )

BTW When I use the term Freeflow in the context above-I mean freeflow due to venturi action-not because of too low cracking effort or a discrepancy with the tuning or a valve component.

 

[Umuntu]

This is one of my favorites as it has a beautiful 109 cover (it's a BA,) a satin finish, and best of all the exhaust valve is the same size as a G250. It breathes like a dream.

I haven't paid too much attention to the 109 exhaust valves. Are the later exhaust valves larger than earlier exhaust valves ?

 

[Couv]

I haven't paid too much attention to the 109 exhaust valves. Are the later exhaust valves larger than earlier exhaust valves ?

Almost all 109s and Balanced Adjustables have a smaller exhaust valve than the G series regulators. Only the very latest version BAs have the larger exhaust valve. Every large exhaust valve I've seen was on a satin finish case; but not all satin finish cases have the large exhaust valve.

 

[Umuntu]

Almost all 109s and Balanced Adjustables have a smaller exhaust valve than the G series regulators. Only the very latest version BAs have the larger exhaust valve. Every large exhaust valve I've seen was on a satin finish case; but not all satin finish cases have the large exhaust valve.

Thank you. I will have to look more closely at the exhaust sizes.

I generally don't remove exhaust diaphragms when servicing. They are usually in good shape and I don't want to risk tearing them.

The benefit of the larger exhaust diaphragm would be a lower WOB on the exhale part of the breathing cycle ?

 

[rsingler]

@Angelo Farina hit one nail on the head with his comment about the relationship between cracking effort and ease of freeflow.
@couv hit the second and third nails in noting a case-to-case discrepancy among 109's, and the effect of breathing technique on starting freeflow.

Each 109 was a hand-welded work of art. There were clear differences from reg to reg, and over the years, assorted dents and dings in the case subtly change air flow. That is the magic in today's plastic molded regulators. The consistency in interior shape from regulator to regulator allows similarly consistent performance. Whether that shape was created by CAD design or by trial and error, when it is molded plastic, it is more consistent from item to item. And as you are all discovering with your differing results, it takes very little difference from one case to another to show marked differences in Venturi action at high flow.

Technique in initiating airflow also plays a role, in my experience. If you give the purge button a sharp whack, and initiate flow abruptly, you are much more likely to maintain freeflow than if you ease it forward. I do not know why this should be the case, but suspect it has something to do with how somewhat laminar flow is created inside the case. With abrupt opening, the instantaneous airflow may be closer to the crossover point between negative resistance to France positioning and freeflow, measured with a dynamic evaluation.

The discussion of Venturi vanes and angles all relates to how air exit via the mouthpiece is maintained. The proper angle helps maintain a somewhat laminar flow. Angles that differ from optimal create turbulence which disrupts the Venturi action creating the decreased pressure that keeps the valve open. That decrease in negative pressure (shift towards zero) allows poppet spring pressure to play a role. Once cracking effort exceeds the negative pressure induced by Venturi outflow, the valve wants to close.
Conversely, the higher the cracking effort, the more difficult it is to create enough negative pressure inside the case due to Venturi action to keep the valve open.

Now, all of this is moot unless Venturi-induced assisted valve opening is important in real-world diving. Clearly, if case geometry fault helps reduce effective cracking effort in most diving positions to near zero, it really doesn't matter near the surface.
But where I think all of this Venturi assistance might indeed matter is at depth. @Luis H can likely help us here, but it is my prejudice that at depth (say, 100 feet/4 atm), normal peak air flows of perhaps 2 SCFM are roughly equivalent to 8 SCFM measured at the surface. Hence, seeing what happens to valve opening resistance with dynamic flow measurements at 8 SCFM is indeed relevant.

 

[Umuntu]

From the text of the patent:
"FIG. 3 is a longitudinal section through an embodiment of second-stage valve which has a manual arrangement for adjusting the counteracting flow, once again conforming to the improvement made by the present invention,"

"As has already been stated in the introduction to the present description of the drawings, the other main feature of the invention lies in the possibility which exists of making a direct adjustment, by a manual operation, to the counter-pressure flow in the second stage of the two-stage pressure reducer."

"FIGS. 3, 4 and 5 of the accompanying drawings illustrate a preferred embodiment of valve for the second stage of the reducer. This valve, which has already been mentioned by its general reference 3, continues from a tube 19 for connecting to the flexible hose 4, the considerations applying to this tube being the same as those already set forth as applying to the similar tube belonging to the high pressure valve 2"

So this patent describes two innovations:
- at first stage, the user-controllable IP,
- at second stage, the knob for controlling the Venturi effect.

The VIVA patent is quite different, of course.
But the purpose remains the same, to give the user some control on the Venturi effect, which was not possible in the original "offer regulator" invented by Raimondo Bucher around 1960, nor in Pedersons's patent, which is similar to Bucher's (unpatented), but rotated 90° (probably because there was prior art on the fixed vane in its "natural" position).

It is an interesting patent application. It discusses using a venturi tube (similar perhaps to that in current Mares regulators), but not a venturi vane, and it sought a patent for using an adjustable counter-acting air jet to regulate the venturi effect.

This part of the patent application was not upheld, and so there is only one claim in the US patent granted. It was however probably originally part of the patent application, hence the drawings and the description.

I was not familiar with Raimondo Bucher, and I looked him up as a result of you referring to him. He was truly an impressive man with interesting achievements. Thank you for sharing his history.

 

[Luis H]

@rsingler it doesn't sound like you have ever dove a regulator that didn't have any venturi assistance, like an old Broxton ave double hose.

Every regulator in existence today has some level of venturi assistance at all depth. If you even dive an old Navy DA or any of the old Broxton regulators you will understand what I am talking about.

Even if you are on your back with possitive pressure breathing, the air delivery is always proportional to how much you are sucking (suctioning). In the correct position (with the center of the diaphragm low enought) the cracking effort can be zero (or less), but to keep the demand valve open, you have to demand the air.

When you have no venturi at all, after the demand valve cracks open, you have to increase the suction level to get any flow and the flow is proportional to how much more the suction level increases. It is just a nice linear relationship were flow is directly proportional to suction level.

 

[Open Ocean Diver]

Almost all 109s and Balanced Adjustables have a smaller exhaust valve than the G series regulators. Only the very latest version BAs have the larger exhaust valve. Every large exhaust valve I've seen was on a satin finish case; but not all satin finish cases have the large exhaust valve.

Do you have a measurement I’d like to check my 156 and 108HP?

 

[Couv]

Exhaust Valves:

26mm fits Scubapro metal 2nd stages 108,109, and the majority of BAs (usually blue)

33mm fits Scubapro G250 (all G series I think) and very few Balanced Adjustables. (usually black, sometimes clear)