Valves: what sort where? All aspects of plumbing questions and answers, help, tips and information

[RoyG]

When I look at plumbing fittings, I see several different styles of valve. Stopcocks, gate valves, in-line isolating valves with either a screw head or a small plastic lever, and one other sort with a fairly large brass lever.

I was just wondering what different uses each of these have. I know the ones with screw heads are for isolating taps and washing machines, but what are the basic difference in uses between the other sorts?

[plumbbob]

Stop taps have rubber washers and and will stop cold water at high pressure.

Gate valves are not guaranteed 100% watertight but have a long life when controlling hot water so would normally be used to isolate various heating and hot water circuits. They also open fully, so unlike other valves, don't restrict flow.

Ball valves with the plastic handle you describe often can be used with water, but are more likely to be used to isolate gasses or compressed air.