Q: For the Model 78,  when it impacts it seems to exhaust a lot of air. This is normal correct? Its just some sort of a quick exhaust?

A: The seals are design to release the air when the marker contacts the part. The cylinder is not design to remain in the extended position, 

Excerpt from Operation Guide:

Electrical Sequence for Double Solenoid Valve: To advance marker, energize solenoid “A”. To return marker and reset, deenergize solenoid “A” and ENERGIZE solenoid “B”.

Electrical Sequence for Spring Return Valve: To advance marker, energize solenoid “A”. To return marker and reset, de-energize solenoid “A” after part is marked. 

Speed Control Adjustment: Adjust speed control “R” to control speed of retract motion. DO NOT install speed control on forward (rod) port of marker. 

Note: For most efficient operation, electrical signal energizing solenoid “A” should be very short, approximately .06 to .10 seconds.

Model 78 Operation Guide