Have regulators improved lately??

[Hoosier]

Really? how deep are you talking about? I was told that hard breath is affected from 500 psi.

 

[rescuediver009]

Boy you tech type guys can really "talk the talk" ....... is there a class to become a "dive/tech geek" or does it come natural ....... all I know is I love my MK10 and ever other year I take in in for cleaning and service and it has lasted me over 12 years without any problems ...... it breathes as good today as it did when I purchased it(2005 - 1988 ..... correction ..... make that 17 years) and I still wouldn't trade it for a MK25 or anything Apex ....

whether or not you have tried the regs that you say you refuse to upgrade to, it is that mentality that most people have when people ask them for a recommendation and as a result everyone recommends what they dive.

As for becoming a geek. I think that you have to walk to fine line between argueing about which reg draws how many tenths of an inch less water on the inhale (or worse the exhale) at 100ft. at 500psi..... thats where i refuse to go.

 

[turnerjd]

so much talk.........

Unbalanced vs balanced first stages.........

The difference is really quite simple. The first stage is designed to reduce tank pressure to ambient + 8.5 Bar (this is the figure for the Apeks that I have). They all do this. The difference between a balanced and unbalanced reg is that a balanced reg is far better at giving you ambient+8.5 at depth, and with tank pressure variations.

So, a balanced first stage at depth on a nearly empty tank should give ambient+8.5 bar, and the second stage should work almost as well as at the surface on a full tank.

An unbalanced first stage will not give you exactly ambient+8.5 at depth and at low tank pressure, the actual pressure will drop, and it will be significantly harder to breath from.

This measured pressure from the first stage is called the Intermediate pressure (IP). Usually at the surface this is 9.5 Bar (1Bar ambient + 8.5).
At 40m, this intermediate pressure would actually be 13.5 bar (5Bar ambient+8.5)....

The importance of this IP not changeing with depth is that the second stage always receives air at the same pressure, a pressure that is independent of the ambient pressure. The second stage mechanism being optimised (especially the spring) to receive air at the same pressure, works far less effectively as the IP drops.

Now, all well and good, but, if the balanced first stages are so much better, why are they still made? It's a question of cost vs necessity. for the majority of divers that never go below 20m (60ft) the drop in pressure is barely noticeable, and there is no nead for the extra complexity and cost associated with a balanced mechanism.

Hope that has cleared up the questions about balanced vs unbalanced

JonT

 

[DA Aquamaster]

I agree with most of what you say Jon, although at the end you confuse the issue and state that a lower IP will have a greater effect on inhalation resistance at depth. Depth has nothing to do with it. Whether you use an unbalanced reg at 10' or 150' you will notice the same increase in inhaltion resistance as tank pressure falls and it gets noticeable at pressures less than 500 psi.

Theoretically, since the air becomes denser and more viscous at depth, it will not flow as easily through the reg, but this is a very small effect and has no significant impact at depths encountered by open circuit divers.

The major performance limitation for most unbalanced regulator designs is that in order to keep the IP drop within a reasonable limit (approx 20 psi) to reduce the effect it has on inhalation resistance, the ratio of orifice area to piston head area must be kept within fairly narrow limits. So a larger orifice requires a larger piston head which in turns requires a larger regulator body and this escalation in size can quickly get out of hand. Consequently, unbalanced designs tend to have smaller orifices and less flow rate overall compared to balanced designs as on a balanced design the much downsteam force resulting from a larger orifice is balanced and the large change in downsteam force as tank pressure drops is negated and consequently has little or no effect on IP.

In terms of simplicity and reliability, an unbalanced piston design is impossible to beat and is consequently my first choice for a deco reg, so I think their appeal extends beyond shallow water divers.

 

[turnerjd]

I agree with most of what you say Jon, although at the end you confuse the issue and state that a lower IP will have a greater effect on inhalation resistance at depth. Depth has nothing to do with it. Whether you use an unbalanced reg at 10' or 150' you will notice the same increase in inhaltion resistance as tank pressure falls and it gets noticeable at pressures less than 500 psi.
<snip>
The major performance limitation for most unbalanced regulator designs is that in order to keep the IP drop within a reasonable limit (approx 20 psi) to reduce the effect it has on inhalation resistance, the ratio of orifice area to piston head area must be kept within fairly narrow limits. So a larger orifice requires a larger piston head which in turns requires a larger regulator body and this escalation in size can quickly get out of hand. Consequently, unbalanced designs tend to have smaller orifices and less flow rate overall compared to balanced designs as on a balanced design the much downsteam force resulting from a larger orifice is balanced and the large change in downsteam force as tank pressure drops is negated and consequently has little or no effect on IP.

