Balanced both 1st and 2nd stages less safe?

[ericpitar]

Hello all,

Am i correct in thinking that safetywise, I'm better off having an unbalanced 2nd stage if I have a balanced 1st stage? Otherwise, having a balanced 1st *and* 2nd stage would give me no warning when the air is running low. That is, if both 1st and 2nd are balanced, it'll be one inhale(or half?) and I'll be out of air without warning if I've been distracted enough not to check my spg? On the other hand, having balanced 1st but *unbalanced* 2nd wouild give me some warning when air is running low by way of increased breathing resistance. Am i correct?

Set up is MK25/R190.

e

 

[Jimmer]

Well you should NEVER be using breathing resistance as an indicator of running low. Most unbalanced regs need to be quite low before the resistance gets very high, at which rate you'd be in heaps of trouble if you were deep. You should be using proper gas planning and following the plan including regular checks of your SPG.

Secondly, the first stage is the part that dictates most of the breathing resistance with low supply pressure. So if you have a balanced piston Mk25 with an unblanced R190, it would likely still breathe evenly the whole time. Remember the second stage only deals with what pressure the first delivers to it. So if the first stage is balanced and delivering a consistent pressure to the second stage, you'd never notice anyway.

 

[Gil57usa]

That is, if both 1st and 2nd are balanced, it'll be one inhale(or half?) and I'll be out of air without warning if I've been distracted enough not to check my spg?
Set up is MK25/R190.

e

I would strongly suggest that you make it a priority to develop the habit of checking your SPG regularly. There is absolutely no excuse for running that low on air without being aware of it. On the other hand, we may get to see another example of Darwin in action.

 

[Luis H]

To get any hard to breath warning, both the first and the second stage need to be unbalanced.

If either the first or the second are balanced you will probably not notice any difference in breathing at any tank pressure.

A decent balanced first stage will provide an IP constant enough that will not change the performance of the second stage, even if the second stage in not pneumatically balanced.

The performance of a pneumatically balanced second stage is not affected as much by changes in intermediate pressure (IP). Therefore even if you pair an unbalanced first stage with a pneumatically balanced second stage, you will probably not notice that the IP is changing some with changing tank pressure.


Added:
In your particular example, the MK-25 will have a very constant IP at any tank pressure. It will give you no indication of tank pressure change.


Edit: I missed a "not" when typing. Thanks Herman for pointing it out.

 

[Web Monkey]

Am i correct in thinking that safetywise, I'm better off having an unbalanced 2nd stage if I have a balanced 1st stage? Otherwise, having a balanced 1st *and* 2nd stage would give me no warning when the air is running low. That is, if both 1st and 2nd are balanced, it'll be one inhale(or half?) and I'll be out of air without warning if I've been distracted enough not to check my spg?

The fix? Don't be distracted!

There is nothing going on underwater that more important than watching your remaining gas and your depth.

It doesn't matter if you just found the Lost City of Atlantis. It won't make any difference if you're dead.

Terry

 

[Luis H]

I would strongly suggest that you make it a priority to develop the habit of checking your SPG regularly. There is absolutely no excuse for running that low on air without being aware of it. On the other hand, we may get to see another example of Darwin in action.

I am a strong believer on SPG…I was one of the first in my group that regularly used one…but not always. On the other hand I never saw anyone who died from not having an SPG. I am not sure where that rumor started.

The law of natural selection is not going to be offset by any single piece of equipment.

 

[Luis H]

The fix? Don't be distracted!

There is nothing going on underwater that more important than watching your remaining gas and your depth.

It doesn't matter if you just found the Lost City of Atlantis. It won't make any difference if you're dead.

Terry

Did you never see Thunderball?
What if you need to fight one of Emilio Largo’s henchmen?

 

[herman]

Did you never see Thunderball?
What if you need to fight one of Emilio Largo’s henchmen?

It does happen...Rob had to deal with a leftover one at Sand Dog this year.

 

[DA Aquamaster]

I startd diving in the late 1970's (and got certified in 1985 so read between the lines on that one...) and being very cash strapped skipped the SPG and used tanks with J-valves along with an unbalanced Mk 3 R108 until around 1986 or so.

Luis is correct that a Mk 5 will give you no warning as the Ip is very stable. The Mk 3 worked well as an early warning device as it was unbalanced and used a fairly small diameter piston head which gave it a very large change in IP from full to empty tank pressures. But...you still had to be pretty well attuned to your regulator, which in turn had to be very finely tuned and then you still had to concentrate on noticing the difference.

J-valves worked less well as it was not uncommon for the valve to get pulled during the dive, leaving you with an empty tank when you exected to have a reserve.

That said, one of the major reasons I never got in trouble was that most of my diving was drift diving in rivers at depths of 30' or less, so an ascent to the surface was not difficult if you found yourself with a hard breathing reg with only a few breaths left in the tank.

 

[texdiveguy]

J-valves worked less well as it was not uncommon for the valve to get pulled during the dive, leaving you with an empty tank when you exected to have a reserve.

I dove J-valves for years and never experienced a 'pull down' during a dive that was accidental...lucky--careful...I would say it was uncommon to have that occur.