The support of a shaft (7) which is rotatably supported in through-holes of the housing (1) of a pressure chamber in bushes (11, 12) provided with sealing rings and which is secured against axial displacement by securing rings (21, 22) is to be improved in such a way that a low-wear and secure arrangement of the shaft (7) and bearing bushes (11, 12) is achieved. For this purpose, it is suggested that each through-hole (9, 10) of the housing (1) comprise a collar (15, 16) which projects radially inward and forms a support for a projection which is directed radially outward and with which each bush (11, 12) is provided, the front side (19, 20) of the latter facing the pressure chamber simultaneously forming a support for a securing ring (21, 22) arranged on the shaft (7), wherein the two bearing sides of the shaft (7) have the same diameter.