retro reg question

[xatle]

so, we all are aware of the velocity differance between rates of fire with retro/rt/emag valvs. this is due to the air heating up when it fills the dump chamber and the small drop in pressure when it cools down, causing a cold shot at the beginning of a fast string.

so heres my question, when the air cools down and the pressure drops, why doesnt the reg notice the drop and let in more air to compensate? i am hoping someone will clarify for me how this reg works.

[FrAuStY]

It seems to me that (maybe I'm looking at it wrong just makes sense) That you would chrono it at the hottest point.. (when air is heated, not cooled) by keeping the on/off closed.. the air is not flowing. Then when you open the on/off, the incoming air gets heated when filling chamber. If you left the trigger out.. that would cool down and shoot at your lowest velocity.
Now when you chrono it.. you close the on/off, then when you let off it,the air comes in and heats up you would want to shoot the gun right then. Your velocity will go up from the previous one due to the temp change. You would adjust your velocity from there and repeat. The idea is to always shoot the gun when the air is hottest. That way.. if you get flagged for velocity overage you will never be shooting hot. And under rapid fire when the guns recharging and staying hot it will always be shooting consistently at your chrono'd speed. Make sense? To me it has nothing to do with the reg needing to fill 20psi difference. You don't shoot your gun cold.. you shoot it when its hot. The RT was brought out for rapid fire not your one or two shot gun. :)

[xatle]

yes, but what is it about the reg that prevents it from trickleing in a little air to compensate for loss of pressure due to cooling? does the valve sort of snap fully open when the pressure gets low enough, and then when it gets high enough it snaps fully shut again, with no inbetween? does it just not close fast enough so it sort of overpressures itself, then when it cools the pressure drops to where the reg wanted it to be in the first place? does the expansion from heat buildup happen after the valve has closed causing a momentary spike in pressure whereafter the air cools and drops the pressure back to the point it was at when the valve closed?

anybody know how this works? i dont have one or i would break it down and poke at things till i understood it.

[Halliday]

Here's another question:
What is speed difference between a "cold" and "hot" reg? Say you do the regular chrony procedure, getting a "hot" reg and dialing say 280fps. What shot will a "cold" shot be at? 270fps? 260fps? What's the speed difference, aprrox?

[pbguy888]

Originally posted by Halliday
Here's another question:
What is speed difference between a "cold" and "hot" reg? Say you do the regular chrony procedure, getting a "hot" reg and dialing say 280fps. What shot will a "cold" shot be at? 270fps? 260fps? What's the speed difference, aprrox?

OK im pretty sure this is what your askin.

280 fps = 190 mph
270 fps = 184 mph
260 fps = 177 mph

[Halliday]

MPH? Nope. If an RT/Retro is chronyed at 280fps for a burst, what fps is it at for a single shot?

[anthraxxx]

OK resurecting the question on this thread. the retro valve has velocity differences between rapid and slow fire. has anyone measured the difference over a chrony? even eye ball it? i have noticed the first shot in a string dipping and then the ones that follow holding true. any comments on this guys?

[xen_100]

technically, if you had a long string of shots that heated the air and then stopped. the reg would compensate for the air cooling by letting in more air. so you should not see a very big difference at the Chrony.

[grumpyoldman]

Maybe this will shed some light in the original question. The reason the regulator doesn't open up after the air charge cools is because of friction. It takes a certain amount of pressure drop to make the piston in the reg move. Lets say 100 pounds (about what my raptor rex needs) is needed to cause the reg to cycle, since the change in pressure due to temp drop is probably alot less then this, the reg stays closed. Someone with some more info can narrow down the numbers if you really need more info.

Clear as mud?

Grumps:cool:

[athomas]

Its like grumpyoldman said.

The regulator needs a certain amount of pressure differential in order to operate properly. A minimal chamge in psi that could cause a slight velocity drop would not have enough pressure differential to cause the regulator to allow more air into the front chamber.