Weed sprayers are canisters that hold a mixture of water and liquid fertilizer or herbicides. You pump the handle located on top of the canister to create pressure inside the canister. Once pressurized, you can pull the trigger on the canister wand and spray your lawn with the fertilizer or your weeds with the herbicide. You need to take some precautions if you plan to remove the lid from the weed sprayer if you do not want to spray yourself with the chemicals inside the canister.
Point the wand at an area with weeds that you want to spray and then pull the trigger to spray the chemicals onto the weeds until the sprayer stops spraying. Once no more fluid comes from the wand, the canister no longer has pressure built up in it.
Put on a pair of work gloves to protect your hands from any foam created inside the canister. If the canister is empty, you will likely not have a large amount of bubbles, but if the canister still has a moderate amount of chemical left in it, you will likely experience bubbles that could hurt your skin.
Place the canister on the ground and grip the canister in one arm. If you choose, you can grip the canister between your knees so you can use both hands to remove the lid.
Grip the lid, not the handle on the lid, and turn the lid counterclockwise until you completely thread the lid off the canister.
Lift the lid off the canister slightly and shake the pump connected to the bottom of the lid several times to knock off any bubbles or excess fluid.