<snip>

DA Aquamaster,

As far as I understand second stage design, if the IP drops once open the air will continue to flow for a shorter time since the second stage spring is designed to operate against a fixed pressure.

As I understand second stages (based on the Apeks), breathing in reduces the internal second stage pressure, moving the large membane. Moving this membrane moves the lever mechanism, opening the second stage valve. As air flows, the pressure in the second stage outlet (and by the membrane) rises, and eventually the second stage spring is able to close the air inlet valve. As I understand it, if the IP drops it becomes easier for the second stage inlet valve to close as the second stage spring is working against a lower pressure. So, to get a full breath it is necessary to continue breathing in, maintaining the internal second stage at an artificially low pressure so that the external membrane is pulled in slightly, and the inlet valve is held open artificially.

I do agree with the ration of piston/diaphragm to orifice and the resulting flow rate restrictions in unbalanced designs.

It has been some time since I have opened or played with a simple reg, but as far as I can remember the second stage is the reason for the increased WOB at lower flow rates/lower IP. I hope that I am not totally confused! (or confused anybody else).

I do also agree that unbalanced regs can make very good deco regs. They're cheep, very simple, robust, and at deco depths will work just fine.

JonT

 

[bahamasita]

What about double hose regulators? Heard they're making a comeback? What are the pros/cons? I was tempted to buy one b/c the bubbles won't come out right in your face, but is it worth it? I found the attached document comparing single hose and double hose regulators on one of the other threads, but it doesn't mean a whole lot to me. Anyone have first-hand experience or know something more about them?

 

[captain]

Although I frequently dive with my vintage double hose regulators I have not had the opportunity to try the new Aqua Lung Mistral. Two hose regulators do have different clearing procedures and breathing characteristics. If I were you I would try to find a shop that would let you try one before buying.

http://vintagescuba.proboards2.com/index.cgi?board=general&action=display&thread=1106087369

http://www.scubaboard.com/showthread.php?t=87742&highlight=mistral

 

[halocline]

The major performance limitation for most unbalanced regulator designs is that in order to keep the IP drop within a reasonable limit (approx 20 psi) to reduce the effect it has on inhalation resistance, the ratio of orifice area to piston head area must be kept within fairly narrow limits. So a larger orifice requires a larger piston head which in turns requires a larger regulator body and this escalation in size can quickly get out of hand. Consequently, unbalanced designs tend to have smaller orifices and less flow rate overall compared to balanced designs as on a balanced design the much downsteam force resulting from a larger orifice is balanced and the large change in downsteam force as tank pressure drops is negated and consequently has little or no effect on IP.

I assume the IP drop you're talking about is the gradual drop as tank pressure decreases, not the immediate drop that occurs with each inhalation, correct? So, when there is no inhalation, there is the combined force of the spring and ambient water pressure on one side of the piston head pushing it open, IP on the other side keepng it closed. Right so far? Okay, during inhalation, the IP drops, allowing the piston to open and air to flow. Very quickly, I assume, air rushes into the IP chamber and tries to close the piston, but continued drawing on that chamber keeps the IP just slightly below the amount needed to close the piston. So during an inhalation, the piston stays open? Is that right, or does the piston constantly open/close (maybe REALLY quickly) as IP varies during the inhalation. That seems unlikely.

Okay, now for the balanced/unbalanced part. If I understand, in unbalanced designs there is a constant downstream force on the piston orifice; this works with the spring and ambient pressure to try to open the piston. If this were a large amount of force, then you'd be introducing a larger variable in the opposing forces between opening and closing the piston. (Since that downstream force will drop as tank pressure drops) This is why the orifice must be smaller, unless the IP had a corresponding larger surface to exert more force on, i.e a larger piston head. In a balanced design, there is no downstream force on the piston.

There's a good diagram of a balanced piston 1st stage on the peterbuilt website, but I'm having trouble putting together in my mind the air path in an unbalanced piston. Where is the downstream force pushing on the piston? Is it inside the piston shaft pushing against the seat? I need a good diagram of the workings of an unbalanced piston 1st stage to get it figured out, I guess.

 

[DA Aquamaster]

There's a good diagram of a balanced piston 1st stage on the peterbuilt website, but I'm having trouble putting together in my mind the air path in an unbalanced piston. Where is the downstream force pushing on the piston? Is it inside the piston shaft pushing against the seat? I need a good diagram of the workings of an unbalanced piston 1st stage to get it figured out, I guess.

