The Basic Anaesthesia Machine. CL Gurudatt ... the N 2 O pressure regulator was constructed in such a way that pressure of the O 2 flow was required to release the flow of N 2 O. So, N 2 O regulator was made to act like a 'slave' regulator to O 2 as the 'master' regulator. ... (Orings) at both ends of the flow .