A pump is disclosed, having a pumping chamber in the rotor. The rotor is rotatable between first, second, third and fourth positions. When the rotor is in the first position, an inlet cam assembly displaces a piston to draw fluid into the pumping chamber via a first housing inlet. When the rotor is in the second position, an outlet cam assembly displaces the piston to expel fluid out of the pumping chamber via a first housing outlet. When the rotor is in the third position, the inlet cam lobe assembly displaces the piston to draw fluid into the pumping chamber via a second housing inlet. When the rotor is in the fourth position, the outlet cam assembly displaces the piston to expel fluid out of the pumping chamber via a second housing outlet. A method of pumping fluid is also disclosed.