How Does a Float Valve Work?

A float valve is used to shut off the flow of liquids, normally water, at a pre-determined level. When adjusted and working properly a float valve is very accurate and extremely reliable. Float valves are found in nearly every American home as well as in many industrial applications. The concept of the float valve is very simple, which accounts for its reliability and wide spread use.

What is a Float Valve?

How Does a Float Valve Work?

The float valve is used in a reserve water tank and has three primary parts: the valve, the stem and the float device. The valve will block the flow of water through the pipe as the stem rises and creates a tight seal. The stem connects the valve to the float device. In some applications the stem is also used to adjust when the water flow will be blocked. The float device is normally round and filled with air. This device is air tight and is attached to the stem. Due to the trapped air in the float device it has buoyancy and will float atop the water. When the water is released from the reserve the float device drops, opening the valve. The valve will remain open until the float device is raised to a pre-determined level by the rising water. The valve will then be closed and the water supply shut off.

Common Applications

The most common application of the float valve is the standard household toilet. The float valve is located inside the reserve tank on the back of the toilet. Most models have a balloon-shaped float device attached to a stem which extends across the tank to the float valve. When the toilet is flushed the float drops as the water is released and the valve is activated. The tank will then refill and the valve will be closed. The toilet can be flushed again.

Ball Float Valve

Another type of float valve is the "ball float valve." In this application the valve does not shut off the flow of liquid, but instead seals a vent line. A ball float is held in place by a bracket which keeps it properly positioned below a vent line. When the water or other liquid rises, the ball will float up and cover the vent pipe opening. This will prevent any liquids from moving up the vent line. If the seals are working properly this application can also restrict the entrance of more liquid into the reserve tank.