Cashco Siemens PS2 I/P - Manual (Page 19)

Design and Functional Principle
19
SIPART PS2 Manual
A5E00074631-01
The exhaust air output E can be provided for supplying dry instrument
air to the tapping chamber and spring chamber to prevent corrosion.
Figure 2-5, page 20 shows the pneumatic connection variants for the
different actuator types, the positioning action and the safety position
after power failure.