16-litre knapsack sprayer (also called a backpack sprayer or manual agricultural sprayer).
It’s used for spraying pesticides, herbicides (weed killers), insecticides, fungicides, fertilizers, and disinfectants on farms, gardens, lawns, and crops. The tank is worn on the back like a backpack, and you pump the lever by hand to build pressure, then spray through the lance/nozzle.