Philips S91 Series Manual page 18

ENGLISH
18
3 Remove the shaving heads from the shaving head holder. Each shaving
head consists of a cutter and guard.
it may take several weeks before optimal shaving performance is restored.
4 Clean the cutter and guard under the tap.
5 After cleaning, place the cutter back into the guard.
6 Put the shaving heads back into the shaving head holder.
7 Place the retaining ring holder on the retaining ring (1), place it
on the shaving head (2) and turn it clockwise (3) to reattach the
retaining ring.
Repeat this process for the other retaining rings.