There are already known pump units comprising a drive shaft (2) and a rotatably arranged rotor (3) that is driven by the drive shaft (2), wherein the drive shaft (2) has an inclined sliding surface (4) on an end side, which permits the rotor (3) to move back and forth by its rotor axis (5) about a drive axis (6) of the drive shaft (2), wherein the drive shaft (2) has a first bearing section (18) facing towards the the rotor (3), and a second bearing section (19) facing away from the rotor (3). The first bearing section (18) of the drive shaft (2) is arranged in a first sliding bearing (20), and the second bearing section (19) is arranged in a second sliding bearing (21). The load-bearing capacity of the sliding bearing facing towards the rotor (3) is limited up to a predetermined working pressure in the pump unit. In the pump unit according to the invention, the load-bearing capacity of the sliding bearing (20) facing towards the rotor (3) is increased. According to the invention, the diameter of the first bearing section (18) of the drive shaft (2) and the first sliding bearing (20) is respectively larger than the diameter of the second bearing section (19) and the second sliding bearing (21).