[PSUBS-MAILIST] Life support

Can any do me a favor and possibly describe there subs life support system. What is better an air supply or a pure oxygen supply with C02 scrubbers. How are you maintaining the 1atm of pressure? I am not looking for a long or deep diving setup. I'm looking to use a MAX of 4 SCUBA tanks to support 2 people. Dive depth would be less than 50 feet. Any help would be greatly appreciated or if anyone has a specific thing I can research that would also be very helpful.