A fluid pump, comprising: a pump body enclosing a first cavity and a second cavity; a first flexible member disposed within the first cavity and defining a first subject fluid chamber and a first drive fluid chamber within the first cavity; a second flexible member disposed within the second cavity and defining a second subject fluid chamber and a second drive fluid chamber within the second cavity; a drive shaft extending between and attached to each of the first flexible member and the second flexible member, the drive shaft configured to slide back and forth within the pump body; a first shift valve disposed between the first flexible member and the second flexible member, the first shift valve configured to move in response to movement of the first flexible member; and a second shift valve disposed between the first flexible member and the second flexible member, the second shift valve configured to move in response to movement of the second flexible member; wherein the first shift valve is moved from a first position to a second position thereof by a mechanical force when the drive shaft reaches an end of a stroke in a first direction, movement of the first shift valve from the first position to the second position thereof causing a pressure of the drive fluid to move the second shift valve from a second position to a first position thereof and switching delivery of the drive fluid from the second drive fluid chamber to the first drive fluid chamber; wherein the second shift valve is moved from the first position to the second position thereof by a mechanical force when the drive shaft reaches an end of a stroke in a second direction, movement of the second shift valve from the first position to the second position thereof causing the pressure of the drive fluid to move the first shift valve from the second position to the first position thereof and switching delivery of the drive fluid from the first drive fluid chamber to the second drive fluid chamber; and wherein the first shift valve and the second shift valve are operatively coupled to deliver a drive fluid to the first drive fluid chamber and the second drive fluid chamber in alternating sequence. a pump body enclosing a first cavity and a second cavity; a first flexible member disposed within the first cavity and defining a first subject fluid chamber and a first drive fluid chamber within the first cavity; a second flexible member disposed within the second cavity and defining a second subject fluid chamber and a second drive fluid chamber within the second cavity; a drive shaft extending between and attached to each of the first flexible member and the second flexible member, the drive shaft configured to slide back and forth within the pump body; a first shift valve disposed between the first flexible member and the second flexible member, the first shift valve configured to move in response to movement of the first flexible member; and a second shift valve disposed between the first flexible member and the second flexible member, the second shift valve configured to move in response to movement of the second flexible member; wherein the first shift valve is moved from a first position to a second position thereof by a mechanical force when the drive shaft reaches an end of a stroke in a first direction, movement of the first shift valve from the first position to the second position thereof causing a pressure of the drive fluid to move the second shift valve from a second position to a first position thereof and switching delivery of the drive fluid from the second drive fluid chamber to the first drive fluid chamber; wherein the second shift valve is moved from the first position to the second position thereof by a mechanical force when the drive shaft reaches an end of a stroke in a second direction, movement of the second shift valve from the first position to the second position thereof causing the pressure of the drive fluid to move the first shift valve from the second position to the first position thereof and switching delivery of the drive fluid from the first drive fluid chamber to the second drive fluid chamber; and wherein the first shift valve and the second shift valve are operatively coupled to deliver a drive fluid to the first drive fluid chamber and the second drive fluid chamber in alternating sequence.