Balanced both 1st and 2nd stages less safe?

[ericpitar]

ouch! I'm getting paddled by the seniors.....hehehe. I do regularly check my SPG in fact, but I thought an extra redundancy in warning could be useful. From reading the posts above, it sounds like the extra "redundancy" in warning wouldn't be significantly more, if any, with a balanced *1st* stage and unbalanced 2nd stage, correct? (i.e. if i was really that stubborn in creating a redundant warning system, it should be unbalanced 1st and 2nd)

Thank you all! I am learning so much here!

e

 

[DA Aquamaster]

With a balanced first stage the intermediate pressure is very stable.

Since it is the intermediate pressure that has an impact on changes in the inhalation effort of the second stage, if the IP does not change, neither does the inhalation effort, regardless of whether the second stage is balanced or not. So in effect, with a good balanced first stage like the Mk 25 you will not notice any increase in inhalation effort until the tank pressure falls to the IP pressure - about 120-140 psi. There is not very much air left in the tank at that pressure

With an unbalanced fisrt stage it is not uncommon to see a drop in IP on the order of 15-20 psi as the tank pressure falls from 3000 psi to 300 psi. This will have a noticeable impact on an unbalanced second stage and in fact will have an impact on inhalation effort even with a balanced second stage as a balanced downstream second stage must still have a donwnstream bias to prevent damage in the event of excessivly high IP. The effect is greatly reduced but would still be noticeable at low tank pressures in the 200-300 psi range.

Some unbalanced first stages can be very finely tuned and offer excellent inhalation efforts when attached to a balanced first stage.

 

[Couv]

ouch! I'm getting paddled by the seniors.....hehehe. I do regularly check my SPG in fact, but I thought an extra redundancy in warning could be useful. From reading the posts above, it sounds like the extra "redundancy" in warning wouldn't be significantly more, if any, with a balanced *1st* stage and unbalanced 2nd stage, correct? (i.e. if i was really that stubborn in creating a redundant warning system, it should be unbalanced 1st and 2nd)

Thank you all! I am learning so much here!

e

Boy have I got the reg for you. The SP MK VII "Honker" When the tank pressure gets low...HONK HONK....

But to answer your question; Yes, to get the effect you are asking for the best combination would be an unbalanced first stage (only comes in piston) and an unbalanced second stage,

(Edit: I should have read DA post above, he gives a great explanation as to why)

... preferably with an adjustment knob. When you find yourself reaching to adjust the inhalation resistance, that serves a a clue to check your tank pressure.

I am going to take a rare step go against my fellow "Usual Suspects" here with this side note, I too used a J valve with no problems for years. The policy of the first club I belonged was to have a SPG or a J valve. I never had one accidentally knocked off reserve so that was never an issue. When I think back on those days, one thing that was probably to my advantage was that my consumption rate tended to be lower than most of my buddies. Later, when I was doing body recovery in dark water with mud and junk on the bottom removing the SPG and hose made sense.

c