You have it all right so far. The piston is open anytime the pressure in the first stage is below the IP although how far it is open can vary a bit with the piston moving back and forth a bit.

In an balanced first stage the air enters the HP area of the first stage off to the side and does not press directly on the seat or on the end of the piston. The orifice is mounted on the end of the piston and the air flows through the piston to the IP section of the reg and to the second stage. The diamaeter of the piston stem where it is o-ring sealed to the regulator body stem is the same as the orifice diameter so there is no difference in the force exerted either way on the piston - ie it's balanced.

In contrast in the unbalanced piston first stage the orifice where air enters the first stage is on the regulator body and the seat is mounted on the end of the piston stem. So the air coming from the tank acts directly against the seat and assists in opening the piston and this force has to be countered by a higher IP acting on the piston head to close the piston. So as tank pressure falls, the amount of downstream force is reduced and IP is reduced accordingly.

The air flows through the orifice and then is diverted to the sides as it flows by the seat where it then feeds the LP ports directly. There are then 1 or 2 very small holes in the piston stem above the seat that supply another small hole drilled through the center of the piston stem to the piston head to supply the air pressure needed in the compression chamber to force the piston back down to close the seat on the orifice.

So balanced piston stages are often referred to as "flow through" stages while unbalanced piston stages are referred to as "flow by" stages due to the path of the air from the tank to the LP ports.

 

[DA Aquamaster]

DA Aquamaster,

As far as I understand second stage design, if the IP drops once open the air will continue to flow for a shorter time since the second stage spring is designed to operate against a fixed pressure.

As I understand second stages (based on the Apeks), breathing in reduces the internal second stage pressure, moving the large membane. Moving this membrane moves the lever mechanism, opening the second stage valve. As air flows, the pressure in the second stage outlet (and by the membrane) rises, and eventually the second stage spring is able to close the air inlet valve. As I understand it, if the IP drops it becomes easier for the second stage inlet valve to close as the second stage spring is working against a lower pressure. So, to get a full breath it is necessary to continue breathing in, maintaining the internal second stage at an artificially low pressure so that the external membrane is pulled in slightly, and the inlet valve is held open artificially...

IP drops about 10-20 psi on inhalation anyway regardless of tank pressure or whether the regulator is balanced or not. The IP drop however tends to be a little greater at full flow rates in unbalanced regulators since they generally are limited to a smaller orifice than in a balanced first stage design. But at less than a full flow rate (ie: during normal breathing) IP drop is pretty much same regardless of first stage design.

At the second stage, as soon as the poppet opens, the IP will fall and the poppet will lose much of the downstream assist acting on the seat. But air will also be exiting the second stage through the mouth piece. All second stages use aspirator bodies and ports to direct air out the mouthpiece and this flow of air out the mouthpiece creates a venturi effect that maintains a reduced pressure in the second stage case. This in turn keeps the diaphragm sucked in, keeps the lever depressed and keeps the poppet open until the diver stops inhaling, stops the flow of air and stops the venturi effect. On some regs the amount of the venturi effect is adjustable using an adjustable flow vane. But the net effect is that the venturi effect will allow the diaphragm and lever to make up for the lost downstream force with no increase in inhalation effort.

It has been some time since I have opened or played with a simple reg, but as far as I can remember the second stage is the reason for the increased WOB at lower flow rates/lower IP. I hope that I am not totally confused! (or confused anybody else).

Unbalanced downstream second stages have the same finite limit in orifice size as unbalanced first stages. A larger orifice means a larger spring force is needed to close the poppet against the downstream force. and it also means a greater difference in force as IP falls. So at low intermediate pressures (and less available downstream force), more force is needed from the lever and diaphragm. So to accommodate a larger orifice (with both higher flow rates and greater net change in downstream force as IP varies) you would need a larger diaphragm and/or a longer lever to maintain the same acceptably small increase in inhalation effort at low tank pressures. Consequently, an unbalanced downstream second stage will often have a smaller orifice than a balanced second stage and will consequently have less flow rate.

But ultimately, performance differences are not all that noticeable at the second stage until the conditions require high flow rates that begin to impact the IP significantly. However when the IP does fall significantly more than normal, the flow rate to the second stage decreases and the venturi effect in the second stage also decreases creating a situation where the diver has to literally suck air from the regulator to keep the poppet open. This is where the diver is over breathing the regulator and feels he/she is not gettign enough air from the regulator. Two divers inhaling hard simultaneously at 130 ft would probably put enough load on an unbalanced first stage to make a noticeable increase in inhaltion effort.