Complex sentence: The terms "regulator" and "demand valve" are often used interchangeably, but a demand valve is the part of a regulator that delivers gas only while the diver is breathing in and reduces the gas pressure to ambient.
Split into simpler sentences: The terms "regulator" and "demand valve" are often used interchangeably. But a demand valve is the part of a regulator that delivers gas only while the diver is breathing in and reduces the gas pressure to ambient.