[Al Skierkiewicz]

Karthik,
It is my understanding of the intent of this rule is that only one compressor be used for competition. If that fails, as in other components, it may be replaced. It is my understanding/opinion that rules are in place to avoid even the hint that one team can have even a small advantage over another.
Eric, that wording was considered as rule verbage in the past. Simplicity was the deciding factor in that decision.
As to the other ideas about valves and holding air, the ultimate result must be to release all stored energy at the end of a match to force the robot into it's minimum energy state for transport. I most heartily agree with designing your system so that it does not move when enabled or disabled. My arm was crushed during an inspection when the arm fell during the power on tests when I asked for the robot to be disabled.
As to the pressure transducer operating the compressor, I came across more than one robot this year that used that method only to find out that the software was programmed to increase pressure above the specified 120 psi during certain conditions. In one case the max pressure was 145 psi. It was caught by an observant ref who doubles as an inspector for some events.
While some of these items may seem like nitpicking, please put yourself in the position of being a team who was beat in a critical match and then finds that the team that beat them had that second compressor filling their tanks or that system pressure was above 120 psi. Oh yes, I just remembered my wife looking at a team in the queue with a battery and some alligator clips asking me "what are they doing over there?" Only to find that there were running the compressor from a robot battery to run the pressure up to maximum before they took the field. When I checked, the pressure appeared to be close to 150 psi before the team opened their dump valve. Of course we reinspected and re-calibrated the pressure relief valve for 125 psi and gave the team a stern warning.