Minimal Acceptable Ending Tank PSI

[redacted]

The OP is shore diving when doing this and was wondering if dive/fill shops would want the tanks to come back with some gas remaining.

My understanding is that boat Captains make the rules. If he/she says, "Be back on the boat with x amount of gas," that is their right to enforce that rule. It is also a diver's right to take their business where they wish or buy their own boat.

While the op may be able to stop you from diving, unless the rule was established before the contract was entered, I expect there will be an appropriate refund.

 

[TMHeimer]

While the op may be able to stop you from diving, unless the rule was established before the contract was entered, I expect there will be an appropriate refund.

Agree. I also have heard the boat "must have 500 or you're done" rule, but never saw anyone actually check people.

 

[EricTheDood]

I'll fight that one. Cubic footage is different in the hose VS in the tank.
You can't empty a 3000psi Al 80 in 4 breaths like you can on a 3000psi filled reg set.
200psi tank open is different from 200psi tank closed.

Not sure I follow the logic here. The issue isn't the volume of gas. It's strictly the pressure.

Like @BRT said, when the actual tank pressure dips below the first stage set point, the first stage is basically wide open.

A regulator is a pressure limiter. It has a MAX set point but doesn't have a MIN set point. In other words, any pressure higher than the IP set point will get reduced, but anything lower will be unrestricted.

 

[MXGratefulDiver]

... there's also the fact that you may not have as much gas left in that tank as you think you have ... SPG's are notoriously inaccurate ...

... Bob (Grateful Diver)

 

[g1138]

Not sure I follow the logic here. The issue isn't the volume of gas. It's strictly the pressure.

Like @BRT said, when the actual tank pressure dips below the first stage set point, the first stage is basically wide open.

A regulator is a pressure limiter. It has a MAX set point but doesn't have a MIN set point. In other words, any pressure higher than the IP set point will get reduced, but anything lower will be unrestricted.

I didn't catch his example as relevant until after he explained it in the follow up reply.
Calling the air pull as "dry" after your usable psi in my original post was my lazy way of saying till you reach the point of having to pull air through the reg VS it feeding it to you. And it was taken literal.

Then with BRT's example I didn't catch the reference of purging air past the point of IP pressure because he's taking my post as literal. Pulling pressure out of a hose where your cf & pressure is dropping immensely (tank closed) VS pulling where your tank pressure and cf aren't dropping quickly (tank open) is different. But I wasn't understanding that he was just referencing just the fact that you can bleed your reg past IP pressure.

I think the point has been clarified for me.