_Slacker_
Contributor
Your metabolic rate does not vary with depth. Why would you want your O2 addition to vary with depth?
SF2 or REvo rebreathers
- Thread starter JonnyQuest
- Start date
Please register or login
Welcome to ScubaBoard, the world's largest scuba diving community. Registration is not required to read the forums, but we encourage you to join. Joining has its benefits and enables you to participate in the discussions.
Benefits of registering include
- Ability to post and comment on topics and discussions.
- A Free photo gallery to share your dive photos with the world.
- You can make this box go away
I'm not missing the physics of what's going on, I just don't see a point in introducing another variable in what you're controlling. Especially since simplicity is the goal with the Fathom. You've gotta adjust the needle valve either way since you're adjusting the orifice size no matter what. It's really not difficult to spin a needle valve. It's literally as complicated as hitting an O2 MAV addition button. The "additional fiddling" aspect is just really overstated, even with a light and a reel and a scooter. It's just not a deal at all. It's about as task loading as switching your light from your left hand to your right hand to scratch an itch through your hood.
Since just a blocked first stage doesn't allow you to compensate for changes in metabolic rate, you're changing your O2 addition profile anyway, so whether that's by opening or closing a needle valve, or manually pressing a button, you're still doing something. Once you've got a few dives on a needle valve and can pretty well open or close it to do what you want re: your metabolic rate, you're actually decreasing the amount of task loading going on during period of work, since you've already compensated by changing the amount of flow. Since you're doing it anyway, 1/4 turn is no more intensive than 1/2 a turn. It's like valves on a garden hose. Why regulate at the tap when you've got a nozzle you're gonna use anyway?
As far as swapping out regs, let's say you've gone from using a blocked first stage to an unblocked first stage, now you're adding additional task loading because you're introducing another variable that you haven't been accounting for prior. You're adding in an inconsistency. The right answer is to swap out first stages with another blocked first stage with the same IP. Not everyone is going to have the ability to do that all the time. Can those guys handle it with no issue? Sure, but why would they want to, especially on a big dive. Not everyone buying a Fathom is gonna be those guys pushing miles into a cave.
Like I said, I don't get why you'd want to have both. I have yet to experience an issue where a needle valve on an unblocked first stage has ever been too much to handle or caused any grief whatsoever. It's just not that big a deal to spin it open or spin in closed, even with a bunch of other stuff going on. I get that those guys want it different. They're doing some awesome dives with their units. That's cool. That has little bearing on the dives I'm doing. Clearly they appreciate that setup. That I disagree isn't a reflection on them or their practices. It just doesn't make sense for me. There are so many other considerations going on that the spinning of a needle valve is the furthest thing from my mind on something like a 4-6 hour dive. And considering the dives that a bunch of guys are doing on a bunch of different rebreathers, there's clearly more than one way to skin that cat. Use what works for you.
Since just a blocked first stage doesn't allow you to compensate for changes in metabolic rate, you're changing your O2 addition profile anyway, so whether that's by opening or closing a needle valve, or manually pressing a button, you're still doing something. Once you've got a few dives on a needle valve and can pretty well open or close it to do what you want re: your metabolic rate, you're actually decreasing the amount of task loading going on during period of work, since you've already compensated by changing the amount of flow. Since you're doing it anyway, 1/4 turn is no more intensive than 1/2 a turn. It's like valves on a garden hose. Why regulate at the tap when you've got a nozzle you're gonna use anyway?
As far as swapping out regs, let's say you've gone from using a blocked first stage to an unblocked first stage, now you're adding additional task loading because you're introducing another variable that you haven't been accounting for prior. You're adding in an inconsistency. The right answer is to swap out first stages with another blocked first stage with the same IP. Not everyone is going to have the ability to do that all the time. Can those guys handle it with no issue? Sure, but why would they want to, especially on a big dive. Not everyone buying a Fathom is gonna be those guys pushing miles into a cave.
Like I said, I don't get why you'd want to have both. I have yet to experience an issue where a needle valve on an unblocked first stage has ever been too much to handle or caused any grief whatsoever. It's just not that big a deal to spin it open or spin in closed, even with a bunch of other stuff going on. I get that those guys want it different. They're doing some awesome dives with their units. That's cool. That has little bearing on the dives I'm doing. Clearly they appreciate that setup. That I disagree isn't a reflection on them or their practices. It just doesn't make sense for me. There are so many other considerations going on that the spinning of a needle valve is the furthest thing from my mind on something like a 4-6 hour dive. And considering the dives that a bunch of guys are doing on a bunch of different rebreathers, there's clearly more than one way to skin that cat. Use what works for you.
Similar threads
