68 Classic Valve Question - What realistic FPS consistency should one expect?

[Mr. Red]

I'm a little new to the world of mags, and was curious what realistic fps consistency one should be expecting to get out of the default setup: 68 Classic Valve + LVL 7 bolt.

I know there are a several of factors that come into play (gas source, input pressures, paint to barrel match, gun maintenance, etc.), but when everything is setup as correctly as one can achieve in paintball, what have you observed during your user experience with the 68 classic valve?

[BTAutoMag]

its all dependent, as you said on several factors. on my 68 I get +-6

[OPBN]

Just really depends on paint. I have had days where aside from the hotter first shot I am within +/- 3fps. Other days, I have seen fluctuations of up to 10 FPS.

[dboggs79]

Shot 10 rounds through my pump a week or two ago. 279-283
That probably won't ever happen again. It is usually +/- 4 or 5 though.

[Syko89]

Does lvl 10 decrease efficiency?

[dboggs79]

No. Decreases it if anything.

[Nobody]

Does lvl 10 decrease efficiency?

yes. you are using more air pushing on a greater surface area of the bolt. then if you do engage the L10, you are using a "shot's worth" of air when you don't chop a ball.

now, you can play around with the L10 and an adjustable reg, and you can lessen the decrease. on my classic, i don't know what i did, but somehow i actually increased the shot count. i don't know what deal with the devil i made, or a f***ed up and got it right, so my results will differ from yours.

[Mr. Red]

Very cool. Thanks guys for sharing your findings. Currently it's at +-15fps, but visible inspection indicates it has a slightly less than perfect reg seat. The reg seat will be getting replaced as soon as possible with a new one when it arrives in the mail. I was just seeing on what to really expect, and not to get discouraged if it wasn't shooting in the -+3 range.

Also, does anyone know what the input/output pressure ratio the AGD AIR REG was designed with? Such as if had a 30:1 ratio, where if the input pressure spiked 30psi, then the output would only go up 1psi.

[athomas]

Very cool. Thanks guys for sharing your findings. Currently it's at +-15fps, but visible inspection indicates it has a slightly less than perfect reg seat. The reg seat will be getting replaced as soon as possible with a new one when it arrives in the mail. I was just seeing on what to really expect, and not to get discouraged if it wasn't shooting in the -+3 range.

Also, does anyone know what the input/output pressure ratio the AGD AIR REG was designed with? Such as if had a 30:1 ratio, where if the input pressure spiked 30psi, then the output would only go up 1psi.

The reg seat will definitely cause inconsistency. The consistency of the paint is the biggest factor in velocity consistency if the valve is working properly. Other items are really just factors in rates of fire or efficiency.

The ratio of change isn't going to be a big factor. The tank regulator output does lower as the tank empties from 4500 psi to 800 psi. The change depends on the regulator used on the tank. Being that the output might change by 50 psi (extreme case) from full to empty, the AIR valve might change by 5 psi (worst case at 10:1). Since the operating pressure in the chamber is over 350 psi in a level 7, a 5 psi change would only be a 1.5% change in pressure which would impart less than a 1.5% change in velocity at the upper end of the operating velocity range. At 1.5% change thats only 4 fps. So, looking at those numbers, any change in velocity would be less than 4fps for any spike in pressure around 50psi. The numbers I used are not truly accurate AGD numbers. I really don't know the AIR valve ratio, but I suspect it is actually much greater than the ratio I used for explanation purposes, so the numbers should be better than my worst case scenario.

[Mr. Red]

Hello. Thank you for the figures athomas (numbers are always fun to play with), but by chance does anyone on AO actually know if the 68 CLASSIC AGD AIR REG had it's pressure ratio released to the public? I also assume it would be higher/better than 10:1 since it was built in a time when everything ran on C02 (a gas source that is more prone to pressure spikes), and it was largely being run on straight C02 (remote coil/anti-siphon tubes/expansion chambers tech) with success. Then again, if it was never released, it might as low or worse than 10:1.

[athomas]

Hello. Thank you for the figures athomas (numbers are always fun to play with), but by chance does anyone on AO actually know if the 68 CLASSIC AGD AIR REG had it's pressure ratio released to the public? I also assume it would be higher/better than 10:1 since it was built in a time when everything ran on C02 (a gas source that is more prone to pressure spikes), and it was largely being run on straight C02 (remote coil/anti-siphon tubes/expansion chambers tech) with success. Then again, if it was never released, it might as low or worse than 10:1.

If someone had an accurate pressure measuring device, it could be easily measured. Make an adapter to screw into the front of the bolt stem. Accurately measure the input pressure at a high value and then apply it to the valve input and measure the pressure in the chamber. Change the input pressure to a low value and do it again, measuring the chamber pressure. The change in input divided by the change in chamber pressure would be the ratio.

[Spider-TW]

I think you're looking at the area of the reg pin seal versus the piston diameter. I don't recall those offhand, but if the pin is about 1/8" in diameter and the piston is 1/2" in diameter, the ratio is 16:1. The ratio on the RT reg is much higher (~100:1). With a good HPA bottle reg on a classic, paint variations are much larger than the reg variations.

[Mr. Red]

Thanks Spider-TW.

I called AGD today, concerning the input/output ratio, and was told "they didn't know. It's a regulator; it just regulates." Gotta love tech support.

[athomas]

The input pressure pushes on the small diameter of the regulator valve pin while the chamber pressure pushes back. The valve pin is not fully sealing the hole in the regulator seat oring, so air flows past and not all force is applied to the cross section of the pin until the pin actually closes. At this time, the input pressure actually applies pressure to the larger diameter section of the valve pin, but that is not so important while the chamber is filling and being regulated. Only the chamber pressure pushes out on the larger regulator piston assembly. So, as the regulator reaches its final regulated pressure, the force pushing out on the regulator piston assembly is the primary air force doing the work. A change in the input pressure won't have a large effect on the regulated air pressure in a system like this. If anything, the differential pressure between input and chamber may cause the valve pin to close a tiny bit quicker as the regulator reaches its final pressure value due to the larger end of the pin being acted on by more input force. the differential value would be small compared to the chamber pressure on the large regulator piston assembly anyway, so it would be inconsequential. The pressure of 350 psi acting outward on the larger piston would be about 69lbs. The differential force on the small section of the pin would cause a difference of 0.012 lb per psi of pressure change. So, a change of 50psi would cause 0.6 lb of force change which would result in just below 1% change in regulated pressure or 3.5psi which equates to about 15 to 1 ratio, which coincides with the numbers that Spider-TW indicated. The pressure value will go up as the input pressures go down, which is opposite to what most people would expect.

[Mr. Red]

Very cool. Well that's definitely more helpful than tech support. LOL.

So something close to 15:1 or 16:1. Much better than the 10:1 figure previously mentioned. Thanks.