Balanced or unbalanced?

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JDMerk

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I bought a set of used regulators:
Sherwood Magnum first and second and oceanic delta 3 octo

Problem is that I have been told by two different LDS that it is balanced and that it is unbalanced. Is there an easy way to tell? Were there even any unbalanced Magnums?

Also was the delta always a balanced regulator? I am actually using the delta as my primary because it breathes so much easier.

The reason I ask is because I am diving key largo in a couple weeks and will hit 130' in my AOW class...i kinda want to know what to expect.
 
Balanced piston design ...
Welcome to Sherwood Scuba!

"balanced" is a first stage feature. The term doesn't apply
to second stages. Did you mean was the Delta's original 1st a balanced reg? Not sure. Does that make sense?

Sorry to disagree but balanced can be a feature of either (or both) stages of a reg. Most all high preformance seconds are balanced as are many first stages.

Looking over my Sherwood service manuals as best as I can tell, all of the Sherwood Mag first stages are balanced and all of the seconds I saw are non-balanced. According to a 2003 scubadiving mag test, the Delta 3 second is balanced, never had one in my hands however. Scuba Diving Magazine - Best New Regs 2003

As for which breaths easier, that can be a function of a lot of things, both with the design of the reg and the skill (or give-a-shxx factor) of the last tech to tune them.
 
If memory serves, the Sherwood Magnum first stage was balanced, and both second stages were unbalanced.
 
Balanced does apply to both stages. A "balanced" stage is one in which the downstream force of the air entering it is "balanced" by a small amount of air that has been diverted and is supplying a countering upstream force. The idea is to negate the effect of changing supply pressure on the stage.

First stages see a very large range of supply pressure (3000 to 500PSI or so), and so balancing has the effect of helping the first stage put out a constant IP to the 2nd stage regardless of how much air is in the tank. Second stages are not subjected to a wide range of supply pressure, they only see IP, and so balancing in the 2nd stage is, in general, not considered as important. But, since 2nd stage valves are much more sensitive and are directly responsible for the breathing effort, balancing can allow the use of a lighter spring and theoretically lower WOB. That's only with all other things equal; in reality there are lots of other factors in determining how a reg breathes.

Most sherwood 1st stages are not exactly air balanced; they use an unbalanced piston design and mount the HP seat on spring washers which stabilize the IP throughout the supply range. Assuming your magnum is one of these, the truth is it's "sort of" balanced in the sense that there is not the typical air balancing chamber, but the spring washers do more or less the same thing. If you want to a little geeky about it, borrow an IP gauge, put it on your Lp inflator hose, and check the Ip with a full tank and then with a near empty (500PSI) tank. If the IP is close to the same in both cases, you have a functionally balanced 1 stage. If its 15PSI or so lower with the low tank, it's unbalanced.

Truthfully it won't make much difference in your diving. I'm pretty familiar with the effects of an unbalanced piston 1st stage because I own a SP MK2 and have used it extensively with an unbalanced R190 2nd stage. My experience is that the reg begins to breathe a little (Really a LITTLE) more stiffly at 500 PSI, and becomes pretty evident at 300 PSI. It's pretty unlikely that you're going to be at any sort of depth with that low a tank pressure unless something is wrong. If that's the case (like a broken SPG) the reminder is not a bad thing at all.

Balancing has no effect on how the reg performs at depth, all other things equal. All regs compensate for depth in the same way, balanced or unbalanced. One reason that some people mistakenly think there's a relationship between depth performance and balancing is that balanced stages are most associated with higher flow, higher end regs that perform better at depth anyways.

I've had my MK2 down to 130 ft and it works just fine. I believe it's capable of supply around 70SCFM at low tank pressure, which is still more air than any 2nd stage can flow. So, don't worry about your reg at all; I"m sure it will be fine.
 
Most sherwood 1st stages are not exactly air balanced; they use an unbalanced piston design and mount the HP seat on spring washers which stabilize the IP throughout the supply range. Assuming your magnum is one of these, the truth is it's "sort of" balanced in the sense that there is not the typical air balancing chamber, but the spring washers do more or less the same thing.

Balancing has no effect on how the reg performs at depth, all other things equal. All regs compensate for depth in the same way, balanced or unbalanced. One reason that some people mistakenly think there's a relationship between depth performance and balancing is that balanced stages are most associated with higher flow, higher end regs that perform better at depth anyways.

I've had my MK2 down to 130 ft and it works just fine. I believe it's capable of supply around 70SCFM at low tank pressure, which is still more air than any 2nd stage can flow. So, don't worry about your reg at all; I"m sure it will be fine.

Quoting this because I would have said most of this. (Didn't this just come up about the Maximus?)

Sherwood's first stages are not 'balanced' (where balanced means that the piston moves perpendicular to the air pressure from the tank, which is how ScubaPro defines it in their regulator terminology). On the other hand, any first stage is 'balanced' in that in can shut off the full tank pressure by couteracting the force hydaulically, (which is what 'balanced' means in another sense). But the terms 'balanced' and 'over-balanced' are thrown around a lot in marketing speak.

The old Brut first stage did not even use those washers, right? (I cannot remember.)

In my experience, I can outpace a MK2, but only at rec limits (120-130ft). I love unbalanced piston designs, but I can make the tiny little hole that all Sherwoods (and all other unbalanced piston designs) deliver air through not supply enough to supply a second stage and a power inflator, for instance. Personally I don't like the dry air bleed system that old school Sherwoods used because when they crap out, they crap out hard, and you just cannot rebuild them. But then again open spring designs like the MK2 can crap out from corrosion and silt in the spring chamber.
 
