Tuning FX Impact Mk2/M3 - reducing valve opening effort

[Seeker]

Hi,

We know that FX Impact has a kind of a balanced valve and I think we can reduce the effort needed to open that valve a little bit. Just have a look:

The pressure acts against the surface marked in red. Why not changing its profile so that only a part of the pressure acts along the rod axis?

What do you think about that?

Thanks!

 

[MikeVV]

Interesting puzzle.

Years ago, (I worked in the Aerospace Industry) we had to fill a void with epoxy to lock three legs together after a satellite dish was aligned (three places). Well, the "void" where the three legs were, was very small, and the epoxy was somewhat thick, thus, it was a difficult squeeze !

I was tasked with finding if an "angle", or a radius was better than a 90° squared off corner was where the epoxy had to pass.

LONG story short, a "radius" was..."marginally" better than a standard 90°, and no other angles changed the pressure required to force the epoxy into the void.
I doubt that "air" would be much different, especially when you look at the coefficient of drag on cars for the effect of air passing over the front of the car, dealing with streamlining. Which is basically the same situation you are talking about. The only way to reduce that drag is to make the car smaller, that is, narrower and or shorter (ground to the top).
So, in your situation, would be to make the larger diameter pin smaller, which...you can't do !
Your comment about "part of the pressure" is incorrect thinking. You aren't lessening the surface area, you are "only" moving into a different location.

Properly quantifying any improvements in your situation, would be a difficult, expensive task at best.

BUT...go for it, I'm never...one to stop someone from his (her) experimenting.

Mike

 

[mubhaur]

Hi,

We know that FX Impact has a kind of a balanced valve and I think we can reduce the effort needed to open that valve a little bit. Just have a look:

View attachment 283663

View attachment 283664
The pressure acts against the surface marked in red. Why not changing its profile so that only a part of the pressure acts along the rod axis?

View attachment 283666

What do you think about that?

Thanks!

View attachment 283665

It might work.

 

[Seeker]

Interesting puzzle.

Years ago, (I worked in the Aerospace Industry) we had to fill a void with epoxy to lock three legs together after a satellite dish was aligned (three places). Well, the "void" where the three legs were, was very small, and the epoxy was somewhat thick, thus, it was a difficult squeeze !

I was tasked with finding if an "angle", or a radius was better than a 90° squared off corner was where the epoxy had to pass.

LONG story short, a "radius" was..."marginally" better than a standard 90°, and no other angles changed the pressure required to force the epoxy into the void.
I doubt that "air" would be much different, especially when you look at the coefficient of drag on cars for the effect of air passing over the front of the car, dealing with streamlining. Which is basically the same situation you are talking about. The only way to reduce that drag is to make the car smaller, that is, narrower and or shorter (ground to the top).
So, in your situation, would be to make the larger diameter pin smaller, which...you can't do !
Your comment about "part of the pressure" is incorrect thinking. You aren't lessening the surface area, you are "only" moving into a different location.

Properly quantifying any improvements in your situation, would be a difficult, expensive task at best.

BUT...go for it, I'm never...one to stop someone from his (her) experimenting.

Mike

Sorry, I was not precise enough. Pressure works in all directions and it generates the force perpendicular to the surface. When the shape is like in the original part the power vector is all in axis with the rod and it pushes delrin poppet against the valve wall. When we make an adjustment which I proposed then the force vector is changed and only one vector component is in axis with the rod, hence delrin poppet is not pushed that hard.

It does not rely on aerodynamics. It just modifies the force vectors.

 

[Seeker]

It might work.

If I know physics at least a tiny but then it must work. Question is about force reduction but it can be calculated. If the angle is 45* then only 50% of the force pushes against the poppet. When the face is square like in the original part then 100% of force pushes the poppet. If we have 150 bars in our plenum then 150kg od force is applied to any 1cm2 of the surface.

 

[bigHUN]

Assuming you have a lot of room around that area marked up on the bushing, if you would put a "chamfer" won't help much and won't hurt neither, different story if there would be a tight space around...
If you have a concern to make that Valve Rod move faster, you shall polish to a mirror finish the portion of the 3mm rod that is sliding on the 2 orings (in the Plenum End Cap).

 

[Chuck-in-Ohio]

Work the math for the 2 different surface areas, flat vs 45° and see if the pressure exerted on the seat changes.
1/2 the force working over a larger surface area may not gain you a reduction in force exerted on the valve seat.

