Direction of the FlowMost U.S. Solid Valves are UNIDIRECTIONAL
Make a note of the arrow on your valve. Most U.S. Solid valves are unidirectional. This means they are intended to flow in one direction only, in the direction of the arrow. If connected in opposite directions, the valve will not actuate properly (will not close for Normally Closed valves). Additionally, be sure the medium passing through is filtered. If not, particles will cling to the gasket over time, which can cause it to not seal properly.