What is the difference between a graphite/stainless steel seal and a rubber/metal seal?

A butterfly valve is often the better choice when installation space, weight and cost at larger diameters are important. A butterfly valve has a round disc that turns a quarter turn. It is lightweight, has a short face-to-face length and can be installed between two flanges. At larger diameters, a butterfly valve is also generally more economical than a ball valve.

A ball valve has a bored ball that rotates 90 degrees. In the open position, the bore is in line with the pipeline, giving you a fully unobstructed flow path and a very tight seal. With a butterfly valve, the disc remains in the flow even when open. Ball valves are also available with a straight bore or an L-port, so that the flow can be diverted in another direction.

Both valves are primarily intended to open or shut off a pipeline, not to control the flow precisely. The biggest difference lies in operation. A gate valve is operated with a handwheel that takes several turns, so the gate opens and closes gradually. However, a gate valve is not suitable for precise flow control.

A ball valve is fully opened or closed with a lever in a single quarter turn, and is easy to operate pneumatically (with compressed air). If the flow needs to be controlled precisely, a dedicated control valve is the better choice.