Poppet lift

[luE]

Is more poppet lift always better?

My G250's are setup with the lever feet horizontal up against the square broach in the airtube, with the feet bend to match the lever height with the diaphragm, to utilize the full potential of poppet lift. This is also the case with my G500's, and my Atomics also just matches the lever height with the feet being tugged right up against the square broach from the factory. All benefit from the greatest potential poppet lift.

Then, when I look at my Apeks regs, XTX and ATX, they are set to the highest possible lever height, right up against the diaphragm. But the angle to the broach is no way near zero degrees. More like 15 degrees, wasting potential poppet lift. This could of course easily be fixed by bending the feet. But it is always beneficial with more poppet lift? In the case of Apeks regs i would think that if you bend the feet to the the zero angle, it would require more cracking pressure, to not fully free flow with just a single tap on the purge, instead of the rapid activation normally required.

What do you guys think?

 

[Mobulai]

Yes!

Idk why the levers are 15deg off but that doesn’t sound good for the reasons you mentioned; theoretically bending them would be better but it might fatigue the lever legs and they’d crack

Would love to hear @rsingler thoughts on this

 

[happy-diver]

Obviously with some understanding one should do the thing whatever the thing is and work out the details later

 

[rsingler]

You bring up a great question.
Since it gives me yet one more opportunity to criticize the greatly overrated Apeks XTX50, I appreciate it!

The short answer is, as @Mobulai noted, yes! More potential poppet lift is better. The lever foot should be vertical against the left side of the square broach in the barrel for optimum performance. Apek's inability to provide that is a(nother) design flaw. Whether or not to bend the lever feet to accomplish that is a risk/benefit question, due to the risk of creating a fracture in the metal of the lever.

Let's drill down:

With a modern lever design, the curved top allows the lever arm to remain (relatively) constant, while allowing maximum deflection from closed to maximally open (i.e., lever flat against the barrel). In the case of Apeks, that's about 50 degrees of angular change. That angular change at the lever is the same as the resultant angular change at the lever foot.
But as you can see, as the lever drops in 15 degree increments, the rightward shift of the top of the lever foot where it engages the poppet decreases. If the first 15 degrees is 100% movement (actually sin 15, or .258 of the height of the lever foot), then the last 15 degrees is only 3.4% of that. The good news is that we only have to be concerned with 50 degrees total angular change, so the rapid falloff in lever effectiveness at 75 degrees never comes into play.

This is an optimally tuned Apeks XTX 50 barrel. It is possible to seal the valve with the lever foot vertical (and the lever higher), but only before you screw on the faceplate. As you screw down the faceplate, the purge mechanism impinges on the lever, opening the valve.
This design flaw of insufficient case geometry to accomodate a fully erect lever results in about a 12 degree angular drop in the lever before the valve is sealed with the lever right up against the back of the diaphragm disc.

Using Apeks stupid "Flow/No Flow" lever height tool, it's even worse. But with this case, you can get about 50 degrees of angular change.

As the first diagram above suggests, a 50 degree angular change from 0-50 creates poppet movement that is ~77% of the height of the lever foot. However (using the sin of the angular change), the poppet movement of a 50 degree angular change from 12-62 degrees is only 68% of the height of the lever foot.
In other words, this sloppy mechanism (68/77) costs you about 12% of your maximum possible valve opening. Bending the lever arms over with the feet trapped (as we used to do all the time with @herman 's tool with the G250) would allow you to have a vertical lever foot and get that extra 12% of maximum valve opening.

Note 1: Bending the lever foot may be ill-advised if the metal is more brittle than the old G250 material.
Note 2: The number of times you need maximum valve opening during a dive at maximum gas density during a maximum effort emergency is a very small number. Getting an extra 12% poppet movement (because it's poppet lift x circumference of the orifice that determines flow) may not be significant in the grand scheme of things.

On the other hand, thank you for the opportunity to critique this very average design.
To fix this problem, my choice would be to buy a different regulator.

 

[happy-diver]

Is this a picture of how far out it is

No bend no balls no answer

 

[rsingler]

Yes

 

[luE]

Ok. If there is no concern about too much diaphragm suction due to pronounced airstream or anything else. Maybe i should try sketch a lever with proper feet angle in CAD and have them cut in Aisi316, and see how it does.

 

[rsingler]

My numbers were off. My estimated angular potential lever movement was estimated off the diagram I made of the lever mechanism.
When I actually look at the barrel itself, the maximum lever travel is only about half that much, because the limiting contact with the barrel is above the plane of the pivot.

So comparing 0-25° with 12-37° lever foot angle, the decrement in poppet travel due to the poorer foot geometry is only about 7%.

This is a nice theory discussion, but I'm not sure it's significant enough to warrant building a custom lever.

 

[luE]

Thank you for the correction.
I work as a product development engineer, manufacturing products primarily made of sheet metal. So the hassle for me to test out the theory is limited.