Ball, gate or butterfly valve?

All three open and close a pipe. They are built for different sizes and different jobs.

Ball valve

A quarter turn of the handle opens or closes it. Quick, tight and the most common valve on small lines (up to about 2 inches). A full bore ball valve has a hole as big as the pipe; a reduced bore one is cheaper but slows the flow a little.

Gate valve

A wheel you turn many times to lift a gate out of the way. Fully open, it hardly slows the flow. It is slow to close, which is gentle on long pipes (no water hammer). Common on water mains and larger lines.

Butterfly valve

A disc that turns in the pipe. Light, short and much cheaper than the others in big sizes (from about DN50 up). It fits between two flanges.

Not for half-open

Ball and gate valves are for fully open or fully closed. Left half open to control the flow, the seat wears and the valve starts to leak. To control flow, use a globe valve or a control valve. A butterfly valve can control flow roughly.

What to tell the seller

• Size (inch or DN) and the end type: threaded or flanged (and which flange standard).
• Pressure class, for example PN16.
• What flows inside and how hot: brass for water and air; steel or stainless for steam, oil and chemicals.