Model 351 cylinder flowmeter regulator is zero-compensated for more efficient gas use. The unique design of this flowmeter makes it more resistant to carbon dioxide (CO2) freeze-up than comparable competitive models. This flowmeter features a durable, easy-to-read, flow tube and cover, a gaugeless brass body, large plastic knob for precise adjustments and one-piece encapsulated seat desgin with internal filter and PTFE TeflonĀ® seat to protect it from particulate contamination.