[Chris Fultz]

My perception of the why for this rule -

#1. There are many things you could do to a pneumatic cylinder that would be completely safe. These modifications would not affect the integrity of the "pressure vessel" portion of the cylnder and the pneumatic could be as safe as a new one off the shelf.

#2. There are also many things you could do to a pneumatic cylinder that might look completely safe, but would affect the integrity of the "pressure vessel". These changes could seem simple and safe, but after repeated cycling of pressure / no pressure, could cause a failure.

And from a safety perspective, it can be extremely difficult to tell the difference between modifications that fit #1 and the ones that fit #2.

And so, to be safe, FIRST does not allow ANY modifications to pneumatic components, so that a modification does not get missed at inspection, and so that an inspector does not have to turn into a specialist to determine if a modification is safe or not. Very few people have this experience or expertise, and in reality, only the component OEM could really tell you if a modification was safe, because only they know what their design is capable of and the margins they have built in.

A pneumatic component failing at 120 PSI or 60 PSI could be a major event. Ruptured metal, pieces flying, a sudden move of a component that is in place, etc.