- Reaction score
- Hillsborough, NC
- # of dives
- 500 - 999
So you are saying that the intermediate pressure measured relative to the ambient pressure will be dropping with depth?
The delta from the IP to the ambient pressure will decrease with depth, yes. However it isn't because the IP is decreasing, it is only because the ambient pressure is increasing.
The intermediate pressure delivered by a balanced 1st stage regulator doesn't change unless the tank pressure drops so low that you are OOG. In an unbalanced 1st stage the IP drops during the dive as your tank pressure drops, but not because of depth.
This is the whole reason for balanced 1st stages.
A better way to think of it is to say that with depth...the ambient pressure increases but the IP remains the same (in a balanced 1st stage). So, in an unbalanced 2nd stage it gets slightly more difficult to breath as you go deeper since the ambient pressure resists the 2nd stage opening more as you go deeper. In order to breath you have to overcome the 2nd stage spring pressure( Also called cracking pressure or inhalation effort) plus the increase in ambient pressure. Also, the delta here between the IP and Ambient pressure does affect the actual airflow delivered to you. The larger the delta the faster the air flows through the hose and into you. So, the deeper you are the more you have to suck to get the same air volume.
Many regulator manufacturers add a venturi assist to their second stages to counteract some of these effects. Some of these venturi assists are slightly adjustable by the diver with +/- levers. Not the knobs on higher end user adjustable regulators, that's a different aspect all together and I am already starting to ramble...
In a Balanced 2nd stage, the increasing ambient pressure is accounted for so you only have to overcome the spring pressure regardless of depth.
This is the whole reason for balanced 2nd stages
This is essentially the marketing version of what is happening, when I want to sell you a balanced 2nd stage regulator. It's accurate enough for this discussion.
Generally speaking, most people don't really feel the difference for shallow dives. Once you start going deeper and have been diving for a while then it starts to matter more.