Okay, Slug gave the rundown on what would happen if you tried to not use a check valve. I'd like to address a little bit of why.
Over the last few months, I've had several people ask me about combining tanks and resulting air pressure. Let me state a basic principle of NERF blaster pneumatics. When you start pumping a NERF blaster, everything in the system is going to have equal pressure! If you have a Titan airt ank and an AT2K air tank and three big salvo air tanks (no SMDTG trigger) and you pump ten times, you're going to have equal pressure throughout all of these tanks and the tubing connecting them. This pressure would probably be too low to do anything with, so you'd pump it say thirty more times and get it up to 30 psi. Each blast tank/air tank whatever you call it is going to be at PSI. It is impossible to result in different air pressures in each of these tanks. PRESSURE IS EQUAL THROUGHOUT THE SYSTEM!
Now, most NERF blasters do not have check valves in the tanks themselves. Those that do are not typically used in integrations. So if you did not put in any of your own check valves and you fired the Titan tank, the air from the AT2K would empty via the valve opening in the Titan and the back pressure would cause the three big salvo tansk to fire. The air inside the system would now be equal to atmospheric pressure and therefore no more potential energy to launch darts...pulling the trigger will do nothing.
Now let's use the same scenario but add in an SMDTG trigger (attached to the three BS chambers) without any check valves. If you fire the first of the BS chambers, all the air in the Titan and AT2K tank is going to rush out the top of the SMDTG assembly (see my recent description for an illustration of this). There would still be air in the second two BS tanks, but not anywhere else in the system. You could then fire off two more shots from the remaining two BS tanks, then there would be no more potential engergy in the system (no air at a greater than atmospheric pressure).
Now, let's say you fired the AT2K first using this most recent set up. All the air from the AT2K tank, Titan tank, and the FIRST BS tank would rush out of the AT2K valve opening. The reason the other two Big Salvo tanks won't empty is because they are sealed off inside the SMDTG trigger assembly (again, see my recent thread for an illustration to better understand this).
Okay, now let's talk about doing this set up the "right way," that is, with check valves. You'd want to put a check valve before the Titan tank, the AT2K tank, and the SMDTG trigger assembly. If you fired the Titan tank first, all the air in the tubing before the other check valves would rush out the Titan valve opening, but all the air after the check valves before the SMDTG trigger and AT2K tank would stay put and pressurized. You could then fire off the remaining shots in any order and it would work effectively.
Now, if you're wondering how you can get away with one less check valve, here's the answer...always fire the same tank first. If there are check valves on the other two tanks/trigger assemblies, then the air will remain in them when you fire the "unchecked" tank. If you fired one of the others before you fired the unchecked tank, all the air from the unchecked tank would flow out of the opening and be wasted. So you can always get away with one less check valve than tanks (assuming your air input system has a check valve, and just for the record, the MagStrik trigger valve does not keep air from flowing back out once released, so it does not count as an air source with a check valve) if you always fire the same tank first. If you want the freedom to fire in any order, you need to put a check valve on each tank.
I hope everybody understood this. I'm half way tempted to make a video lecture explaining how this works so people can answer there own questions. Teach a man to fish and all that.
edit: I didn't go into detail on the different operating pressures, but a "Marvelous Salvo" set up can handle a much higher pressure than the Titan. Whichever tank has the lowest maximum pressure tolerance becomes your limiting factor and you don't want to pressurize beyond that limit. In this case, it would be the Titan, which is best around 35-40 PSI.
Edited by imaseoulman, 13 September 2008 - 05:32 PM.