My new G250Vs and ramblings

[Geo7]

Honest question related to that: Do the 109 and 156 Scubapros that lack a vane usually freeflow if the purge is pressed firmly?

 

[buddhasummer]

Honest question related to that: Do the 109 and 156 Scubapros that lack a vane usually freeflow if the purge is pressed firmly?

@couv

 

[lexvil]

Honest question related to that: Do the 109 and 156 Scubapros that lack a vane usually freeflow if the purge is pressed firmly?

If memory serves mine always did if set to hot.

 

[buddhasummer]

If memory serves mine always did if set to hot.

That is my recollection too but it's been a while and I cannot be positive.

Same with a Conshelf 14 if hot.

 

[buddhasummer]

Just as a comparison, a G260 will VFF with mouthpiece on even with higher end cracking effort.

 

[rsingler]

Honest question related to that: Do the 109 and 156 Scubapros that lack a vane usually freeflow if the purge is pressed firmly?

My 156's upgraded to the S-wing poppet usually freeflow just fine with a bang on the purge.

A 109? Most of mine don't unless tuned lighter than I'm comfortable with a downstream second. I attribute that to the heavy 109 spring.

216 on top; 109 on bottom

Theoretically, it shouldn't make a difference, because the balance forces are added to the lighter spring. But somehow, I don't get the same results with the downstream version.

@couv ?

 

[Couv]

A 156 when tuned properly (or a little lower than specs) will definitely VFF. I'll have to double check the 109. But Rob brings up an interesting point. The mechanical spring is stronger in the 109, but if we add the pneumatic force to the mechanical spring in a 156 it stands to reason the total force must be the same-else the IP would overcome the low spring pressure.

 

[Couv]

As @Open Ocean Diver points out, this is a subtle effect. Maybe instead of @couv 's airfoil, we have something as inelegant as a barn door.
In one position, the barn door is more in the way of airflow than in the other, and causes more turbulence, less vacuum and hence no freeflow.
View attachment 635043
The vane above has a semi open side (crescent) and a flat side. Maybe it's as simple as whether the deflector is a little forward, or a little aft in the airflow.

If Rob's picture is representative, then (looking at the lower drawing) it could just be a matter of more blade aft directs air further down the mouthpiece shank. Longer fins, like a freediver wears, move water in a straighter line and further back than say a jet fin. Putting the crescent toward the back may relieve the flow-like a spit fin.

Edit: I'm a little better artist than Rob, so have a look at this picture I just drew. ;-)
Notice where the air from the aspirator hit the vane?

 

[lexvil]

A 156 when tuned properly (or a little lower than specs) will definitely VFF. I'll have to double check the 109. But Rob brings up an interesting point. The mechanical spring is stronger in the 109, but if we add the pneumatic force to the mechanical spring in a 156 it stands to reason the total force must be the same-else the IP would overcome the low spring pressure.

I always looked at the balance feature as an assist to closing on these

 

[lexvil]

If Rob's picture is representative, then (looking at the lower drawing) it could just be a matter of more blade aft directs air further down the mouthpiece shank. Longer fins, like a freediver wears, move water in a straighter line and further back than say a jet fin. Putting the crescent toward the back may relive the flow-like a spit fin.

This is only my perception but since the BA has a very strong Venturi the viva vane was added to disrupt flow and assist in limiting free flow.