I have a design that I will probably build this summer, for a WBL with two PCs.
Look at this picture as you read the description below:
So to use it, first the user would close the ball valve that shoots the balloon (directly below barrel), and would open the two valves that lead to the PCs. Then, the user would pump the giant two PC section through the tire valve (located somewhere, if the Tee doesn't work, it can be in one of the PC's caps). Once it is about 100 psi, the user closes one of the PC's ball valves, and load the balloon and shoots it. Once he does this, he closes the ball valve beneath the barrel again, and closes the ball valve of the PC he just used. Then, he opens the ball valve of the PC he has not used yet. The tee would not have any pressure, so the pressure from the second PC going into the tee might make the pressure go down a few psi, but it would be so small you wouldn't even notive the difference. The user then loads another balloon and fires it, thus using up all the pressure in the tank. The reason I did not have the PCs elbowed upwards of down is because the way it is, the PCs would act like a base. If they were elbowed up with the barrel, the WBL would be hard to deal with. If they were elbowed down, the wb...would be hard to deal with. Post any comments about this or any of your own designs. Thanks.