does interstage pressure really matter ?

[Scuba Steve]

im thinking of getting apex tek first stage regs . and just wondering i have scuba pro octos , will they work with the apex and whats the interstage pressure or does it really matter .

[nigelH]

They are close enough not to matter. I think it's only some Posideons that are very different but even that just means they are not 'optimum'.

Naturally one manufacturer does not test their gear with anybody else's so you get the usual 'we cannot recommend it' rubbish.

[incapete]

If you've got an IP guage then couldn't you adjust the first stage to match the output required by the second stage?

[NotDeadYet]

I think it's only some Posideons that are very different but even that just means they are not 'optimum'.

Depends on the reg, on the Cyklone it doesn't make a huge difference but the Jetstream needs a certain IP in order to close the valve. You see it if you ever breathe a cylinder dry on a Jetstream, when the cylinder pressure drops below the IP then the 2nd stage goes into freeflow. Dumping the last of your gas just when you need it... who says Scandinavians have no sense of humour

[iain/hsm]

Originally Posted by Scuba Steve

im thinking of getting apex tek first stage regs . and just wondering i have scuba pro octos , will they work with the apex and whats the interstage pressure or does it really matter .

Inter stage pressure is critical. The demand regulator needs the inter stage “drive” pressure to balance the spring holding the pressure back on the second stage seat. The diaphragm, lever fulcrum point gives some advantage to inhalation effort but again it is only balanced within a fine pressure range to spring tension. Too little and your work of breathing (WOB) and inhalation effort increases so its like your breathing through a straw. Too much and your in free flow.

Two other things happen, first to get flow you need a pressure drop, second as the bottle pressure decreases the inter stage pressure increases. So the balance between the spring rate and the contact area of the LP seat and the drive pressure are critical in balancing the design. So changing the inter stage pressure is IMHO critical.

My other point is when you try selling your two mixed brands on E-bay when your done and see just how much your rig is worth as a mixed set then. Just a thought.

[Digger]

Originally Posted by iain/hsm

Inter stage pressure is critical. The demand regulator needs the inter stage “drive” pressure to balance the spring holding the pressure back on the second stage seat. The diaphragm, lever fulcrum point gives some advantage to inhalation effort but again it is only balanced within a fine pressure range to spring tension. Too little and your work of breathing (WOB) and inhalation effort increases so its like your breathing through a straw. Too much and your in free flow.

Two other things happen, first to get flow you need a pressure drop, second as the bottle pressure decreases the inter stage pressure increases. So the balance between the spring rate and the contact area of the LP seat and the drive pressure are critical in balancing the design. So changing the inter stage pressure is IMHO critical.

My other point is when you try selling your two mixed brands on E-bay when your done and see just how much your rig is worth as a mixed set then. Just a thought.

All this said, a Scubapro and Apeks first and second stage work perfectly fine straight out of the box and just screwed into each other. I know, because I've done it dozens of times and it's fine.

Most first stages aren't accurate enough on the IP that you'd be able to adjust them precisely between the 9 bar IP and 9.2 bar IP that one or the other needs, so trying to tweak one to match the other is a bit pointless, and you'll never feel the difference.

If you put a Poseidon on an Apeks first stage or vice versa, then yes you will tell the difference, but not between Apeks, Scubapro, Mares, and just about every other normal reg on the market. Most of them are the same design and same technology, and a fair number come from the same factory anyhow.

Digs.

[Scuba Steve]

who said anything bout selling them . im thinkin of buyin the apex tek . thats all and have a few scubapro regs lyin around tat all

[NotDeadYet]

Originally Posted by Digger

If you put a Poseidon on an Apeks first stage or vice versa, then yes you will tell the difference, but not between Apeks, Scubapro, Mares, and just about every other normal reg on the market. Most of them are the same design and same technology, and a fair number come from the same factory anyhow.

Scubapro second stages on Poseidon 1st stages used to be a very common set up for trimix diving. It worked very well.