Pump valve apparatus

A valve comprising:

• a tubular valve body having an inlet, an outlet and a flow passage therebetween;
• a valve seat carried by said valve body at said inlet;
• a cylindrical cage carried by said valve body the interior of which defines a cylindrical enclosure open at the end nearest said inlet and partially closed by an end wall at the opposite end, an aperture being centrally disposed in said end wall providing fluid communication between the interior of said cage and said flow passage, the exterior of said cage and the surrounding portion of said valve body defining an annular chamber which is in fluid communication with the interior of said cage through port means in the cylindrical walls of said cage;
• and
• a ball closure member carried within said cage for limited axial movement therein between a seated terminal position engaging said seat, blocking reverse flow of fluid through said flow passage, and an unseated terminal position engaging said end wall and blocking said aperture, permitting flow of fluid through said port means and said flow passage, in response to a decrease in fluid pressure within said valve body relative to fluid pressure at said inlet.