How Do Ball Valves Work?



  • A ball valve is a port valve that opens to let water in and closes to shut water off. It is named for the ball inside the valve that rotates. They are used in many areas due to their ease of repair and ability to withstand pressure and temperature. Depending on what they are made of, ball valves can hold up to 10,000 pounds per square inch and around 200 degrees Celsius. They range in size from a quarter-inch opening to a foot wide or larger.

Set Up

  • The valve is made up of a outer shell, a ball with a hole in it and a handle. These are the main components. To look at the valve simply, the ball inside the shell plugs up the valve opening. A handle attached to the ball can turn the ball from outside the valve shell. The ball has a hole through the middle that will allow water to pass. When the handle is turned to the open position the hole in the ball is facing the same direction as the valve shell. To turn it off, the handle is moved and the ball turns with the hole facing the sides of the valve wall.


  • The ball valve comes in several variations. The full port valve has a hole in the ball that is the same dimensions as the pipe that it is attached to. This keeps water from being restricted as it flows. The reduced port valve creates an opening in the ball that is smaller than the pipe. This creates less water flow. A trunnion valve has a pin securing the ball so that it doesn't dislodge. This is for high velocity flow. There are three- and four-way valves, as well. With these the flow is altered by the position of the ball. The hole in the ball of the valve is normally shaped like a T or L. When it is a T it can allow flow in two directions at once or one direction with the other side closed. When it is an L shape it allows flow in only one direction at a time.

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