The present disclosure provides a high flow coefficient spool valve (50) through one or more changes in the flow path from a conventional spool valve. The body (56) of the spool valve includes spherically contoured internal grooves (68). The spool (58), slidably engaged inside the body (56), includes concave surfaces between seals (62) that is complementary to the spherically shaped internal grooves (68) of the body. The spherical shape of the body internal grooves (68) and/or concave shape of the spool allow more volume and more laminar flow therebetween, resulting in an increased flow coefficient and flow capacity. The body also is formed with transverse port windows in the port that contour into a bore of the body adjacent the spool. A choke volume in the flow is strategically designed in a parallel flow location rather than a perpendicular flow location to promote laminar flow and lessen turbulence to also increase the flow coefficient.