As has been mentioned, since the first stage intermediate pressure of modern regulators is constant, there is no variance which might require compensation or "balancing" at the second stage. Hence, second stages are not balanced, no exceptions that I am aware of. Many years ago, Scubapro decided to use dual springs in their second stages; one of the springs is mechanical and the other is pneumatic. Unlike a mechanical spring, the pneumatic spring exerts force on the second stage poppet only when the system is pressurized. Concerning the design, Scubapro, instead of using a separate tube to supply air to the pneumatic spring, arrived at the clever and economical idea of supplying the air through a hole drilled in the poppet itself. The appearance of this thing gives one the impression that it is similar to the US Divers balanced valve design used in the Royal Aqua-Master and Conshelf first stages. However, it is not like that at all. When the Scubapro second stage is delivering air to the user, the supply of air to the pneumatic spring is cut off leaving only the mechanical spring to control flow. Supposedly, this would reduce breathing effort after the valve has cracked but since Venturi devices in most regulators already accomplish this the point of the "balanced" second stage is not clear. It does have one advantage that has been claimed and I feel it has some validity; during a resting state (air off) there is somewhat less force on the soft poppet seat. This is probably beneficial inasmuch as the seat will undergo less long term wear ("engraving").
 
As has been mentioned, since the first stage intermediate pressure of modern regulators is constant, there is no variance which might require compensation or "balancing" at the second stage. Hence, second stages are not balanced, no exceptions that I am aware of.

With all due respect, I think it's silly to think of the D series as "not balanced". The air enters the aspirator chamber and exerts a downstream pressure on the seat as well as upstream pressure on the other end of the spool. You can't get a clearer example of air balancing as it applies to scuba regulators.

I also believe you're somewhat splitting hairs with the idea of "dual springs, one mechanical, one pneumatic" in the barrel poppet balanced stages like the B/A and G250. Again, air is diverted (through the poppet as you explain) so that a portion of the downstream air force is counteracted by an upstream force. This is precisely how regulator engineers have described air balancing. I understand that when the 2nd stage valve opens, there is also a drop in pressure in the balance chamber, lowering the upstream balancing effect. However, that drop is caused by the drop in downstream IP that occurs with each opening of the valve, so the forces remain in "balance."
 
I'm familiar with the engineers (and sales) description of "air balancing". Similar goals are accomplished with a single mechanical spring with the exception of "let off" after pressure is removed. In both designs, air pressure is opposed by an arrangement of springs; it is as simple as that. Except for price, it is not particularly important that one design uses two springs and the other, a single spring. All regulators are balanced in the sense that all parts are in stasis (static balance) until air flows. After that, the parts are in temporary dynamic balance. However, aside from the engineering, there is the diver's lexicon. US Divers originally used the term "balance" to describe a proprietary design in their revolutionary first stage. To have this coopted and twisted in the name of engineering is somewhat insulting and unsettling. It is a misrepresentation (or ignorance) on the part of Scubapro to gain commercial advantage. This kind of manipulation of language interferes with the ability of new divers and some not so new as to understand the function and value of competing regulator designs. As far as "balance" applied to various first stage designs, whether these designs involve floating orifice's or "flow through" pistons, I have no problem with that. These alternative designs actually do function as balance valves as understood by divers (including engineers), eg, to stabilize interstage pressures.

For those who care about these things, the Scubapro second stage is spring operated with a dual system, mechanical and pneumatic. The pneumatic helper spring is a classic piston and barrel. The amount of spring force exerted by the pneumatic spring is determined by air pressure and size of the piston. In other words, the design translates air pressure to a specific spring force through selection of the size of the piston and barrel. Theoretically, any amount of force could be applied by reducing or enlarging the piston. Thus, the force is applied by a mechanical device, not air pressure per se which means that "air balancing" was not even a consideration beyond that which applies to any regulator design, eg, to install just the right amount of balance between air pressure and opposing spring force. The real goal was poppet "let off" without disrupting the primary function, breathing. Scubapro engineers were looking for a compromise which would not throw the regulator into a tizzy but still have some effect. Thus, the force applied by the piston is a compromise between flow and stability. If the piston were too large, the whole thing would go into free flow as soon as the poppet was upset. If too small, the pneumatic spring would not be functional and all the load would be carried by the mechanical spring alone. So, one can see that the design is not a simple matter of air pressure pushing against one side of the poppet and equal, opposing pressure on the other side. The "balance chamber" is actually a piston ram which applies a predetermined force to assist the primary spring.

This design was a huge commercial success mostly due to the mystique of "balancing". However, efforts to unload the poppet continued with various results but all added some complication. If my opinion were sought on this matter, I would give the nod to Sherwood's SR-1 floating orifice which is simple and effective.

One can't just go around calling things whatever they like. Of course, they do and they get away with it. The usual motive is political advantage or commercial gain. In this small instance, the question of what to call a regulator part, a company glamorized a mundane pneumatic spring by asserting that it was something else and had special properties which were all out of proportion to fact. It is an easy game to play if one has an advertising budget and duplicitous or ignorant people posing as instructors representing some organization with an impressive name. So, if Scubapro were to order them to say that a balloon was actually a "balanced sphere" and a teeter totter was to be referred to as a "balanced beam" they would try hard to sell the toys with a fancy name and price to match. What is scary is that they might succeed.
 
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