Variable pre and de-compression control mechanism and method for hydraulic displacement pump

A hydraulic pump, comprising:

• a rotating piston carrier, having first and second ends, including piston chambers therebetween, supported for rotation in an enclosed pump casing;
• 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 an aligned respective first intake inlet and discharge outlet associated with the pump casing, the valve plates being suspended 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 one of the plurality of hollow pistons is passing the corresponding land area, the respective hollow piston is sealed, and fluid flow into and out of the hollow 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 independent control, 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.