A ball valve consists of the disk-shaped valve seat and hollow metal ball that is partially filled with the liquid to shut off and prevent the flow. Since it uses the principle of pressure balancing, it's widely used in many industries including water systems, gas systems, solar power systems and other places where fluid flow must be stopped or allowed. The design of a ball valve is very simple. It consists of a hollow metal ball that is partially filled with the liquid. When you press on the outer part of the valve, it will make a pressure difference that will cause the disk-shaped valve seat to be pressed against the wall of pipe and form an obstruction to stop or allow fluid flow through it. The miniature plastic ball valves are usually used in small systems of solar water heating systems and some special purposes. Plastic ball valves are used in the solar system to stop or allow flow of the liquid when adjusting heat output. When you adjust output, you need to stop the hot water from going further by turning off the valve on top of the manifold (usually made from PVC pipe), then open or close the plastic ball valve (at the bottom of manifold) to adjust temperature. A Ball Valve used to cut off flow in pipes and prevent backflow. The ball is moved up or down in a pipe with stem and handle. Not often used as shut-off valves since they require 2 connections to the pipeline. Where space is limited they are very useful. The ball has to be pushed up or down and rotated, these valves can be easily operated with just one hand. Ball valves are used in washing machines, dishwashers and other water consuming equipment. They have a ball shape with 1 or 2 sealing rings.