My better reactive trigger explanation and something to look for on your RT

[Spider-TW]

Secretweaponevan asked a different question the other day; "why does the RT have a reactive trigger?". Usually the question is "how can I get my RT to RT?", the answer to which is usually some combination of higher pressure, clean regulators and shorter on/off pins.

I had always assumed that it had to do with the RT effect, since the valve was named "RT" and the RT effect increases as you increase the input pressure. That worked out just like they say assumptions work. Being unable to connect the reactive trigger with the "RT effect", I had to start over with the movie on zdspb.com and the diagrams.

It looks to me that the "RT effect" as described in the RT chronograph procedure is just a side effect of the very fast charge of the regulator. I think Tom designed the reactive trigger first and found the "RT effect" as a result. I would be happy to hear if I am wrong or right.

The reactive trigger on the RT valve is the result of the jet of gas across the bottom side of the on/off pin. The velocity on the jet is high enough to create suction and entrainment of gas over the top of the pin and push down on it. This design is similar to an eductor, which uses a jet to provide suction on a stream perpendicular to the jet flow. Faucet attachments for draining water beds are similar.



For the time that the reg is recharging through the reg pin, the jet is pulling gas down. When the reg pin closes off, the jet stops and you are left with near normal pressure on the on/off pin which you should be less than what you would be applying if you try to take up the force on the pin from the pressure and the jet flow suction. The force on the pin from the jet varies directly with the velocity of the jet, which comes from the input pressure.
**^probably not^**

So besides keeping your reg clean so that the reg piston and reg pin can move fast, check that your RT on/off ports are lined up with your valve. I think this is why AGD started to use the square base on the RT on/off, to keep a pair the ports aligned with the reg pin. I've had a RT top that would come loose and rotate out of alignment. If that happened in an RT valve, it would greatly reduce the reactive trigger forces.

[secretweaponevan]

I think it is easier than that.

When you pull the trigger, regulated pressure (400 PSI or so) is acting on the small diameter of the RT on/off pin.

After you pull the trigger, unregulated pressure (input pressure) is acting on the larger diameter of the RT on/off pin top.

Since PSI is Pounds per Square Inch a larger diameter for pressure to act upon will result in greater force.

I was just curious as to why the RT effect dissipates a short while after a shot, and have it figured out as having to do with the cooling of the dump chamber and on/off bottom after a shot.

[Spider-TW]

I think it is easier than that.

When you pull the trigger, regulated pressure (400 PSI or so) is acting on the small diameter of the RT on/off pin.

After you pull the trigger, unregulated pressure (input pressure) is acting on the larger diameter of the RT on/off pin top.

Since PSI is Pounds per Square Inch a larger diameter for pressure to act upon will result in greater force.

I was just curious as to why the RT effect dissipates a short while after a shot, and have it figured out as having to do with the cooling of the dump chamber and on/off bottom after a shot.

If that were the end of it, then the RT on/off would be reactive in a classic valve, would it not?

[snoopay700]

If that were the end of it, then the RT on/off would be reactive in a classic valve, would it not?

If you have your velocity set high enough it does. The air flows in from the on/off top to both the dump chamber and the reg piston, so that's how it fills the dump chamber first, i think you're misunderstanding how it works.

That's why higher input pressure makes it more reactive, it hits the on/off top before it's even regulated, and that pushes down with more forces making it more reactive.

[Spider-TW]

If you have your velocity set high enough it does. I think it has more to do with the on/off, but the way that the RT works, the air flows in from the on/off top to both the dump chamber and the reg piston, so that's how it fills the dump chamber first, i think you're misunderstanding how it works.

I see that on the fill now, thanks. Only the reg piston discharge comes across the bottom of the pin top, which is too early and short to reset the trigger.

So the on/off pin top sees unregulated (bottle regulated) air while the regulator is discharged? That would be a lot simpler. That would explain your high velocity comment on the classic as well. And that's what secretweaponevan was trying to tell me.

