Both ball valve and butterfly valve are rotary types of a valve. Here, I will cover the topic on both the ball valve and butterfly valve.
BALL VALVE :
As the name suggests it contains a ball with passageway cut through the centre allow a flow of the fluid to pass through it.
When passageway is in parallel with the flowing fluid then a valve is fully open and if perpendicular to flow then the valve is fully closed.
In the below figure you can see a cut view of the ball valve with its parts.
The ball valve's ease of use, ease to maintenance allow it to mostly used in the plant. It can handle up to 1000 bar of the pressure and temperature up to 400 °C.
Valve bodies are made up of metal, plastic or of ceramic metal. Balls are made up of chrome plated.
Ball valve are mostly used in every industrial application provide fine control but they are hard to use as a throttling valve.
BUTTERFLY VALVE :
Another type of valve most widely used valve in the industry. They come with the on/off application and also come with actuator for the precise control.
It contains a rotating disk to control the flow of the fluid. Like ball valve disc always stay in the flow when wide open, which cause a pressure drop.
Due to its cost-effectiveness then other valve and ease to maintenance make them popular in the industries.
Following is the image of the butterfly used in the dairy industry for the application of acid and caustic.
Second pic of the butterfly valve which is used in steam service. Periodic maintenance is required to prevent leak.