just a basic question on the difference between an pneumatically and mechanically balanced 2nd stage. I mean I understand the physical difference but how does this translate into performance and different usability? also, I have the Ocean GT3 ordered, decent reg?
pneumatically vs mechanically balanced
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redacted
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Mechanically balanced seems to be a term used to describe an adjustable 2nd that usually has a fairly sensitive fine adjustment capability. With a sound design, they can perform quite well (look at a Kirby Morgan) but may require more active management by the user to achieve best performance. Pneumatically balanced is a more common design, usually simpler (lower parts count) and provides a partial compensation for any changes in IP as a function of tank pressure and allow the use of a lighter mechanical spring. The benefits of pneumatic balancing are provided without any user action (other than breathing).
The term mechanically balanced is also commonly used for any down stream demand valve when is carefully adjusted. In this situation the IP (pneumatic) force is close to being balanced with the force of the mechanical spring.
The adjustment can be accomplished by either adjusting the mechanical spring force or the intermediate pressure (IP) so that the forces balance each other. This is in theory possible with most down stream demand valves, but in practice some regulators become unstable and tend to leak.
The adjustment can be accomplished by either adjusting the mechanical spring force or the intermediate pressure (IP) so that the forces balance each other. This is in theory possible with most down stream demand valves, but in practice some regulators become unstable and tend to leak.
Mechanically balanced 2nd stages like the Oceanic deltas use 2 springs in their designs. A primary spring at the poppet and a secondary spring at the adjustment knob to achieve a balance. For example if you use it with an unbalanced 1st stage that drops IP from 145psi to 125psi and in order to maintain an optimal performance you should adjust your knob (secondary spring tension) from 25psi to 5psi accordingly (I just made up some numbers here).
IP from tank should be balanced with Primary spring tension + secondary spring tension.
For example:
Full tank at 145 psi = 120 psi + 25 psi (knob adjustment)
Low tank at 125 psi = 120 psi + 5 psi (knob adjustment)
If they are balanced, all you need is very minimal effort to crack open the valve.
In pneumatically balanced 2nd stages, like Scubapro for example, the secondary springs are being replaced by air chambers instead of physical springs. They function the same and I believe the control knobs are also used for fine adjustments. Because of the secondary spring effect, both mechanical and pneumatic 2nd stages can use lighter main springs.
IP from tank should be balanced with Primary spring tension + secondary spring tension.
For example:
Full tank at 145 psi = 120 psi + 25 psi (knob adjustment)
Low tank at 125 psi = 120 psi + 5 psi (knob adjustment)
If they are balanced, all you need is very minimal effort to crack open the valve.
In pneumatically balanced 2nd stages, like Scubapro for example, the secondary springs are being replaced by air chambers instead of physical springs. They function the same and I believe the control knobs are also used for fine adjustments. Because of the secondary spring effect, both mechanical and pneumatic 2nd stages can use lighter main springs.
halocline
Contributor
I still don't understand the use of the term "mechanically balanced" in this context, it sounds like you're just talking about adjustable 2nd stages, regardless of one spring or two. Of course, it's common for the dive gear industry to toss around 'technical' terms, inaccurately, in hopes of selling a few more regulators. "Overbalanced" regs are an example of this.
Balanced valves are supposed to automatically adjust so that changes in supply pressure have no (or little) effect on the functioning of the valve. Typically this is done by routing supply air so that it exerts force on both sides of the valve, essentially canceling itself out in terms of influence on that valve. That's "pneumatic" balancing. The only "mechanically balanced" scuba valve that comes to my mind is the Sherwood style 1st stage floating orifice, where changes in supply pressure change the position of the orifice, which in turn compensates for changing downstream pressure on the HP seat. I suppose the closest thing to that in 2nd stages (that I can think of, I'm sure there are other examples) would be the floating orifice seat-saver like on atomic 2nd stages. But that's not really mechanical balancing, it's just a tricky way of keeping the orifice off the seat until the reg is pressurized.
Balanced valves are supposed to automatically adjust so that changes in supply pressure have no (or little) effect on the functioning of the valve. Typically this is done by routing supply air so that it exerts force on both sides of the valve, essentially canceling itself out in terms of influence on that valve. That's "pneumatic" balancing. The only "mechanically balanced" scuba valve that comes to my mind is the Sherwood style 1st stage floating orifice, where changes in supply pressure change the position of the orifice, which in turn compensates for changing downstream pressure on the HP seat. I suppose the closest thing to that in 2nd stages (that I can think of, I'm sure there are other examples) would be the floating orifice seat-saver like on atomic 2nd stages. But that's not really mechanical balancing, it's just a tricky way of keeping the orifice off the seat until the reg is pressurized.
Zung
Contributor
+1
I fully agree with halocline.
Strictly speaking, balanced means:
Force (IP) = Counter Force (spring)
But in the case of a second stage, it doesn't mean much because it's the only way to stop the flow. Adding an extra spring doesn't achieve anything.
OTOH, a smarter design could be:
Force (IP) = Weaker Counter-Force (weaker spring) + part of the IP reversed in direction
That's a lot more interesting because the system adjusts itself to the incoming IP, at least to some extend.
I fully agree with halocline.
Strictly speaking, balanced means:
Force (IP) = Counter Force (spring)
But in the case of a second stage, it doesn't mean much because it's the only way to stop the flow. Adding an extra spring doesn't achieve anything.
OTOH, a smarter design could be:
Force (IP) = Weaker Counter-Force (weaker spring) + part of the IP reversed in direction
That's a lot more interesting because the system adjusts itself to the incoming IP, at least to some extend.
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