So the RT kick starts out high and diminishes as the chamber fills. The chamber fill time sets the total rate of fire then; higher pressures make faster fills and higher rof.

Make sense to you?

I would still like to change the alignment on an RT top and see if it affects the fill time. I need a bps chrony though.

I know if I bat this around in circles long enough, I'll figure it out. :)

[snoopay700]

The one problem with your walkthrough of how it works is that the higher pressure yields higher rates of fire, it's more to do with the internal passages and how they are designed. With an 800 psi tank or a 2200psi output tank the highest rate of fire of the RT valve should be around 42 bps, although it may be higher than this because that figure is just calculated because the only solenoid that could activate the valve could only get it cycling at 26 bps, so it can cycle faster in theory than any electronic device can trigger it.

The higher pressure is so that there is a higher pressure pushing down on the on/off pin. Now that i think about it, under higher rates of fire what you've said in your first post could very well be what what causes the RT effect, and in fact that's probably why the top of the on/off pin is shaped that way. I actually think you're right on this one, and i just realized it while typing it up, because i was just looking at it on a shot by shot process, not under rapid fire. I think the two factors combine and the higher pressure on the RT top coupled with this creates even more force pushing your finger out (i realized you're probably right when trying to figure out how the pressure doubles pushing your finger out when the input pressure stays the same, it didn't make sense) which enhances the RT effect.

So in essence, you're right, just not in the initial way you were thinking i think, but that small amount of air rushing past the on/off pin from the regulator piston, since all of that air goes down the barrel (well most of it in real world situations) is what creates that additional 3 pounds of force or whatever, like for instance the 800 psi on the on/off pin is only 3 pounds, when you pull the trigger it is a 3 pound trigger pull, so it would make sense that it would push back out with 3 pounds since the pressure and the surface area of the on/off top stay constant. So for the trigger to push back with 6 pounds it needs that extra force from somewhere, and that is the air rushing past the bottom of the on/off top, which is why it only does it for an instance.

Long story short, you were right, but you were thinking of the process out of order i think. I probably wouldn't have realized this was going on if it weren't for this thread. Here's the animation that really helped me realize it too:

http://www.zdspb.com/media/tech/animations/rtemag2_6fps.gif

[Spider-TW]

It's definitely a dynamic, short term effect.

When the regulator is satisfied, there should be about 450 psi on both sides of the pin top, leaving just the shaft diameter to push against. After firing, the chamber is empty and the pin top gets 800 to 1000 psi. I was missing the high pressure on the top, as opposed to regulated 450 psi air like in a classic valve.

Like you say (I think) there may be three parts to the whole reactive trigger action; initial pull-down from the jet, static pressure until the on/off pops open, and downward flow on the pin to hold it open during recharge.

One thing I'm trying to get straight is the effect of adding input pressure to the rate of fire on my X-valve/max-flo setup. By adjusting the input pressure between about 800 psi and 900 psi, it will RT between about 13 bps and 19 bps. The flow rate of my remote air supply must top out about there as it doesn't seem to get any higher if I go above 900 psi.

Either way, it seems like a longer on/off pin gives you a little more finger travel to release. So if the whole thing were static pressure, a shorter pin would not get you much (seems like it would be easier to RT with a longer kickback). I like shorter pins in classic valves, but my x-valve RT setup is a stock .750 pin.

The shorter pin theory kind of derives from the ULT I think. Pin length was cockerpunk's question which started this whole thing.

[snoopay700]

It's definitely a dynamic, short term effect.

When the regulator is satisfied, there should be about 450 psi on both sides of the pin top, leaving just the shaft diameter to push against. After firing, the chamber is empty and the pin top gets 800 to 1000 psi. I was missing the high pressure on the top, as opposed to regulated 450 psi air like in a classic valve.

Like you say (I think) there may be three parts to the whole reactive trigger action; initial pull-down from the jet, static pressure until the on/off pops open, and downward flow on the pin to hold it open during recharge.

