A float valve, which regulates fluid levels by using a float to control the level of water in a tank, is used in many household devices. The most obvious application for float valves is in toilet tanks, but they also are used in heating and air conditioning systems. These kinds of float valves are designed for a specific purpose and cannot be made yourself at home. However, using the same basic principles, you can construct a float valve for other applications, such as a sprinkler system for your garden. A water reservoir running dry can cause damage to your pump and cause your plants to die of thirst. A simple homemade float valve can prevent this.
Unscrew the plastic nut at the intake end of the hose attachment (the part where the hose attaches) with the pliers. Once this is removed, use the pliers to unscrew the spray nozzle of the hose attachment. This should twist off just like a nut, allowing you to remove the inner workings of the sprayer. These should consist of a plastic washer and a shaft with a spring coiled around it.
Widen the hole in the washer with the drill so that it fits onto the shaft. Remove the coiled spring from the shaft and discard it. Then replace the shaft through the loop in the top of the handle and into the barrel at the top of the spray attachment. Push the washer onto the end of the shaft before the handle; this will stop the shaft sliding completely through the loop of the handle. Reattach the nuts and nozzle.
Fill the plastic water bottle one-third of the way up with water. This is the weight that pulls the handle of the sprayer down, but at the same time there is enough air left in the bottle for it to be buoyant in the water reservoir, closing the handle when the water level in the reservoir is sufficient to support it.
Drill a hole in the handle of the sprayer and twist and push the coat hanger wire through the hole. Twist the wire around the handle to make it secure. Twist the other end of the wire securely around the neck of the water bottle. Place the float in the water reservoir and connect the spray attachment to your water system. When the water level drops, so will the float, opening the valve and refilling the reservoir until the water level is high enough to close the valve.