46 CFR § 197.310 - Air compressor system.
A compressor used to supply breathing air to a diver must have -
(a) A volume tank that is -
(1) Built and stamped in accordance with section VIII, division 1 of the ASME Code with -
(i) A check valve on the inlet side;
(ii) A pressure gage;
(iii) A relief valve; and
(iv) A drain valve; and
(2) Tested after every repair, modification, or alteration to the pressure boundaries as required by § 197.462;
(b) Intakes that are located away from areas containing exhaust fumes of internal combustion engines or other hazardous contaminants;
(c) An efficient filtration system; and
(d) Slow-opening shut-off valves when the maximum allowable working pressure of the system exceeds 500 psig.