Stop Valves are closed by screwing a rubber gasket down onto a seat in the middle of the
valve. Pros only use small versions that act as
shutoff Valves for fixtures such as sinks and toilets and outdoor sillcocks. Flow is inefficient because of the circuitous route the fluid (water, in most cases) has to follow. It's important to orient the valve in the right direction with the arrow (cast into the side of the valve) aligned with flow direction. That way, water flows against the bottom of the rubber gasket. If the valve is put in backward, the flow will force the gasket away from the top of the
valve.
