GF DIASTAR Six Manuel D'utilisation page 51

Installation
 Open housing nut, see fig. 13. Use a strap wrench/ special tool for open it.
 Turn actuator in 90° intervals to the desired position.
Fig. 14
 Realign diaphragm parallel to the compression piece. Diaphragm tabs must be
positioned between the narrow guiding bars of the inner housing, see fig. 14
 Move the valve into the "open" position, see fig. 12
Fig. 15
 Position actuator on the valve body and tighten housing nut handtight, see fig. 15
Diaphragm is now centered.
Instruction Manual
49