 

[Seeker]

True. But if something can be improved just a little with minimal cost - why not doing it? We can apply more gradual chamfer as 45* is pretty steep - then we can achieve e.g. 30% of the original force or even less. I like to be one step ahead of FX which is ... actually pretty easy for me.

Just check how the poppet itself looked like previously:

I think they figured it out and they changed the delrin part to be conical to reduce the force by changing its vectors.

Guys, I am not sure if you get what I mean by the proposed mod. Just keep in mind that it's kind of a balanced valve. More on them here: https://hardairmagazine.com/ham-columns/balanced-valves-for-pcp-airguns-theyre-here-today/

 

[xyon]

It will not make any difference at all. The Magnitude of the force acting parallel to the rod will be identical. You will see that it you draw your force vectors to scale.

 

[Airgunmann]

Well that kind of a balance valve works fairly well I would say using only like 14 grams of a hammer other guns without any sort of balance valve use 60 plus grams I had like a 109 grams in my air force for a hammer but yeah I'd say do it it can't hurt any

 

[Seeker]

Original hammer is about 18.3g plus about 6g(?) of a hammer weight.

 

[Airgunmann]

Going to peek over a derlin seat will make the opening force a little easier because peek doesn't flex like derlin and you can also make the poppet smaller because of the stronger peek material I have a impact but haven't had it apart to see how much smaller you could make the poppet seal

 

[MikeVV]

Sorry, I was not precise enough. Pressure works in all directions and it generates the force perpendicular to the surface. When the shape is like in the original part the power vector is all in axis with the rod and it pushes delrin poppet against the valve wall. When we make an adjustment which I proposed then the force vector is changed and only one vector component is in axis with the rod, hence delrin poppet is not pushed that hard.

It does not rely on aerodynamics. It just modifies the force vectors.

Actually...it's the SAME actions !

Plus...did you read the experiment that I did at work...again, the same...thing !!

And actually I did make a misstatement. The angle that you put on the valve, ACTUALLY increases, the surface area and since any load put on that angled area, will be a 90° vector, or pushing in two directions ! So in regality you will be increasing...the load requirement to move the valve.
EXACTLY the same as my epoxy testing AND YES...aerodynamics.

Got a Machinery Handbook...LOOK it up ! Or most and design hand book, I'd assume may answer your question.

Mike

 

[nervoustrig]

It will not make any difference at all. The Magnitude of the force acting parallel to the rod will be identical. You will see that it you draw your force vectors to scale.

^ correct answer.

 

[Seeker]

Guys, just to keep things as simple as possible - let's take a look at a traditional valve we all know.

Do you still think there is no difference at all how strong the poppet is pushed against the cylinder wall? If so the we must know different physics.

 

[nervoustrig]

Yes, the normal force holding it closed is the same. Therefore the hammer energy soaked up to knock it open is the same in both scenarios.

It is true however there will be some increase in dwell for the tapered/shaped poppet head on account of less of a sail effect attempting to slam it closed.

 

[Seeker]

How do you know if the force is the same? Force vectors are different.

 

[nervoustrig]

The proof would take more time and effort to diagram out than I have time to devote right now, but suffice it to say this is well-trodden ground that has come up from time to time over the years by tuners and tinkerers looking for ways to make valves easier to knock open, particularly big bores...without the complexity and expense of a balanced valve, and/or to preserve the ease of tuning for a useful bell curve.

 

[heavy-impact]

What we need is less shrouding of the valve and a more pressure neutral shape for the poppet in airflow. Shape A is far better than shape B.
Once you knock it open A has far less drag than B as far as airflow trying to push the poppet back down. Laminar flow across the poppet would be ideal if it were achievable. The load on the poppet is static until you open it and airflow makes the load dynamic.

I like to be corrected so if I'm wrong please educate me and I'll thank you.

 

[Seeker]

The proof would take more time and effort to diagram out than I have time to devote right now, but suffice it to say this is well-trodden ground that has come up from time to time over the years by tuners and tinkerers looking for ways to make valves easier to knock open, particularly big bores...without the complexity and expense of a balanced valve, and/or to preserve the ease of tuning for a useful bell curve.

It should not be difficult to create computer simulation using FEM in e.g. Adina software.