hand wand application, i would most likely prefer an "on demand 12v sprayer pump" it has a little pressure switch built into the pump, so it only turns on when you use the hand wand.
PTO pumps, seem more of a hassle for spot spraying / hand wand. no easy way to turn pump off, while you have hose stretched out doing things.
you can setup a electrical sprayer, for some boom setups. but once you get up into the larger "wider booms" electrical sprayer pump may not be choice, more so if ya looking at doing field work or large yards or like. and that is were a PTO pump will more likely shin, IMHO.
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i would skip a 3pt option, and get a 3pt carry all, or a pull behind, over the years, it is nice to use truck, car, atv, etc... to spray vs hooking up to tractor.
as much as pull behind stuff annoys me, when it comes to backing them up. (wanting to jack knife on you very easily and quickly) it makes for a more universal setup that can be pulled by multi things, including riding lawn mowers. and with wheels already on it, it makes for easy unhooking, and finding a place for it in the shed.
for the smaller wheel barrow like tires, put some closed cell spray foam in the tires. and never worry about wheels going flat in the pull behind.
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skid/atv/utv/flat bottom, FEL, 3pt carray all. other words a flat bottom sprayer, some of them do come with some boom options.
picking up a 12v marine battery works good enough without needing to wire directly to a tractor / vehicle / atv. granted hooking directly to pulling unit will give you a longer usage. but *shrugs*
the better booms have a spring or break away option, (they bend backwards) if you hit boom with something. so the booms and what ever you hit don't get destroyed and all mangled up.
ability to adjust the booms UP and DOWN, and to swap out the nozzles for the boom sprayers is a must. so you can control the spray pattern and misting, and keep the chemicals from blowing away before they even get to what you want to spray. along with ability to adjust for different chemicals
i have a small "filter" between tank and pump, to protect the pump from stuff, and then each boom sprayer/mister, has a built in little filter, to help keep the boom sprayers from plugging up. it may seem like a hassle, but keeps me going longer, before i need to do maintenance and clean or replace all the little boom sprayer filters.
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cleaning the bloody tank out.. and having good drain spots is big issue with tanks. along with a "man hole" large hole were you can stick garden hose nozzle down and spray the inside down.