First stage IP and dive below 100m

[exposure]

Hello,

If I am not wrong our standard first stage give an intermediate pressure of 10bar to the second stage. I’d like to understand what happen when you reach 100m or deeper so that the IP is below the ambiant pressure. Any reference to articles would be great as well.

Yvan

 

[berndo]

It's 10 bar over ambient pressure. First stages are depth compensated, otherwise your second stage wouldn't work even 1m down.
So it's 11 bar at 10m, 12 bar at 20m, 13 bar at 30m and so on.

 

[exposure]

Thanks for your very quick answer.

 

[GF99/99]

Unless you have a plugged first stage. Like a DS4 or similar variant/copy. Then yes your correct it will stop working at the depth equivalent pressure the IP is at.

But if your plugging a 1st stage then you obviously have a very special application like for a CMF and you know the implications. But just something to think about if you like me I have a couple plugged DS4’s in my pile of Apeks 1st stages so its something to be aware of.

 

[divingx]

Most first stages are depth compensating. That means the IP will remain constant, in your case 10 bar above ambient pressure. The mechanics are pretty simple. For example, a sealed diaphragm regulator has a rubber environment seal, which will push in when there’s a greater ambient pressure. Then the rubber will push the plastic seat underneath it and cause an increase in IP. The IP of some over compensating first stage like Apeks actually increases faster than the ambient pressure when you go down.

Edit: Delete the last paragraph as it's confusing.

 

[berndo]

Most first stages are depth compensating. That means the IP will remain constant, in your case 10 bar above ambient pressure.

What first stage isn't compensated? Plugged stages aren't sold by any manufacturer and can't be run with a second stage. The plugged DS4s GF99 mentioned are modified with aftermarked parts for mCCR only.
I think the OP was asking about normal 1. stages.

The IP of some over compensating first stage like Apeks actually increase faster than the ambient pressure when you go down.

Huh? If the IP rises more than standard IP plus ambient, you'll end up with a free flow.

Unless you remove block the first stage by something like this Fathom Fixed IP Cap for a MCCR, the IP shouldn’t be a issue until doing deeper than 200 metres. Some regs will start to drop IP sooner/quicker than the others. IRCC DS4 will drop earlier and faster than MK17 evo.

I don't understand what you're trying to say. In a plugged first stage, the type of spring determines the IP and the max depth.

The OP's question was pretty straight forward... you're making it more complicated and confusing, imho.

 

[divingx]

Huh? If the IP rises more than standard IP plus ambient, you'll end up with a free flow.

Apeks first stages are over-balanced - Unique over-balanced, diaphragm design - as the diver descends, the over-balancing feature allows the medium pressure gas in the hose to increase at a rate faster than ambient. This results in superior performance at depth.

I don't understand what you're trying to say. In a plugged first stage, the type of spring determines the IP and the max depth.

The OP's question was pretty straight forward... you're making it more complicated and confusing, imho.

Deleted this part as it is confusing. Wasn't awake when I typed this lol. Just trying to say IP could start to drop at depth. Find these diagrams on the forum. Not sure of the source though.

 

[exposure]

Thanks all for your great answers. I think I was confused with the DS4 used on Revo. Thanks again.

 

[evandroairton]

Used Scubapro MK2 as both diluent and O2 on my inspo 85 meters plus dives. No complains
The Wing inflator would be slower but not a major concern on CCR.
Anyway, on OC, poseidon and the MK25 would be my choice, followed by apeks and its "clones"