Pneumatically Balanced 2nd Really True???

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FFMDiver

FFMDiver

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I'm thinking the claim below is untrue.
The apeks 2nds are spring balanced...like "non-balanced" seconds.
I'm convinced they just have bigger user adjustable springs rather than the other
which use a small spring to hold the lever in-turn holding the seat against the cone that one cannot adjust. I dont think the air rebounds inside the chamber to counteract the spring...I think it goes in your mouth before it has time to rebound...
Can someone convince me otherwise and does this mean the poseidons are the only true pneumatically balanced seconds which is why they blast on startup???



PNEUMATICALLY BALANCED 2ND STAGE
All Apeks second stages feature a Pneumatically Balanced Valve System. In most second stage designs, the inhalation effort of the diver opens a valve inside the regulator that is held closed by spring tension. In the Apeks pneumatically balanced design, the pressure on the second stage valve is "balanced" by allowing medium pressure air to pass through to the opposite side of the valve to help counteract the force of the spring. This reduces the inhalation effort required to open the second stage valve and substantially improves the overall ease of breathing in all diving conditions.
 
All second stages are "balanced" in the sense that the downstream force of the air coming from the first stage must be balanced by pressure holding the seat against the orifice. The difference between a balanced second stage and a standard unbalanced second stage is that in the unbalanced second stage all of the force holding the seat against the orifice must come from the spring, while in the balanced second stage a significant amount of the force needed to press the seat against the orifice comes from the air pressure moving through the poppet and pushing on the back side of the poppet by means of the balance chamber.

One advantage of balancing is that you can then get by with a much lighter spring which tends to make for a more responsive poppet and induces less wear on the seat.

Another advantage is that the poppet is less sensitive to changes in IP. It must for safety reasons maintain a downstream bias, but a given change in intermediate pressure will have much less effect on inhalation effort.

A third advantage is that the size of the orifice can be increased to improve flow rate without having to increase spring pressure.

The bit in the Aqualung statement about the medium pressure air counteracting spring pressure is backwards - the pressure in the balance chamber augements spring pressure, it does not counteract it.

Poseiden second stages are different, but they are not the only balanced second stage around. They are however not downstream biased and must include some other mechanism for release of excess pressure.
 
I appreciate the thoughtful response and I was hoping to hear from you on this... but I would respectfully disagree.

"Balanced" suggests an apposing force (like the 2 chambers in the 1st that equalize eachother or balance eachother). The only opposing force in the TX 2nds are the springs.

I argue the downstream air bypassing the poppet is inconsequential in aiding or further placing compression on the spring and will not "augment" or lessen the spring's compression.

Based on these premise I'm not buying it....:shakehead:






DA Aquamaster:
All second stages are "balanced" in the sense that the downstream force of the air coming from the first stage must be balanced by pressure holding the seat against the orifice. The difference between a balanced second stage and a standard unbalanced second stage is that in the unbalanced second stage all of the force holding the seat against the orifice must come from the spring, while in the balanced second stage a significant amount of the force needed to press the seat against the orifice comes from the air pressure moving through the poppet and pushing on the back side of the poppet by means of the balance chamber.

One advantage of balancing is that you can then get by with a much lighter spring which tends to make for a more responsive poppet and induces less wear on the seat.

Another advantage is that the poppet is less sensitive to changes in IP. It must for safety reasons maintain a downstream bias, but a given change in intermediate pressure will have much less effect on inhalation effort.

A third advantage is that the size of the orifice can be increased to improve flow rate without having to increase spring pressure.

The bit in the Aqualung statement about the medium pressure air counteracting spring pressure is backwards - the pressure in the balance chamber augements spring pressure, it does not counteract it.

Poseiden second stages are different, but they are not the only balanced second stage around. They are however not downstream biased and must include some other mechanism for release of excess pressure.
Click to expand...
 
FFMDiver:
I appreciate the thoughtful response and I was hoping to hear from you on this... but I would respectfully disagree.

"Balanced" suggests an apposing force (like the 2 chambers in the 1st that equalize eachother or balance eachother). The only opposing force in the TX 2nds are the springs.

I argue the downstream air bypassing the poppet is inconsequential in aiding or further placing compression on the spring and will not "augment" or lessen the spring's compression.

Based on these premise I'm not buying it....:shakehead:
Click to expand...

Sorry you're not buying it, but this is exactly what balanced 2nd stages are, as explained by DA in the previous post. The balance chamber allows the downstream pressure of the air from the first stage to equalize on both sides of the poppet. That's your opposing force. Personally I don't know if the apeks 2nd stage you're talking about is in fact balanced, but given the great reputation of apeks regs, I would bet it is.
 
I find it somewhat non-intuitive that both sides equalize because the other end is open to your mouth. Your assertion sounds somewhat like the wandering bullet theory (see image below). Indeed a great reg. I use them. Although you may in fact be correct, I'm just looking for a more plausible explanation. But I'm glad your convinced of DAs explanation.



mattboy:
Sorry you're not buying it, but this is exactly what balanced 2nd stages are, as explained by DA in the previous post. The balance chamber allows the downstream pressure of the air from the first stage to equalize on both sides of the poppet. That's your opposing force. Personally I don't know if the apeks 2nd stage you're talking about is in fact balanced, but given the great reputation of apeks regs, I would bet it is.
Click to expand...
 

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There is a hole in the seat...only SOME air passes THRU the seat into the stem and rebounds back on the seat....TADA BALANCED...albeit only slightly... Duh...this SMALL amount of air never enters the main metal chamber, rather it remains in the plasic shuttle that holds the seat...ok I buy it!!! But given that I now understand it, I would not call it "balanced" at all....rather just a sensitivity assist because the two opposing forces are never really balanced in any true sense...only a small portion is "counter balanced" in my view. But you probably dont care about my view anyhow...:D
 
damn, you figured it out! I was about to set you straight... if the balancing chamber completely balanced the poppet, then there would be no need for the spring... besides would a "somewhat balanced" or an "almost balanced" reg really sell as well?
 
I would highly recommend that you get a copy of the "Regulator Savvy" book by Pete Wolfinger. It has good diagrams and good explanations.

Regulator Savvy

IMO, you are trying to think too much about air flow. Start by just thinking about the gas pressure times the area equal a force. The cross sectional area in the balancing chamber times the gas pressure provides a force acting in conjunction with the spring. The regulator is just balancing forces.
 
FFMDiver:
There is a hole in the seat...only SOME air passes THRU the seat into the stem and rebounds back on the seat....TADA BALANCED...albeit only slightly... Duh...this SMALL amount of air never enters the main metal chamber, rather it remains in the plasic shuttle that holds the seat...ok I buy it!!! But given that I now understand it, I would not call it "balanced" at all....rather just a sensitivity assist because the two opposing forces are never really balanced in any true sense...only a small portion is "counter balanced" in my view. But you probably dont care about my view anyhow...:D
Click to expand...

Call it what you would like. A normal, understandable term for that is a balanced barrel poppet 2nd.
 
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