What’s the deal... SP 108 HP verses 156BA

[Open Ocean Diver]

I think it just clicked in thank you that’s a great explanation something that should be added to the book. So to summarize when the valve first cracks IP drops upstream force is less and the valve becomes easier to open with the lighter spring? Lightbulb moment.

Wait a minute that can’t be right, with my test set up I notice after cracking as the IP dips the effort on the mag gauge increases then when the IP recovers it goes back down to something close to where initially cracked open. Hmmm confused

 

[tbone1004]

What a minute that can’t be right, with my test set up I notice after cracking as the IP dips the effort on the mag gauge increases then when the IP recovers it goes back down to something close to where initially cracked open. Hmmm confused

with an unbalanced-downstream valve design, the spring pressure is fighting the IP. As you inhale, the lever is assisting the IP to work against the spring. The pressure required to move the lever is the cracking pressure. As you inhale, the IP drops and the lever has to work harder to keep the valve open.
With a balanced-downstream valve design, the spring pressure is much lighter since the spring is assisted by the IP itself. When the IP drops, it drops on both sides of the seat, so the change in cracking pressure is much smaller as the IP drops.
The higher the performance of the first stage, the less the IP will drop while you are breathing. The lower performance, the worse it gets. About the worst setup you can have is an unbalanced second stage on a low performing unbalanced first stage. Aka something like a 108 on a Mk2. Put that 108 on a MK25 and you may not notice much of a difference between a 108 and a 156. Point is you have to look at the entire system of the first and second stage *which is why CE ratings are given as a regulator system and not on any individual regulator stages*, but you also need to look at the area under the curve during a breathing cycle instead of just the cracking pressure.

 

[Open Ocean Diver]

with an unbalanced-downstream valve design, the spring pressure is fighting the IP. As you inhale, the lever is assisting the IP to work against the spring. The pressure required to move the lever is the cracking pressure. As you inhale, the IP drops and the lever has to work harder to keep the valve open.

I have a machine I built that draws on the regulator in a consistent way, variable from 0 to 5 LPM. Once the valve cracks, I measured the effort when IP dips, I keep the valve open and I can see the effort increase as the IP continue to drops and then when IP recovers, the effort settles back to where it initially cracked open. I can see what you are saying above testing this way very consistently.

With a balanced-downstream valve design, the spring pressure is much lighter since the spring is assisted by the IP itself. When the IP drops, it drops on both sides of the seat, so the change in cracking pressure is much smaller as the IP drops.

However with the balanced 156 testing the same way I see the same results. I am testIng both with the same balanced MK5.

I understand most balance seconds come with a balanced first stage, I was just trying to measure the benefits of a balance second compared to an unbalanced 108 connected to a balanced fist stage and from what you and others are saying with a balanced first stage probably won’t notice much difference so I guess I’m see that.

Thanks,

 

[halocline]

Once air is flowing through the regulator, venturi effect comes into play and that has a big influence on WOB numbers. We haven’t talked about that yet, it’s a whole different topic. Also, I’m not sure how you are measuring these numbers. For example an IP gauge will not usually accurately measure IP while air is flowing through the hoses because it is also subject to venturi effect.

 

[Open Ocean Diver]

Once air is flowing through the regulator, venturi effect comes into play and that has a big influence on WOB numbers. We haven’t talked about that yet, it’s a whole different topic. Also, I’m not sure how you are measuring these numbers. For example an IP gauge will not usually accurately measure IP while air is flowing through the hoses because it is also subject to venturi effect.

In the above case I’m only flowing 0-5lpm, and don’t really need to rely on the IP gauge, I can see the opening of the valve with the mag gauge alone. The Percision is amazing. I can detect things like the smoothness of the lever action that I never could before by just sipping on the mouthpiece. My experience is it’s only when I flow something like over 5 SCFM and above with the regulators I have that I really see the Venturi effect kicking in. When does the Venturi effect actually come into place? You’re throwing a wrench into my thinking. Lol

 

[tbone1004]

In the above case I’m only flowing 0-5lpm, and don’t really need to rely on the IP gauge, I can see the opening of the valve with the mag gauge alone. The Percision is amazing. I can detect things like the smoothness of the lever action that I never could before by just sipping on the mouthpiece. My experience is it’s only when I flow something like over 5 SCFM and above with the regulators I have that I really see the Venturi effect kicking in. When does the Venturi effect actually come into place? You’re throwing a wrench into my thinking. Lol

0-5lpm over what time period? While we do typically only breathe around 0.5cfm at the surface, we are also only inhaling about 25% of the time so the inhale phase is about 4x the average flow rate.
Venturi kicks in far sooner than that though. If you see the magnehelic drop at all, that's the venturi kicking in. It may not be by much, but if it has any sort of drop after the initial cracking effort, that is the venturi effect. How much it drops is determined by the case and valve geometry, but it is there. There is not a whole lot of venturi on the older regulators though and that was the big upgrades when they became the G series.

 

[Open Ocean Diver]

0-5lpm over what time period? While we do typically only breathe around 0.5cfm at the surface, we are also only inhaling about 25% of the time so the inhale phase is about 4x the average flow rate.
Venturi kicks in far sooner than that though. If you see the magnehelic drop at all, that's the venturi kicking in. It may not be by much, but if it has any sort of drop after the initial cracking effort, that is the venturi effect. How much it drops is determined by the case and valve geometry, but it is there. There is not a whole lot of venturi on the older regulators though and that was the big upgrades when they became the G series.

The pump just takes over manually sipping/sucking on your regulator with incredible consistency to measure cracking effort. If I could be extremely consistent with my sipping on my regulator once the IP drops and I measure the cracking effort, as the IP continues to drop a bit more you can see the effort increases as the IP recovers you can see the effort going back to its original place were it just cracked. It’s very cool.

As you turn up the microVav the mag gauge climbs and when the valve Just opens the gauge drops indicating cracking effort even before you can detect IP dip.

I have a much larger system to really flow the regulator to see the Venturi effect. One time I experimented and put a VIVA vane in my 109 and measured the Venturi effect really made a difference.

 

[halocline]

When does the Venturi effect actually come into place? You’re throwing a wrench into my thinking. Lol

Whenever air is flowing in a directional manner it will create lower pressure in the area surrounding it. That's basic physics, I guess. Now, how much and how fast is a question for someone smarter than me. In scuba regulator use, it has a big effect on inhalation effort after the valve is cracked open and air starts to flow. That's as specific as I could get, sorry it doesn't really answer your question.

But I have to ask, are these tests on your part just out of curiosity, or do you have some specific goal in mind other than increased knowledge?

 

[Open Ocean Diver]

Whenever air is flowing in a directional manner it will create lower pressure in the area surrounding it. That's basic physics, I guess. Now, how much and how fast is a question for someone smarter than me. In scuba regulator use, it has a big effect on inhalation effort after the valve is cracked open and air starts to flow. That's as specific as I could get, sorry it doesn't really answer your question.

But I have to ask, are these tests on your part just out of curiosity, or do you have some specific goal in mind other than increased knowledge?[/QUOTE

Thank you

just started repairing my own regulators and now its become somewhat of an addiction. Lol