A submersible pump assembly for transference of a fluid medium with low viscosity, the submersible pump assembly comprising: a cylinder block having a plurality of cylinders (122, 124) formed therein; a first port located in fluid communication with the plurality of cylinders (122, 124) and a suction chamber; a second port located in fluid communication with the plurality of cylinders (122, 124) and a pressure chamber; a third port located in fluid communication with the plurality of cylinders (122, 124) and the suction chamber; a respective plurality of pistons (126, 128) slidably received in each of the plurality of cylinders (122, 124); a drive shaft rotatably supported in the cylinder block, the drive shaft being coupled to a drive unit; an inclined leading plate coupled to the plurality of pistons (126, 128) and the drive shaft, the inclined leading plate coupled to the plurality of pistons (126, 128) such that the plurality of pistons (126, 128) are configured to be axially driven in a reciprocating motion within the plurality of cylinders (122, 124) upon rotation of the inclined leading plate; a first operational mode wherein the fluid medium is transferred from the first port to the second port during the reciprocating motion of the plurality of pistons (126, 128); a second operational mode wherein the fluid medium is transferred from the first port to the third port; and a valve plate having a first position and a second position, the valve plate selectively actuatable under control of a drive member between the first position and the second position, the first position corresponding to the first operational mode, the second position corresponding to the second operational mode. a cylinder block having a plurality of cylinders (122, 124) formed therein; a first port located in fluid communication with the plurality of cylinders (122, 124) and a suction chamber; a second port located in fluid communication with the plurality of cylinders (122, 124) and a pressure chamber; a third port located in fluid communication with the plurality of cylinders (122, 124) and the suction chamber; a respective plurality of pistons (126, 128) slidably received in each of the plurality of cylinders (122, 124); a drive shaft rotatably supported in the cylinder block, the drive shaft being coupled to a drive unit; an inclined leading plate coupled to the plurality of pistons (126, 128) and the drive shaft, the inclined leading plate coupled to the plurality of pistons (126, 128) such that the plurality of pistons (126, 128) are configured to be axially driven in a reciprocating motion within the plurality of cylinders (122, 124) upon rotation of the inclined leading plate; a first operational mode wherein the fluid medium is transferred from the first port to the second port during the reciprocating motion of the plurality of pistons (126, 128); a second operational mode wherein the fluid medium is transferred from the first port to the third port; and a valve plate having a first position and a second position, the valve plate selectively actuatable under control of a drive member between the first position and the second position, the first position corresponding to the first operational mode, the second position corresponding to the second operational mode.