Breathing Resistance in Scuba Regulators

The single-hose two-stage demand regulator is the most common means of supplying divers with gas. As diving conditions become more severe, this regulator sometimes exhibits excessive breathing resistance. This paper discusses breathing resistance and its sources, including: (1) Respiration and breathing resistance (2) Description of regulation system (3) Regulator operation (4) Sources of breathing resistance (a) Hydrostatic differential (b) Valve friction (c) Setup bias (d) Valve spring compression (e) Valve unbalance (f) Pressure drop across mouthpiece (g) Pressure drop across exhaust valve (5) Recommendations for improved operation.