[MrForbes]

I think both of Eric's answers are right. Look at the pressure switch on a "big" air compressor (such as in a shop), it's a lot larger than the little Nason one we get, mainly to have room for contacts and springs and a pressure diaphram big enough to handle the current load. Since ours runs on 12v instead of 120/240, the current load is similar. And the safety thing....the field personnel need to be able to turn off all robot operations, they can't turn off the compressor if it's not under computer control.