I still need to do some more experiments with nozzles, but in the meantime I have started on the design of a controller for a solenoid. The ball valve is somewhat unwieldy to use in practice, a trigger mechanism would be much better.
As I do not have access to a push button operated valve that is high pressure rated I'm going to use a 12V solenoid valve I got from ebay.
It is rated at 130PSI and so is OK for the pressures in my system.
I'm going to control it with a small micro controller so I can operate it in one of several modes:
Three Shots Rapid,
The trigger will be a push button switch and the mode changed with a seconds push button. The controller will indicate the new mode with audio feedback from a buzzer.
I'm using a Microchip PIC for this design as I am familiar with them and I already have all the development tools.
Here is the schematic drawn with the fantastic Kicad.
The power for the circuit will be supplied by 8 x AA batteries.