One thing I'm trying to get straight is the effect of adding input pressure to the rate of fire on my X-valve/max-flo setup. By adjusting the input pressure between about 800 psi and 900 psi, it will RT between about 13 bps and 19 bps. The flow rate of my remote air supply must top out about there as it doesn't seem to get any higher if I go above 900 psi.

Either way, it seems like a longer on/off pin gives you a little more finger travel to release. So if the whole thing were static pressure, a shorter pin would not get you much (seems like it would be easier to RT with a longer kickback). I like shorter pins in classic valves, but my x-valve RT setup is a stock .750 pin.

The shorter pin theory kind of derives from the ULT I think. Pin length was cockerpunk's question which started this whole thing.

Yeah that's pretty much what i was saying, although the pressure to keep the on/off open i consider to be the same pressure, so you can argue it's 2 steps, but it's the same thing.

The higher input pressure makes the trigger kick back out with more force than it usually would, and that makes it a lot easier to bounce off of your finger. That's pretty much the only thing higher pressure does.

As for a shorter on/off pin, i've noticed it in mine, and i think it's simply the pin has to travel less to trigger the gun, and shorter travel=higher ROF, especially when you're bouncing the trigger and it's all autonomous. Well no, not higher ROF, easier to attain that higher ROF i should say.

[athomas]

You guys are starting to understand.

When you pull the trigger on the retro valve, you are pushing against the regulated pressure that acts on the small diameter of the on-off pin. The air passage in the back of the on-off hole leading to the regulator is only pressure feedback to shut off the source pressure once the regulated chamber value is reached. Using a level 7 bolt the regulated chamber pressure is about 350 psi and combined with the sear force requires about 4 lbs of trigger force to move the on-off pin. Once the chamber empties, the lack of pressure feedback to the regulator opens the regulator and allows full bottle pressure (typically 800psi) to hit the larger top section of the on-off pin. The larger area of the pin combined with the higher pressure results in approximately 8lbs of trigger return force. A higher bottle output pressure would result in a higher trigger return force. This higher return force helps push your finger back as you release the trigger. Once the on-off pin opens the front chamber, it recharges back up to its regulated value so that the on-off return force is only the regulated value acting on the small section of the pin.

The reactive trigger (RT) effect is caused by this differential trigger force. If you pull the trigger with just enough force to move the sear and on-off pin, the higher return force exceeds this value once the bolt releases the chamber air. Since the return force exceeds the trigger pull force, the trigger bounces back to the ready position. At this point, the trigger pull force exceeds the regulated chamber force and the trigger pull force exceeds the force required to move the regulated pressure acting on the small area of the on-off pin again. The cycle continues as long as you can hold just enough force to exceed the regulated chamber force but not enough to exceed the unregulated return force.

The greater the differential between the regulated value and the input pressure, the wider the operating range that you can get the valve to go reactive. Since the chamber pressure is always constant, the only way to have a higher differential force is to raise the input pressure coming from the bottle regulator. The unregulated pressure acting on the top of the on-off pin is also only available at the start of the pin return. Once the on-off pin opens, the air never catches back up to the full unregulated force, plus the pressure is only acting on the small diameter of the chamber once the on-off area is open. So, its only the initial return reaction that is the full unregulated return force.

The length of the on-off pin affects the reactivity because it shortens how far the pin and trigger assembly has to travel. It is much easier to let your finger float a short distance than it is to float a longer distance. If the trigger pull is too long, you have to make a conscious effort to pull the trigger and it ruins the bounce because you cannot react fast enough to finish the trigger pull.

[athomas]

I meant to mention the AIR valve too.

The on-off pin is the same diameter all the way along its length. Since the air valve has no pressure feedback and only uses regulated air to push the top of the on-off pin, the maximum return force is exactly the same as the trigger pull force. This is approximately 4 lbs on a level 7 bolt using a 350psi chamber pressure. Thus, there is no reactive force in an AIR valve. Even if you install a retro on-off assembly, the differential force is too small to cause a noticable difference to allow reactivity.

