Tuning A valve/regulator question…

[Marcdeo]

Hi guys. I’ll get right to it… I’m interested in learning the ins and outs of PCP mechanics (as best I can) as I will be upgrading to an M3. Basically what I want to do is explain things as I understand it, and really just looking for someone to tell me “yes, you’re correct” or “no, you got this wrong”. This is weird perhaps but it’s how I learn. I appreciate anyone willing to take the time. Thank you.

so the cylinder pressure enters the regulator though the hollow piston. As pressure rises in the regulator it pushes against the piston spring until the knife edge of the piston meets with the soft nylon portion of the adjustment screw, sealing off the regulator from the cylinder. Move the adjustment screw closer to the piston and LESS pressure is required to close the gap and seal it off. Move the adjustment screw further from the piston and more pressure is required to cross the distance seal it off. So for higher reg pressures we increase the space between the piston and adjustment screw. For lower reg pressure we decrease this space.

The valve adjustment (on the M3 for example) closes the valve after it’s been struck by the hammer. THEORETICALLY, if we cranked this valve return spring to max tension, could it cut off air supply to the transfer port before the regulator has had an opportunity to dump its load (bazinga, lol), which would reduce pellet speed?

Am I on the right track? 


thank you all very much for your time…

 

[nervoustrig]

Your description of the regulator gap is correct.

On the second part regarding the valve spring tension, it provides some limited means to tweak valve lift and dwell (how far it opens and how long it stays open, respectively). The valve will never dump the entire charge from the regulator, else efficiency would be atrocious. So the valve spring does not manipulate lift and dwell that coarsely, think of it more as a fine adjustment.

 

[Marcdeo]

Thanks. I was more “taking it to extremes” to see if my direction was correct, if that makes sense. But I understand what you’re saying. So if my dwell time was “too long”, could there be potential air turbulence behind the pellet (not sure if that would even effect flight) causing instability? Or could there be wasted air? In other words, would tightening (reducing) up the dwell time improve accuracy or perhaps increase efficiency by reducing wasted air? What’s the real benefit to fine tuning this aspect?

also I’ve heard that you should take the valve adjustment screw right to the point where power drops, and then back it off a bit. My understanding is that tightening up this screw too much (too little Dwell time) would cut off the regulator pressure before it has a chance to fully dump and get the pellet up to speed. Am I on the right track? 

 

[nervoustrig]

In other words, would tightening (reducing) up the dwell time improve accuracy or perhaps increase efficiency by reducing wasted air?

Generally speaking, yes. It's no good for accuracy or efficiency to be blowing a large volume of air from the end of the barrel after the projectile has left the muzzle. However the first step is not the valve spring, it's the hammer spring. That's the coarse adjustment. Usually a regulated PCP will operate very nicely when the hammer spring tension is set to deliver between 95 - 97% of peak velocity. When at this state of tune, it will have both good efficiency and good consistency (low extreme spread).

Then experiment with the valve spring tension to fine tune to see if it helps tighten up your groups or the extreme spread or both.