I have been reading a lot of info in the forums about consistency, velocity, stabilizers, FVA mods, powertubes, and RVAs. As soon as I thought I knew what I was gonna do (palmer stab, gold pt, and RVA w/madman spring) I caught two curve balls.
1. Invictus - Glenn Palmer actually suggests that the front velocity screw be backed out as far as possible without it being removed (in otherwords until its flush inside the power tube). Then adjust the regulator until you chrono a FPS of around 300. From there, then use the front velocity screw to "fine" tune your FPS to 285 or less. I'm sure this same procedure would work if you have the rear velocity adjust instead.
2. and then I came across an exchange between The Spiritus Raptor and Scoreshot basically saying the FVA mod is a myth and using it will help your consistency, but scoreshot runs an RVA w/stock spring.
I guess my questions are if you use the FVA, then why a RVA too? I don’t mean to call anyone out here, from what I’ve read here so far, you all are very knowledgable and well respected here on the forum, I am just trying to learn/understand. thanks

I would say more adjustment options.

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so an RVA is not going to help w/ shot-to-shot consistency, it is just another adjustment to play with?

Well, let's examine the manner in which they work.

The FVA is basically a set screw which protrudes into the power tube. It disrupts the airflow towards the ball, producing turbulence which prevents some of the air imparting full force on the ball. The more it is screwed in, the more the airflow is disrupted, and the slower the ball travels.

Turbulence, however, is not a very consistent method of controlling velocity. Gas rushing through a tube is not always predictable, and the effects of induced turbulence are never consistent. The FVA, thus, is a crude but acceptable way of controlling velocity.

An RVA, by contrast, works by changing the tension on the drive spring which powers the striker. Adjusting it inward increases the tension on the spring. With increased tension, there is more force on the hammer as it moves to open the valve, thus the valve pin is held open for longer (because the blowback is slower to push the hammer back). As the valve is open for longer, it allows more air through the valve and into the power tube. With more air, the ball is able to accelerate more, and thus more kinetic energy is transferred to it, resulting in higher velocity. Decreasing the tension on the spring has the opposite effect. This is the same principle that a spring kit is based on.

Ideally with a RVA one should also have a Gold power tube, so that the FVA does not impart any turbulence on the airflow. It is this lack of turbulence associated with the lack of a FVA - and not merely the presence of an RVA - which results in consistency.

However.

Using a gold power tube without having an RVA is folly, as then there would be no way for you to adjust your velocity. Since the RVA imparts no turbulence on the air flow, all of it (as much as possible) is reaching the ball without restriction, and the ball will most likely fire hot. Thus an RVA must be used with a Gold tube to control velocity by changing the striker tension.

Ideally one would also use a regulator (incidentally, the combination of Gold tube, RVA and regulator offers the best shot consistency for an A5 setup) so as to be able to control air pressure and thus efficiency.

Fin.

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Not necessarily true and you do allude to this in the next paragraph. You could use a reg to control the input pressure and therefore adjust the velocity by raising or lowering the pressure. This is how a lot of electros (such as ones with spool valves) work. Adding an RVA to this mix would give you more fine tune control since that would in essence allow you to adjust the dwell on the valve.

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There are no wrong or dumb questions. I run an FVA/RVA combo on my A5 and I have a distinct need for doing so. To go along with what has already been said about how the FVA controls velocity, it does one other thing. The FVA creates backpressure by restricting (or should I say constricting) the flow of air thru the power tube. The A5 uses backpressure to run the various pneumatic accessories on the marker: the cyclone and the RT. I have an RT and this is where my distinct need comes into play. The more backpressure I have, the greater the sweet spot on the RT. Consequently, I keep the FVA half in and use the RVA to adjust velocity.

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ahhhhhhhh yes, the fog has lifted. one more question. those using a gold pt or FVA mod, are they running at a higher input pressure in order to operate the cyclone, versus another setup using a set FVA setting, a stab to due the major velocity tuning, and using the RVA to fine tune. i would guess so, yes?

Well...since the stock A-5 has no pressure control, it operates at the output pressure of the tank...which needs to be a high pressure tank in order for the A-5 to recock itself. (Unless you have low pressure kit installed on the A-5 of course.) It doesn't matter if you are shooting 150 fps or 300 fps (assuming a full tank)...you use exactly the same pressure. This is what a reg brings to the party...pressure control.

edit: spelling

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got it now. thanks for the time and help

I also run a FVA and RVA as my standard setup. I totally agree with regard to the FVA increasing back pressure and consequently, in many cases, improves cyclone/RT performance by forcing increased air flow to those "pneumatic accessories". However, the a5 does not use back pressure to run the cyclone and rt. Those accessories run without any added back pressure from the FVA. They are feed directly from the main air valve with the same forword pressure air charge that feeds the power tube. Actually, the cyclone/rt feed port is located just before the right hand air channel in the valve body. The FVA provides back pressure in the air channel which forces more of the initial air charge from the valve to the cyclone/rt feed port. So, although the cyclone and rt are not run by back pressure, the back pressure from the FVA forces more of the initial air charge from the valve to those accessories, in some cases improving their performance. No disrespect intended Hwyman. I'm sure you are very knowledgeable. Just thought a clarification would be in all our best interests.

Respectfully,
Scoreshot

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