A pump includes a stator (4) and a rotor (6) slidably and rotatably mounted at least partially in the stator (4), the rotor (6) comprising a first axial extension (24) having a first diameter (D1) and a second axial extension (26) having a second diameter (D2) greater than the first diameter. A first valve (V1) is formed by a first valve seal (18) mounted on the stator (4) around the first axial extension (24), in conjunction with a first channel (42) in the rotor (6) that is configured to allow liquid communication across the first valve seal (18) when the first valve (V1) is in an open position. A second valve (V2) is formed by a second valve seal (20) mounted on the stator (4) around the second axial extension (26), in conjunction with a second channel (44) in the rotor (6) that is configured to allow liquid communication across the second valve seal (20) when the second valve(V2) is in an open position. A pump chamber (8) is formed between the rotor (6) and the stator (4) and between the first valve seal (18) and second valve seal (20). The stator (4) further comprises a dead-zone seal section (40) surrounding a dead-zone volume (39) formed between the rotor second axial extension (26) and the stator (4), so that any gas bubbles formed in the pump chamber (8) can be captured at least partially in the dead-zone volume (39), which improves accuracy during the expulsion phase of the pump.
