After writing the previous two posts, I went out into the shop, pulled the hammer out of my Millenium Pumper, and modified it slightly.... I removed 0.040" from the back end of the adjusting screw to allow one more turn of travel.... I can now recess the hammer 0.25" from the front face, reducing the maximum valve travel to 0.060" at the point the hammer face impacts the valve body.... I set the RVA to a whisker short of coil bind on the 2.00" x 0.045" hammer spring, maxed out the travel, and took a shot at 1800 psi, recording the velocity.... I repeated this, adjusting the position of the travel/lift adjuster.... I then decreased the hammer spring preload a turn at a time and did everything again.... Here are the results....



If you look at the curve for the hammer spring near coil bind (blue line, reading from right to left), you will see that as you increase the hammer travel (and hence the Energy and Momentum) the velocity increases and then plateaus.... This is the expected reaction to increasing hammer strike, as I've demonstrated many times on regulated guns (ie at constant pressure, in this case 1800 psi).... However, the last 2 turns of travel show something different happening.... At about 1 turn out, where the valve lift can no longer exceed about 0.10" without the hammer hitting the back of the valve, the velocity starts to decrease.... In that last turn of travel (1/24th of an inch = 0.042") it drops like a stone.... This is clear evidence that the hammer is hitting the valve, and that the loss of valve lift is killing the velocity.... At 2 turns out, we see the same pattern, with the velocity dropping off during the last turn of adjustment.... At 3 turns out, the dropoff doesn't occur until the lift is less than about 0.080" (1/2 turn out).... and at 4 turns out it doesn't occur at all, with the maximum velocity occurring at maximum hammer travel.... That tells me that at 850 fps, the valve is only opening 0.060" or less at 1800 psi....

Sooooooooooooooo.... the facts fit with the theory.... I can now adjust the valve lift providing that I am running lots of hammer spring preload.... There is one problem, however.... The adjustment, even using 24 TPI (0.042" per turn) is VERY finicky.... One turn (with the spring at coil bind) is over 250 fps.... Considering that, it remains to be seen if there is any practical application.... It will depend on whether or not I can achieve better efficiency running on the "left side" of the curves (where the velocity is determined by valve lift directly) compared to on the "right side" where the velocity is determined by spring preload (and it's effect on lift and dwell).... More experimenting is called for.... and the Millenium Pumper may not the the ideal candidate for that....

Bob