A hydraulic displacement pump, comprising: a rotating piston carrier, having first and second ends, including piston chambers therebetween, supported for rotation in an enclosed pump casing (15, 16); a plurality of hollow pistons, inserted into respective pistons chambers, from each of the first and second ends, and carried for collective rotation within the pump casing via the piston carrier, the pistons being driven in pumping action via a pair of respective floating piston plates connected to each of the respective pistons opposing each of the first and second ends of the piston carrier; first and second valve plates having openings therethrough, for controlling flow of fluid to each of the plurality of pistons from aligned respective first intake and discharge plenums associated with respective sides of the pump casing, the valve plates being movable valve plates configured for incremental rotation in opposed end sections of the casing and opposed to the pistons, the valve plates including respective land areas, between the openings, wherein when a piston is passing the corresponding land area, the respective piston is sealed, and fluid flow into and out of the piston is momentarily stopped, the valve plates being configured to increment in rotation with respect to the rotation of the piston carrier in either a forward or rearward aspect, so as to alter the positional phase of the land area of the valve plate with respect to overall pump operation, wherein: the respective first and second valve plates are configured for separate independent control of the respective valve plates enabling shortening and lengthening of the effective land area of valve plate operation and thereby create de and pre-compression of fluid within the piston chambers when compared to fixed position valve plate pump operation. a rotating piston carrier, having first and second ends, including piston chambers therebetween, supported for rotation in an enclosed pump casing (15, 16); a plurality of hollow pistons, inserted into respective pistons chambers, from each of the first and second ends, and carried for collective rotation within the pump casing via the piston carrier, the pistons being driven in pumping action via a pair of respective floating piston plates connected to each of the respective pistons opposing each of the first and second ends of the piston carrier; first and second valve plates having openings therethrough, for controlling flow of fluid to each of the plurality of pistons from aligned respective first intake and discharge plenums associated with respective sides of the pump casing, the valve plates being movable valve plates configured for incremental rotation in opposed end sections of the casing and opposed to the pistons, the valve plates including respective land areas, between the openings, wherein when a piston is passing the corresponding land area, the respective piston is sealed, and fluid flow into and out of the piston is momentarily stopped, the valve plates being configured to increment in rotation with respect to the rotation of the piston carrier in either a forward or rearward aspect, so as to alter the positional phase of the land area of the valve plate with respect to overall pump operation, wherein: the respective first and second valve plates are configured for separate independent control of the respective valve plates enabling shortening and lengthening of the effective land area of valve plate operation and thereby create de and pre-compression of fluid within the piston chambers when compared to fixed position valve plate pump operation.