Max depth for unbalanced regs???

[SeaHound]

Yes and no, the Royal Aqua Master is fully balanced and is the same first stage as used in the Conshelf/Titan.

I understand what and how, I was wondering which one the OP is concerned about specifically.

N

150 dollar range "economy regs" like Mares Rebel etc. It used to be the stuff only dive shops would get and that also for shallow dives. Aqualung Calypso would be another one I guess.

 

[Splitlip]

I think the "Rebel" is a second stage.

I think it is usually paired with MR12 1st stage which is balanced I believe.

 

[Nemrod]

Unbalanced regulators:

Diaphragm 1st stage-IP increases as tank pressure drops. (none made anymore that I know of)

Piston1st stage-IP decreases as tank pressure drops.

c

Thanks for that correction, that is an excellent point. So much we think of diaphram units and forget that a piston regulators is an excellent unit.

N

 

[halocline]

An unbalanced reg becomes harder to breath as depth increases or tank pressure decreases. It is more a function of the tank pressure as I don't think we could could dive traditionaly deep enough to render the reg unbreathable.

A blanced reg delivers the same ip regardless of depth or tank pressure.Then they shut off

I used unbalanced regs alot in the 70's and 80's. They started pulling hard and we knew it was time to surface. As we surfaced we were able to breath.

Depth compensation has nothing to do with balanced or unbalanced regs; all regs increase the IP as depth increases. This is done exactly the same way in balanced and unbalanced regs, by introducing ambient pressure as a force working against IP in the 1st stage. Otherwise, the reg would not work at any sort of depth.

Balanced 1st stages have greater stability of IP throughout the entire tank range than unbalanced regs...although I have noticed that my balanced MK5 drops a good 7-10 PSI from 3000-500PSI supply pressure and my (unbalanced) MK2 drops about 12-15, so in practicality there's not a huge difference between those two. My guess is that many balanced diaphragm regs in practice do have a slight IP rise throughout the supply pressure range, not that it matters much. In any event, it has nothing to with depth.

One design factor in unbalanced piston regs (the only kind of unbalanced regs on the market) is that the orifice surface area must be kept small to minimize the actual drop in IP by making downstream pressure on the seat a smaller percentage of the total force at work. This limits the practical flow rate, so theoretically if you and a few of your friends were huffing away off the same MK2 at 150 ft, you "might" overbreathe it. The MK2 has a flow rate of almost 100 SCFM, which means it flows faster than the tank valve. If I were a trained tech diver and could do a 200 ft dive, I'd have no problem taking my MK2 that deep.

Balanced 2nd stages use a lighter spring to keep the valve closed and are less reactive to IP changes, so typically a well designed balanced 2nd stage will have lower cracking effort and WOB than an unbalanced. But, in otherwise identical designs, balanced vs unbalanced will result in very little difference.

The terms "balanced" vs "unbalanced" are pretty loaded from a marketing point of view. Who wouldn't prefer "balanced" to "unbalanced" even without knowing what the difference is? Even the PADI OW and AOW books make a stupid reference to it which explains nothing but sends the clear message that "balanced" is better.

 

[redacted]

Balanced 2nd stages use a lighter spring to keep the valve closed and are less reactive to IP changes, so typically a well designed balanced 2nd stage will have lower cracking effort and WOB than an unbalanced. But, in otherwise identical designs, balanced vs unbalanced will result in very little difference.

I believe cracking effort will stay the same and is largely a matter of design quality and how close you can set it and still maintain reliable operations. To "crack" the seal, you have to drop the pressure in the second enough to overcome the total "spring" force that is holding the poppet seated regardless of whether that force comes from a mechanical or a pneumatic "spring". You should expect overall WOB to drop with the balanced 2nd since the residual force you have to contend with on the inhale cycle is the lighter mechanical spring. But because of case geometry and venturi effects it is not as simple as half the mechanical spring force and half the inhale portion of the WOB. I usually find it difficult to sense the difference between my Adjustables and my Balanced Adjustables.

 

[Trimix2dive]

sorry never taken old school below rec limits. draw did get a bit heavy, if memory serves.

 

[halocline]

I believe cracking effort will stay the same and is largely a matter of design quality and how close you can set it and still maintain reliable operations. To "crack" the seal, you have to drop the pressure in the second enough to overcome the total "spring" force that is holding the poppet seated regardless of whether that force comes from a mechanical or a pneumatic "spring". You should expect overall WOB to drop with the balanced 2nd since the residual force you have to contend with on the inhale cycle is the lighter mechanical spring. But because of case geometry and venturi effects it is not as simple as half the mechanical spring force and half the inhale portion of the WOB. I usually find it difficult to sense the difference between my Adjustables and my Balanced Adjustables.

I see what you mean, initial cracking should be the same, but keeping it open should be theoretically easier with a balanced stage. The pressure in the balance chamber will not drop until the reg opens. Good call.

 

[mikeguerrero]

But what about all this talk about overbalance 1st stage vs balanced 1st stage? Is this a bunch of bull? Something about diving deeper with a over balance will breathe better than just balance. Then I hear that even if you have an over balanced 1st stage the 2nd stage being neumatically balanced will kill the funtion of the over balance anyway...

Anyone have any insight?

Thanks,

 

[Luis H]

It is good to see that some of “the usual suspects” showed up with some good explanations. For a moment this thread looked like a runaway train.

The explanation from Mattboy is very good (with the minor correction from Awap).

The only thing I would like to add is that personally, when speaking about second stages, I like to use the term “pneumatically balanced” second stages.

In a properly adjusted conventional (down stream demand valve) second stage all the forces should be very closed to balanced. The spring force is basically balancing the pneumatic force caused by the intermediate pressure pushing on the soft seat. This is often referred to as mechanically balanced.

 

[Luis H]

How about a Poseidon Cyclon 300?

I am fairly certain the Poseidon Cyklon 300 was the last unbalanced diaphragm first stage in production. They were around into the late 70’s, but I am not sure when they were replaced by the Cyklon 5000.

Unbalanced regulators:

Diaphragm 1st stage-IP increases as tank pressure drops. (none made anymore that I know of)

Piston1st stage-IP decreases as tank pressure drops.

c

Thanks for posting the difference. Since unbalanced diaphragms first stages have not being manufactured for a few decades they are often forgotten, but there are plenty of Cyklon 300 and Aqua Masters out there in use.