A valve assembly (100) for a penis pump (1102), comprises a valve cap (110) comprising a hole (115)； and a valve stem (120) extending through the hole (115) in the valve cap (110). The valve assembly (100) is adapted such that axial motion of the valve stem (120) causes the valve stem (120) to mechanically interact with the valve cap (110), so that the valve stem (120) moves between a first position, in which the valve stem (120) seals a pump chamber (1108) of the penis pump (1102), and a second position, in which the valve stem (120) operates as a one way valve. Accordingly, axial motion of the valve stem (120) is used to select the function of the valve assembly (100).
