Alex, your reiteration of my statements is 100% correct.... What happens on the plateau is that once you reach it, releasing more air by using more preload is only blowing air out the muzzle after Elvis has left the building.... As you reduce the preload below the start of the plateau, you are closing the valve while the pellet is still in the barrel.... For most PCPs, closing the valve when the pellet is halfway down the barrel saves about half the air but only loses about 3% of the velocity.... Obviously, this is MUCH more efficient than operating on the plateau.... If in your example (plateau at 900 fps) you really needed to shoot at, say 950 fps, you would need to increase the regulator setpoint pressure enough to move the plateau up to at least 980 fps, find the preload required to reach that, and then detune 3% back to 950 fps.... You can get a pretty good idea of how much you would need to increase the pressure by calculating the difference in the plateau velocities, and then squaring that (to get the FPE), as follows....980 / 900 = 1.0889 (ie nearly a 9% increase in velocity)…. That represents an increase in energy of (1.0889 x 1.0889) = 1.186 times.... Therefore, you would need to increase the setpoint pressure of the regulator by that same amount.... If your setpoint was 1200 psi when the plateau was 900 fps.... you would try a setpoint pressure of (1200 x 1.186) = 1423 psi.... So, if you increased the regulator setpoint to 1400-1500 psi you should be able to find an efficient tune at about 950 fps when you tune to 3-5% below the (now higher) plateau….If you refer back to the graph in Reply #91 on the previous page, you can see what happens to the velocity curve as you reduce the preload.... Note what happens if you drop the velocity 10% or more below the plateau.... Below the setpoint, the gun shoots like an unregulated PCP (because it is, the regulator is wide open)….Bob
I have seen it done with a high pressure "T" fitting.... Other than making a whole new front end with gauge and fill ports I don't know of another way....Bob
With time comes increased clarity and understanding (ie I'm always learning).... so I thought I would revisit this subject to add a chart that might help you understand what happens as you tune a regulated PCP with progressively less velocity than the plateau.... Here is an updated version of the chart in the first post of this thread....The 3%, 5% and 10% below Plateau velocities are approximate only, but will give you an idea of what happens as you reduce the hammer strike, and hence the velocity, on a regulated PCP.... It will show you exactly why I like to tune 3-5% below that plateau.... because (at about 5% down) you get a few more usable shots below the setpoint before the velocity drops off.... or at the very least (at about 3% down) you save a lot of air compared to tuning up on the plateau, with very little loss of power.... The chart also shows what happens if you tune about 10% (or more) below the plateau.... Note that below the setpoint the velocity increases significantly.... and while operating in that realm gives you extremely good efficiency, for some applications (eg. Field Target, or in some countries where there is an FPE or velocity limit) that bump could put you over the limit.... Every gun is a bit different, and yours might produce a curve like the "5%" one above only 3% below the plateau, or it might be 7% below.... but to date those would be about the outside limits I have found to produce a tune that has a usable shot string (ie within a ~1% ES) extending slightly below the setpoint, which is the tune I prefer.... I hope this chart allows you to visualize what I have tried to confer in this thread....Bob