Siemens SIPART PS2 6DR50xx Manual page 20

Design and Functional Principle
20
The exhaust air output E can be provided for supplying dry instrument
air to the tapping chamber and spring chamber to prevent corrosion.
Figure 2-6, page 21 shows the pneumatic connection variants for the
different actuator types, the positioning action and the safety position
after power failure.
SIPART PS2 Manual
A5E00074631--06