Much more rugged. Longer life. Much bigger plenum chamber (2nd stage plenum chamber is 5 times the volume of 1st stage plenum chamber) ensures : - Outlet pressure stability. Steady flow of gases. Fire-retardant valve material. Stainless Steel Diaphragm in 1st stage - can withstand stock of full cylinder pressure. Neoprene valve in 2nd stage - Gives flexibility and better pressure regulation.