AIR valve differential force is about 4-2 = 2 lbs with a retro valve on-off.

RT valve differential force is about 8 - 2 = 6lbs.

The retro valve has 3 times as much differential force and it is still hard to get it to go reactive. There is not a hope to get an AIR valve to go reactive.

[Spider-TW]

Athomas, I am a firm believer in the pressure differential between the normal regulated pressure and bottle pressure. However, I don't think that is the end of it.

There is something, probably the down flow on the on/off pin, that keeps the back pressure on the trigger while the regulator recharges. My trigger finger is not as consistent as my x-valve shoots. I find it difficult to RT at 13 to 14 bps because my finger is waiting on the trigger (could use a shorter pin :) ), as opposed to 19 bps where my finger just rides the bounce.

I've also noticed that with poor flowing bottle regulator on a remote hose set at over 900 psi, I can't get a good follow-up shot when I should have plenty of high pressure air in the hose (maybe it's just the RT effect on my only reactive pull). I know good flow from the bottle means sustained pressure on the on/off top, but I also know that my finger is not setting the cycle rate.

You might recall some. I searched the whole forum for "Tom-posts" on reactive triggers and all I found are discussions of tournament rules. Have you seen any?

[athomas]

Athomas, I am a firm believer in the pressure differential between the normal regulated pressure and bottle pressure. However, I don't think that is the end of it.

There is something, probably the down flow on the on/off pin, that keeps the back pressure on the trigger while the regulator recharges. My trigger finger is not as consistent as my x-valve shoots. I find it difficult to RT at 13 to 14 bps because my finger is waiting on the trigger (could use a shorter pin :) ), as opposed to 19 bps where my finger just rides the bounce.

I've also noticed that with poor flowing bottle regulator on a remote hose set at over 900 psi, I can't get a good follow-up shot when I should have plenty of high pressure air in the hose (maybe it's just the RT effect on my only reactive pull). I know good flow from the bottle means sustained pressure on the on/off top, but I also know that my finger is not setting the cycle rate.

You might recall some. I searched the whole forum for "Tom-posts" on reactive triggers and all I found are discussions of tournament rules. Have you seen any?

A good flow via the tank regulator allows the pressure on the top of the on-off pin to be higher for a longer period of time rather than just starting at the tank pressure and then barely keeping up once the pin opens the chamber. As long as the chamber is not full, the return force on the top of the pin will be larger than the original regulated pull force, because the air pressure from the bottle is pushing the top of the pin. The force is never as high as the initial impulse, but it is higher than the regulated trigger force.

It is sometimes very hard to find that sweet spot. What comes into play that is often ignored is friction of the pin and sear as well as the momentum of the movement from the initial impulse. The sear friction (where it holds the bolt) would affect the trigger pull but not necessarily the return. Another factor is the cycle speed of the bolt. The level 10 has a slower cycle speed than the level 7. If the level 10 is also a bit slower due to sticking or if it is tuned to a more softer setting, that too could affect to overall reactivity being that the sear holds the on-off pin up. It may not directly affect the reactiveness but it could slow down the rate of reactive firing.

I know there are some good posts from the past on reactive triggers. I haven't seen them in ages though. They were probably 5 years ago or more.

[Spider-TW]

I know there are some good posts from the past on reactive triggers. I haven't seen them in ages though. They were probably 5 years ago or more.

I found some RT threads from 2002 I think, but no good trigger posts.

How about the RT on/off top alignment bit? It seems that the holes on the top need to line up with the reg pin and dump chamber ports to get good flow (call it less back pressure if you like). The square base normally keeps these aligned, but if you take the top off to change the orings or put in some shims, it can turn out of alignment. You think that's worth an RT experiment? I wonder if it may have to do with some of the RT valves that refuse to RT, even though the bottle reg will RT a different valve.

