One of the most commonly mentioned regulator terms is “balanced.” This term is often misunderstood and sometimes misused by salesmen, so this article will hopefully clear things up. Take a deep breath (no pun intended) and I’ll explain exactly what the term means for regulator performance.
What Is a Balanced Regulator?
Simply put, a regulator first stage or second stage is “balanced” when it does not react significantly to changes in the air pressure supplying it. This means that balanced first stages put out the same intermediate pressure (IP) regardless of the air pressure in the tank, and that balanced second stages initiate air flow to the diver with the same effort even if the IP fluctuates. So how is this accomplished?
Balanced First Stages:
Balanced first stages supply air at a constant intermediate pressure (IP), regardless of the pressure remaining in a scuba diver’s tank. This is important because first stages must function with a very wide range of tank pressures, such as 3000 psi in a full tank to under 500 psi as a diver depletes his air supply.
The way this is achieved varies between diaphragm and piston first stages, but in both types of first stages, balancing means that the air pressure from the tank does not influence the amount of force needed to close the high pressure valve inside the first stage. This amount of force is what determines intermediate pressure. (IP)
With unbalanced piston first stages, the air from the tank pushes on the valve, adding to the amount of force required to close the valve. As the tank empties, there is less force pushing on the valve, and less force is needed to close the valve. Remember that in first stages, air pressure builds up in the second chamber until it reaches IP and closes the valve, cutting off air from the tank. So less force needed to close the valve translates into lower IP. All current diaphragm first stages are balanced.
Balanced Second Stages:
All second stages use a spring to keep the valve closed until a diver inhales. Air pressure from the hose (from the first stage), or IP, is pushing against this spring, trying to force the valve open. Balanced second stages take some of this IP air and divert it to a chamber where it can “push back” against the pressure from the first stage.
In a balanced second stage, a much lighter spring can be used to hold the valve closed with very little pressure, because the diverted air is supplying most of the force. This means that as IP (the force trying to open the valve) changes, so does the force trying keep it closed, resulting in little change in forces on the valve. Unbalanced second stages use a heavier mechanical spring that is set to match a specific IP, so when the IP changes (usually drops) the valve is a little harder to open, meaning increased breathing effort.
What Are the Benefits of a Balanced Regulator?
When using an unbalanced first and second stage regulator, breathing resistance increases slightly as a diver’s tank pressure drops. The key word here is slightly. Balanced first stages will supply a steady IP to the second stage until the tank pressure goes below the IP. At this point, the tank is just about empty.
Manufacturers and dealers often tout this as a benefit of balanced regulators, correctly claiming that they breathe the same regardless of the tank pressure. However, for some divers there might be an advantage to a bit of warning as the tank nears empty. In fact, some older regulators and tank valves incorporated deliberate increases in breathing resistance as the tank emptied so that divers in the pre-pressure-gauge era would have ample warning that they were about to run out of air. Some diving practices have really changed! Balanced second stages have some subtle benefits; one is that they might last a little longer between servicing because the spring pressure on the seat is lower.
Depth Compensation Is Not Balancing!
A common claim about balanced regulators is that they perform equally well at depth, implying that unbalanced regulators are suitable for only shallow dives. This is not true! All regulators compensate for depth in the same way, by using the ambient water pressure surrounding the diver to adjust the IP and pressure inside the second stage. For example, let’s say we have a first stage set to produce an IP of 135 PSI on the surface. At 66 ft the ambient pressure is approximately 2 atm or 30 PSI greater than at the surface. By exposing part of the first stage to this pressure, the IP is automatically adjusted to 165 PSI, or a steady 135 PSI above the ambient pressure. All first stages do this, otherwise they would not work for scuba diving.
Some regulators are sold as ‘over-balanced’, meaning that they are designed to increase IP as depth increases even more than the change in ambient pressure. This would be better called “over-depth-compensating” but that doesn’t have the same sales ring! This feature does little to increase performance at depth; in fact, since all of these regulators are sold with balanced second stages, the increase in IP at depth is simply compensated for by the second stage, essentially negating any performance benefit.
Should You Buy a Balanced Regulator?
While balancing does have some advantages, the bottom line is that unbalanced regulators can be very high quality and perform very well in recreational diving. Remember, just a few decades ago Jacques Cousteau and other ground-breaking scuba divers routinely made very deep, very demanding dives on unbalanced regulators. Try to keep that in mind when a salesman tells you that only the high-end models he sells are good enough!