Regulated HPA and Hammer Strike

This is just a short post about how hammer strike affects a regulated HPA gun.... There is an optimum balance between regulator setpoint and the hammer strike, just as in a non-regulated PCP.... Adding spring preload (or hammer travel or weight) past a certain point will result in the gun using more air, but no increase in velocity.... Here is an example....

http://i378.photobucket.com/albums/o...Efficiency.jpg

You will note that there is no change in velocity past a certain point as you increase hammer spring preload.... but the efficiency goes down (number of shots per fill goes down) because you are just wasting air.... However, if you go too light on the preload for a given regulator pressure, once the pressure drops below the setpoint, the velocity will actually increase instead of falling off like it normally does.... Here is an example....

http://i378.photobucket.com/albums/o...tHammerHit.jpg

You will notice that when the tank pressure is above the regulator setpoint (in this case 1500 psi) the velocity slowly creeps upwards.... and then once the pressure drops below 1500 psi it climbs quickly before falling off again.... Most regulators have a small amount of "creep", which means that the output pressure is very slightly higher when there is 3000 psi in the tank than when there is less.... Since the hammer strike is very light, that slightly higher pressure keeps the valve from opening quite as far, resulting in a slightly lower velocity.... Once the pressure drops below the setpoint, the valve opens more and more, and the velocity increases, just as in a non-regulated PCP.... Once the velocity peaks, then the velocity drops as the pressure once again falls.... If you are in this situation, the ideal solution is to lower the regulator pressure to where the peak of the velocity occurs, or even less if that is still more velocity than you want/need.... In the above example, the velocity peaks at 840 fps at 1200 psi, so if you want velocities in the 800-820 fps range that would be a good choice for the setpoint....

I hope that understanding this relationship will enable you to get the most out of your regulated HPA gun....

Bob

Just for us dummies- do you have the two charts on/for the same gun?

I don't know why having them on the same gun would make a difference to the concept.... but here are three graphs for a QB 78 regulated at 1500 psi, with a dual power adjuster....

http://i378.photobucket.com/albums/o...BDualPower.jpg

There is two turns (ie 0.100") difference between the two settings on the hammer spring preload.... It was set at 1.7 turns out for the two strings below.... No changes made except selecting high or low power....


http://i378.photobucket.com/albums/o...BHighPower.jpg

Note there are 50 shots from 3000 psi down to the setpoint of 1500, but the preload on high is nearly perfect and the velocity is still within 10 fps down at 1200 psi.... Immediately after that it started to drop quickly....

http://i378.photobucket.com/albums/o...QBLowPower.jpg

On low power, I got 70 shots from 2000 psi down to 1400 and then the velocity started climbing.... It peaked nearly 150 fps above what it was shooting "on the regulator" at about 950 psi, and didn't get back down to the initial velocity until the pressure was all the way down to about 600 psi....

Hope that makes it clearer....

Bob

Didn't need two diagrams from the same gun for a proof of concept- but it's nice to see everything as applied to the same unit- i.e. shot count compared velocity/efficiency and pressure. It also, in my way of thinking, allows someone without the knowledge/trying to pick it up to have a fairly straightforward guideline without any possible confusion to give them a starting point in implementing the concept on their own project.