Those ball valve type air misters seem to require a lot of air to get them to work properly. My vacuum pump was allowed to move enough air to drop under 12psi running just one mist line due to the larger orifice openings of the mist line. I found that they would need at least 15psi of air to start drawing water. But, this pressure was also dependent on the height of the water tank in relation to the mist line.
Say you have water in the tank and you run the pump to get air going through the mister. You can probably picture that the water tank will need to be lower than the mist line so a syphon effect does not dump all the water. So, here we are waiting for the water to make it through the line to the nozzle and the water is having too much difficulty making it into the mist line. At this point, one option would be to just grab the tank and lift it up a bit to help the water flow. It makes it into the mister and goes from nothing to way too much. One option would be to drop the pressure a little bit and try to lower the differential in the system so water stops flowing to much. The issue is that balancing this rate is pretty sensitive and the pressure would need to be adjusted in fine amounts. Very hard to achieve using a ball valve. Also, restricting flow would mean that once the pump is shut off, then it beings all over again because the next time the pump is turned on there will be far too little pressure to draw water back through the line.