halocline
Contributor
Balanced first stages are designed so that the intermediate pressure, which is the pressure exiting the first stage in the LP ports heading to the 2nd stage, stays the same throughout virtually the entire range of pressure from the tank. Unbalanced first stages will experience a gradual drop in IP as the tank pressure gets low. If this is coupled with an unbalanced 2nd stage, there will be some increase in breathing resistance at low tank pressures. My MK2/R190 (both unbalanced stages) starts to breathe a little more stiffly at pressures under 500PSI. IMO, this is not a big disadvantage; it's not like the reg cannot deliver enough air at low pressures, it's more like a noticable increase so that a diver who is very low on air would get a "reminder" that his air supply is running low. In some cases, like a failed SPG or simply an unattentive diver, this can be a safety feature, as the alternative would be continued easy breathing right up until there is literally a breath or two left.
Balanced 2nd stages are designed so that fluctuations in IP do not affect the breathing resistance as much as with unbalanced 2nds; they are held closed by much lighter springs, and some of the downstream air pressure from the 1st stage is contained in a chamber and assists in keeping the valve closed. One advantage of balanced 2nds is that when they are not being used, the spring pressure on the orifice is lighter, and so the seat tends to wear a little less over time.
Balanced 2nd stages are designed so that fluctuations in IP do not affect the breathing resistance as much as with unbalanced 2nds; they are held closed by much lighter springs, and some of the downstream air pressure from the 1st stage is contained in a chamber and assists in keeping the valve closed. One advantage of balanced 2nds is that when they are not being used, the spring pressure on the orifice is lighter, and so the seat tends to wear a little less over time.
