we got a few of these 4 gal battery powered back-paks handy to have....when it operates correctly heres the problem, half of them do not operate corectly. All were purchased this spring. this is whats happening, turn on the on/off switch and the things begin spraying automaticly without using the wand lever to turn it on. This is not a huge problem because we only use these sprayers for mosquito control and some shrub insect control. It would be a problem if we used them for herbicides! But regardless what we use them for we would like them to operate properly. The other thing is that they continue to 'flow' even with the power switch off. Gravity siphons material out of the backpack, so we need to keep that wand up over our heads while walking and when storing them in the truck the wands need to be secured up higher than the backpack itself or we lose product. So, whats happening? What do we need to do to fix this? You know, we try out these new technologies to help make the job easier and to get things done quicker...but all they seem to do is cause more aggravation.