A reciprocating piston/plunger pump inlet manifold includes an elongated cylindrical manifold member closable at opposite ends by transverse end caps connected to the manifold member by releasable couplings. A rubber or polymer liner formed with nitrogen filled closed cells is disposed within the manifold member. Spaced apart fluid discharge guide and mixing tubes are connected to the manifold member and include flanges for securing the manifold to inlet valve housings of a pump. The fluid flow guide and mixing tubes include partitions and a mixing chamber portion of the tubes. Improved fluid flow characteristics with minimal solids separation and minimal fluid velocity or acceleration induced pressure losses are exhibited by the manifold.