A ball valve is a valve with a spherical disc, the part of the valve which controls the flow through it. The sphere has a hole, or port, through the middle so that when the port is in line with both ends of the valve, flow will occur. When the valve is closed, the hole is perpendicular to the ends of the valve, and flow is blocked. The handle or lever will be inline with the port position letting you "see" the valve\'s position. The ball valve, along with the butterfly valve and plug valve, are part of the family of quarter turn valves. Ball valves are durable and usually work to achieve perfect shutoff even after years of disuse. They are therefore an excellent choice for shutoff applications (and are often preferred to globe valves and gate valves for this purpose).

Ball valve/strainer combo\'s are used on some timer controlled condensate drains.  Although they are not required they do allow the service engineer to shut of certain parts of the compressed air system without having to depressurize the whole system.  Valve inlet is 1/2" MPT and also 1/4" FPT internally threaded for versatility.