A new pump design is described. The pump features a casing with a continuous enclosure extending from a power end of the casing to a fluid end of the casing for housing the reciprocating assembly of the pump, which includes a crankshaft, a plurality of control rods coupled to the crankshaft, and a plurality of crossheads coupled to the control rods. A detachable lid is attached to the casing at the power end and the fluid end of the casing, and encloses the reciprocating assembly. An alignment plate oriented substantially parallel to a stroke axis of the pump maintains alignment of the crossheads.