HP drop on inhalation

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Gyula Fora

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Messages
34
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Location
Sweden
# of dives
100 - 199
Hi all!

Yesterday I used a slightly older Apeks reg and I noticed that the HP gauge dipped considerably every time I inhaled.

I double checked that the tank was completely open and the reg seemed to give enough air as far as I could tell.

Is this normal with some first stage designs?

Thanks!
 
Typically a first stage will show a dynamic drop of 8-20 psi on purge/max flow. On inhalation, it is usually much less.
An IP drop indicates inadequate tank gas getting to the first stage, or markedly increased internal friction from a HP oring, perhaps.

If the tank valve was wide open (or on two tanks, to rule out a valve problem), then I would think either a very blocked sintered metal filter where tank air first enters (like from grease or verdigris corrosion from salt water), or a component about to fail.

Lol, tbone beat me to it!
 
Hi all!

Yesterday I used a slightly older Apeks reg and I noticed that the HP gauge dipped considerably every time I inhaled.

I double checked that the tank was completely open and the reg seemed to give enough air as far as I could tell.

Is this normal with some first stage designs?

Thanks!

No it's not normal. It's probably not a regulator issue unless (I guess) it could be a clogged filter. Try a different tank, then if you are able to remove the filter for testing it, try it without the filter. If it still does it I'm stumped.
 
Thanks guys for the info, I will try it on a different tank and see what happens! I will post the outcome
 
Not likely I know but I'll throw it out there just in case. That is normal if you are using a J valve in the dive position. I see it fairly often but then I often use vintage tanks with operable J valves a lot of the time. Otherwise, I agree with the above.
 
Not likely I know but I'll throw it out there just in case. That is normal if you are using a J valve in the dive position. I see it fairly often but then I often use vintage tanks with operable J valves a lot of the time. Otherwise, I agree with the above.

That is exactly what I was using, it’s a very old tank/valve. So it could be a valve problem then, interesting. Why would it happen with the J valves?
 
Dang, that was your issue. :)
That is NORMAL for a properly working J valve in the dive position. When in the dive position, the valve has a seat that closes under spring pressure and is opened by the differential pressure when you breath. There is always some pressure drop across that seat, the amount depends on what the tank pressure is and the design of the valve. At some point, usually around 300-500 psi breathing will become difficult by design, which was your warning to end the dive. In the early days of diving there were no SPG's so this was you low pressure warning. If you set the tank to reserve (down position if it's set up correctly) it should not show a pressure drop if it's working properly. This may help.
I dive vintage tanks and use these valves fairly often so it's something I see more than most people, Couv may have to be removed from the vintage dive community for missing this. :) Dive the tank in the down position with modern regs and you will be fine.....or dive it as intended, ignore the SPG swings and see how it works to warn you of low air when your tank gets low.
 
Dang, that was your issue. :)
That is NORMAL for a properly working J valve in the dive position. When in the dive position, the valve has a seat that closes under spring pressure and is opened by the differential pressure when you breath. There is always some pressure drop across that seat, the amount depends on what the tank pressure is and the design of the valve. At some point, usually around 300-500 psi breathing will become difficult by design, which was your warning to end the dive. In the early days of diving there were no SPG's so this was you low pressure warning. If you set the tank to reserve (down position if it's set up correctly) it should not show a pressure drop if it's working properly. This may help.
I dive vintage tanks and use these valves fairly often so it's something I see more than most people, Couv may have to be removed from the vintage dive community for missing this. :) Dive the tank in the down position with modern regs and you will be fine.....or dive it as intended, ignore the SPG swings and see how it works to warn you of low air when your tank gets low.

Thanks a lot, this is pretty sweet info, highly appreciated!

It’s always nice to learn how the the designs have evolved over time to meet the requirements.
 
https://www.shearwater.com/products/teric/

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