Can a regulator breathe too easily?
Yes, it definitely can.
Today, Christine and I went diving at Kettle Cove in Cape Elizabeth, Maine. The water temperature was adequate for diving wet, but we were both testing new stuff in our dry suit. I had a new neck seal and Christine was trying basically a new dry suit.
In addition, I was testing a Phoenix HPR with a new diaphragm. By just swapping the diaphragm, on the bench this regulator was showing a consistent and stable cracking effort of 0.3 inWC. I new that this was too low, for the cracking effort, but I just didn’t want to detune at this point. Well, that was a mistake.
First, both Christine and my dry-suit worked great.
The regulator breathed great in the swimming position, but every time I got on a vertical position it free flowed out of the exhaust due to the low cracking effort. The duckbill eliminator is centered right in front of the diaphragm. But, the valve is 1 inch in diameter.
That means the radius is 0.5 inches. Since the cracking effort is only 0.3 inWC, than means that the top edge of the valve in the DBE is 0.2 in higher in the water column than the center of the diaphragm when I am in the vertical position. This translates into a very predictable free flow when I am in a vertical position.
Well, normally this would not have been a problem in the normal swimming position, and that is why I didn’t bother to adjust the regulator before the dive.
With a dry-suit and a long shallow water (8 to 10 ft) swim back to shore… it is a problem. In shallow water it is much easier to squeeze the air out of the legs and vent by tilting slightly vertical. But every time I did that, I wasted a lot of air. A couple of times I saw my pressure gauge just drop 100 psi like nothing… that long shallow water swim was getting annoyingly longer. In a dive like this, I do carry a snorkel, but I don’t particularly like using it.
Anyway, this is an easy fix. There is absolutely no reason to have a regulator tuned to that low level. A 0.2 inWC difference in cracking suction can only be measure by a calibrated instrument… it is not something one can normally perceive.
Note: most modern single hose regulator have to be adjusted to a cracking effort of not less than 0.8 to 1.0 inWC (most to more than 1.0 inWC), due to case fault geometry. Case fault geometry it the term used to describe the distance from the exhaust to the diaphragm in a single hose regulator. In a diver inverted position, that distance will cause a free flow out the exhaust if the regulator is tuned too sensitive.