An improved manifold and valve cartridges suitable for high power (over 600 hp) reciprocating pumps for water blast or jet applications are disclosed. In one aspect, the disclosed valve cartridges are compact and mounted axially along a seat member that has a central bore in addition to suction and discharge seats. The seat member can also be provided a plurality of radially arranged bores for allowing suction flow to the pump. A spool valve assembly can be mounted through the seat member bore, and can include a valve spool, a spherical suction valve member, a compression spring, and compression-locked rings. The spool valve can include a closed flanged end that engages with the seat member discharge seat. In operation, the compression spring continuously pushes the spool valve closed flanged end against the discharge seat and pushes the suction valve member against the suction seat to retain a normally closed position.