i'm thinking about construcing my own cannons and i'm pretty sure i have all the details down. the only thing i'm not quite sure about is the actuation method for the bunna ball valve. i know the mpa-7s are quite popular but i can't realy find any information on exaclty how much travel they have have. and what the mechanism is like. any pics would be helpfull too. i'm also thinking about using an electric solenoid instead but havn't realy found anything that would fit for the application. any ideas?
MPA-7 (miniature pilot actuator, 7/8 inch dia) This is basically a short, wide piston meant to travel far enough to open larger valves. It has a hollow cylinder body with a cylinder inside as the piston. IIRC, it has 0.5" of travel. Check how much force you will need to open the buna ball valve and compare it to the force applied by the solenoid. The greater the difference, the quicker the valve will open, making for a snappier and more responsive gun. If there isn't enough difference, the gun will open slowly or not at all.
if you consider the diameter of the buna ball seat and the internal bore of the Mpa-7, as long as the buna seat is smaller, it will open, even if the pressure in the accumulator is the same as that which is operating the Mpa-7. That said, if the pressure in the accumulkator is less, the valve will open faster. 0.5 in of travel is more than sufficient to open the buna enough.
i'm looking at the clippard mpa 7, its got a 7/8th bore so i figure it'l be good for a half inch ball valve. i'm wondering how thick the piston/actuator is and how do you attach it to the ball vavle. also will a half inch ball valve be enough air flow for 3 1/4 barrels?
I corrected my earlier mistake about the bore of the MPA-7 (brain fart, sorry, its 7/8", not 7/10" as I initially said). The rule of thumb for cannon design is that the cross-sectional area should be constant or decrease as the air moves through the cannon. Start from the end of the gun, three 1/4" diameter barrels, and calculate the total area: 0.125^2*pi*3=0.147 square inches. The beginning of the air passage must be at least equal to this, but greater is better. A 0.5" bore valve will give you 0.196 square inches, which is greater than the area at the end of the barrels, and so is sufficient for three 1/4" barrels. The rule of thumb for accumulator size is I personally like to be oversize compared to the rule of thumb, both on accumulator volume and valve bore, but that's just me and I'm a bit of a monster sometimes. Here is a thread talking about some of Kotori's and my ideas on cannon efficiency. The good part is near the bottom of the first page. There is also a thread talking about Kotori's and my general rules of thumb for cannon design, but I can't seem to find it. If we do find that other thread, I'd like to consolidate the two and get them stickied so they are more readily available to see, since they cover some important ideas on big gun cannon design.
alirhgt, good stuff but i'm still a little lost here. i'm persuing two options: 1) making a ball valve out of a pvc T fitting with one end of the T going to the accumulator, the opposite end having the actuator mounted in or to with 1/8th rod attaching it to the ball in the valve. the last part of the t going to the gun. now if i build something like this i'm not sure how i could assemble the whole thing and how the 1/8th rod would attach to the actuator. 2) finding a pre built valve that is electronicaly operated. the only thing i'm not sure about with this option is the flow rate required. anybody know what the flow rate is like through .5 inches at 100psi?
Anything pre-built, off-the-shelf, that does the trick in terms of quickness & flow rate, is liable to be large, heavy, & expensive. Likewise for a solenoid, plus it's going to be a power hog. Has anybody ever tried a butterfly valve? Seems to me, that might solve the problems of flow rate & actuation. JM
