A human-powered pump assembly includes a frame and a treadle pivot attached to the frame, such that the treadle pivot defines a horizontal rotational axis. The pump assembly includes a pair of treadles coupled to the treadle pivot and a rocker pivot attached to the frame, such that the rocker pivot defines a separate horizontal rotational axis. The pump assembly includes a reciprocating rocker coupled to the rocker pivot and to the pair of treadles to constrain the motion thereof, such that the rocker pivot axis is located below the treadle pivot axis.

A valve cover lock assembly for a pump having a fluid end module can include a ring adapted to couple to the module, an insert comprising a plurality of segments, and a cone adapted to couple with the insert, wherein the ring comprises a first coupler and the insert comprises a second coupler configured to couple with the first coupler, wherein the cone is configured to move one or more of the plurality of segments when the cone is moved, and wherein the first and second couplers are adapted to at least partially resist movement of the insert. A method of locking a valve cover can include coupling a ring to a valve cover opening, disposing an insert comprising a plurality of segments at least partially within the ring, coupling an actuator to the insert, and coupling the insert to the ring.

A valve cover lock assembly for a pump having a fluid end module can include a ring adapted to couple to the module, an insert comprising a plurality of segments, and a cone adapted to couple with the insert, wherein the ring comprises a first coupler and the insert comprises a second coupler configured to couple with the first coupler, wherein the cone is configured to move one or more of the plurality of segments when the cone is moved, and wherein the first and second couplers are adapted to at least partially resist movement of the insert. A method of locking a valve cover can include coupling a ring to a valve cover opening, disposing an insert comprising a plurality of segments at least partially within the ring, coupling an actuator to the insert, and coupling the insert to the ring.