[athomas]

The cut around the outside of the top has more capacity than the edge of the on-off pin. It really doesn't make any difference what the orientation is. Its always been the top of the pin that has been the greatest restriction in the air flow.

[snoopay700]

You guys are starting to understand.

When you pull the trigger on the retro valve, you are pushing against the regulated pressure that acts on the small diameter of the on-off pin. The air passage in the back of the on-off hole leading to the regulator is only pressure feedback to shut off the source pressure once the regulated chamber value is reached. Using a level 7 bolt the regulated chamber pressure is about 350 psi and combined with the sear force requires about 4 lbs of trigger force to move the on-off pin. Once the chamber empties, the lack of pressure feedback to the regulator opens the regulator and allows full bottle pressure (typically 800psi) to hit the larger top section of the on-off pin. The larger area of the pin combined with the higher pressure results in approximately 8lbs of trigger return force. A higher bottle output pressure would result in a higher trigger return force. This higher return force helps push your finger back as you release the trigger. Once the on-off pin opens the front chamber, it recharges back up to its regulated value so that the on-off return force is only the regulated value acting on the small section of the pin.

The reactive trigger (RT) effect is caused by this differential trigger force. If you pull the trigger with just enough force to move the sear and on-off pin, the higher return force exceeds this value once the bolt releases the chamber air. Since the return force exceeds the trigger pull force, the trigger bounces back to the ready position. At this point, the trigger pull force exceeds the regulated chamber force and the trigger pull force exceeds the force required to move the regulated pressure acting on the small area of the on-off pin again. The cycle continues as long as you can hold just enough force to exceed the regulated chamber force but not enough to exceed the unregulated return force.

The greater the differential between the regulated value and the input pressure, the wider the operating range that you can get the valve to go reactive. Since the chamber pressure is always constant, the only way to have a higher differential force is to raise the input pressure coming from the bottle regulator. The unregulated pressure acting on the top of the on-off pin is also only available at the start of the pin return. Once the on-off pin opens, the air never catches back up to the full unregulated force, plus the pressure is only acting on the small diameter of the chamber once the on-off area is open. So, its only the initial return reaction that is the full unregulated return force.

The length of the on-off pin affects the reactivity because it shortens how far the pin and trigger assembly has to travel. It is much easier to let your finger float a short distance than it is to float a longer distance. If the trigger pull is too long, you have to make a conscious effort to pull the trigger and it ruins the bounce because you cannot react fast enough to finish the trigger pull.

Ah damn we were close lol, i mainly said he was right because there would logically be air moving past the bottom of the on/off top, but i started over thinking the whole process and didn't think about the differential pressures at all. I mean i'm sure the air rushing past has some effect, but (and i was thinking this too but it was the only thing i could think of at the time because i was focused on it so it was the only explanation i had) the effect would be fairly small.

As for the on/off pin length that was the gist of what i was trying to get across.

Actually now that i think about it, what you said isn't completely right, because when the gun is at rest the on/off is open, and so the air above the on/off is regulated to the same pressure as in the dump chamber (lets say 350). So you are pulling against the 350, there is no pressure difference helping you (the on/off would have to be closed for this to happen). Then when the gun finally fires the regulator has no pressure on it and so it opens up the cut off and lets the 800 psi on top of the on/off pin, higher pressure yields more force, but the trigger pull would still be the same weight, which is why people don't notice an increase in trigger pull strength with more pressure, if there was a pressure difference like you say they would.

As for the air valve the reason that isn't reactive is because the air is regulated before it hits the on/off, so it will push out with around the same that it is to pull, although if your velocity is way too high then it will kick out with more pressure which causes this. The on/off being used has nothing to do with the RT effect, although the air rushing past may play a small part.

Also the on/off top is not restrictive to flow when the trigger is pulled.

And as for the differential pressures, the way the on/off top is shaped probably lightens teh trigger pull from the classic, but that's also why it lightens it in the classic, so there is no differential pressure per se, but the added area on the bottom makes the overall trigger pull lighter.