A butterfly valve is a valve with a handle in the shape of butterfly like wings, it shuts off with a 1/4 turn of the valve handle. The mechanism inside is a metal ball with a hole through it, turn it one way and it opens water, turn it 1/4 of a turn or 90 degrees and the holes are then blocked off by the sides of the valve body. Very good valve and shuts off water immediately with no leaks, no maintenance.

A gate valve is a valve with either an octagnogle shaped handle or round handle. It shuts off the same way as a normal tap however, a gate valve has no washer of any kind, what shuts the water off is the mechanism inside the valve which is engineered in such a way that the metal disk inside slides up and down inside the valve body with a very fine tolerance shutting off the water. However, gate valves have been known not to shut off water properly either because the tolerance inside is not small enough which allows water to flow through or when the valve gets old it starts to form deposits on the sliding disk which prevents it from closing properly.