Scuba
Contributor
A summary of my understanding of the H-valve.
What an H-valve does is provide redundancy of regulator stages, hoses, and o-rings in the event one should fail. It provides redundancy of the gas delivery system with the exception of tank valve connection at gas source.
A regulator can critically fail in two ways. Free flow which cant be stopped and complete gas supply shutoff.
Free flow is the most common one by far. As pointed out it occurs most often, but not exclusively, in cold waters. Using a properly maintained good quality regulator with cold water kit if required and following cold water regulator protocol can greatly reduce the risk, but not eliminate it.
Complete gas supply shutoff appears to be very rare. Nevertheless, this is a matter of critical urgency. Improper service seems to be the biggest culprit here, based on what I have read and heard. Find a good technician or learn to do it very well yourself, and test the regulator after servicing. I do a few easy shallow dives with a redundant gas supply or buddy, since most problems will arise soon after improper service is performed. I put it through its paces, normal breathing, rapid, simultaneous octo/backup reg use, along with physically turning in every position. Vertical, horizontal, diagonal rotations. Too much? Oh well.
You also have the more common problems of o-rings, hose blowouts and quickly remedied freeflows.
The H-valve provides redundancy for all of these, assuming - you become competent in its operation. The downside to it is the addition of components which can malfunction, o-ring (s) and first stage, and an increase in operational complexity due to multiple valves. These negatives can be effectively managed through diligent checks, proper maintenance and good training, resulting in a net positive gain.
What the H-valve does not do is provide redundancy for tank valve failure where it connects to gas source. This is a very rare event that can completely shutoff gas supply. The valve orifice could become blocked, due to part breakage (I believe I heard or read this someplace) or more commonly loose matter inside tank. Flaking of tank wall due to corrosion. This loose matter is possibly more likely to shutoff or severely restrict gas flow by clogging the regulator first stage filter. (inside of regulator?) H-valve offers some protection here as both first stage regulators would have to be clogged to completely stop all gas flow. (Bare in mind that these are rare events which are difficult to correctly diagnose, and difficult to precisely calculate statistically. Meaning, the exact cause is often attributed through an educated assumption and expected occurrence is unknown.
Maintenance is once again of critical importance here. Reducing the risk to almost nil.
And it goes without saying, the H-valve does not provide for a redundant gas source.
This is the story of the H valve as I see it. Others are welcome to add or subtract. It is designed to reduce the risk of gas loss due to gas delivery system malfunction. It covers all the bases with the one aforementioned notable exception.
Optik, I am not an instructor. Nor a diver with decades of practice. Nor a diver with thousands of dives. I am just a diver learning to dive safely, just like you. I would not stop the analysis here with the gas delivery system, but consider the gas supply source as well for solo diving. For anything but extremely shallow dives under good conditions. Even then, I would still scrutinize this aspect, in order to gain a broad understanding of the subject, allowing me to make a decision to my satisfaction.
What an H-valve does is provide redundancy of regulator stages, hoses, and o-rings in the event one should fail. It provides redundancy of the gas delivery system with the exception of tank valve connection at gas source.
A regulator can critically fail in two ways. Free flow which cant be stopped and complete gas supply shutoff.
Free flow is the most common one by far. As pointed out it occurs most often, but not exclusively, in cold waters. Using a properly maintained good quality regulator with cold water kit if required and following cold water regulator protocol can greatly reduce the risk, but not eliminate it.
Complete gas supply shutoff appears to be very rare. Nevertheless, this is a matter of critical urgency. Improper service seems to be the biggest culprit here, based on what I have read and heard. Find a good technician or learn to do it very well yourself, and test the regulator after servicing. I do a few easy shallow dives with a redundant gas supply or buddy, since most problems will arise soon after improper service is performed. I put it through its paces, normal breathing, rapid, simultaneous octo/backup reg use, along with physically turning in every position. Vertical, horizontal, diagonal rotations. Too much? Oh well.
You also have the more common problems of o-rings, hose blowouts and quickly remedied freeflows.
The H-valve provides redundancy for all of these, assuming - you become competent in its operation. The downside to it is the addition of components which can malfunction, o-ring (s) and first stage, and an increase in operational complexity due to multiple valves. These negatives can be effectively managed through diligent checks, proper maintenance and good training, resulting in a net positive gain.
What the H-valve does not do is provide redundancy for tank valve failure where it connects to gas source. This is a very rare event that can completely shutoff gas supply. The valve orifice could become blocked, due to part breakage (I believe I heard or read this someplace) or more commonly loose matter inside tank. Flaking of tank wall due to corrosion. This loose matter is possibly more likely to shutoff or severely restrict gas flow by clogging the regulator first stage filter. (inside of regulator?) H-valve offers some protection here as both first stage regulators would have to be clogged to completely stop all gas flow. (Bare in mind that these are rare events which are difficult to correctly diagnose, and difficult to precisely calculate statistically. Meaning, the exact cause is often attributed through an educated assumption and expected occurrence is unknown.
Maintenance is once again of critical importance here. Reducing the risk to almost nil.
And it goes without saying, the H-valve does not provide for a redundant gas source.
This is the story of the H valve as I see it. Others are welcome to add or subtract. It is designed to reduce the risk of gas loss due to gas delivery system malfunction. It covers all the bases with the one aforementioned notable exception.
Optik, I am not an instructor. Nor a diver with decades of practice. Nor a diver with thousands of dives. I am just a diver learning to dive safely, just like you. I would not stop the analysis here with the gas delivery system, but consider the gas supply source as well for solo diving. For anything but extremely shallow dives under good conditions. Even then, I would still scrutinize this aspect, in order to gain a broad understanding of the subject, allowing me to make a decision to my satisfaction.
