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

[Open Ocean Diver]

Just don’t see the difference between balanced and unbalanced between these two regulators, supply pressure 1100 psi.

Are balanced regulators all what the manufactures say they are cracked up to be. No pun intended. Lol

What I’m I missing?

Average flow (SP spec’s) is not that much different, IP between 115, 118 in both cases while flowing. I understand the principles with balanced regulators... lighter spring, easier to breath, immune to small IP changes. But my testing just doesn’t seem to prove that out.

I’m loving the 108 simplicity and no adjustment knob that I never use anyway.

Flow test: 108HP
Cracking .7
5 SCFM H20 1.0
8 SCFM H20 1.1
10 SCFM H20 1.1

SP catalogue:

Flow test: BA156
Cracking .8
5 SCFM H20 1.0
8 SCFM H20 1.0
10 SCFM H20 1.4

SP catalogue:

 

[tbone1004]

The cases are basically the same so the cracking pressures in a static environment when tuned the same, will respond the same. The 156ba by nature of the valve design will be smoother to breathe, though if it is enough to matter is something you have to decide. That does not mean that the cracking pressure will be any different.
The flow rates are determined by the valve diameter, and those are going to be similar which also explains your results.

What the 108 can't do is the IP compensation. That is very much noticeable on an unbalanced first stage across the range of supply pressures. Many first stages are also not perfectly compensating as a function of depth, particularly sealed diaphragms.

The adjustment knob allows you to tune a secondary second stage to much lighter cracking pressures and allow you to tune it back to minimize freeflow. The 108 doesn't allow you to do that.

Overall there isn't going to be much of a difference without an ANSTI machine

 

[Kupu]

I have owned and or rebuild quite a few 156 BA and and just a few 108 HP. Using a balanced first stage, I have found the 108 HP to be a smooth gem of a regulator right up there with my better performing 156s.

The standard 108s are fine, but the adjustable orifice of the 108 HP makes a tangible difference (in my experience).

 

[Open Ocean Diver]

I have owned and or rebuild quite a few 156 BA and and just a few 108 HP. Using a balanced first stage, I have found the 108 HP to be a smooth gem of a regulator right up there with my better performing 156s.

The standard 108s are fine, but the adjustable orifice of the 108 HP makes a tangible difference (in my experience).

With a balance first stage what’s your opinion on the 156 being a better performer than the 108?

 

[Kupu]

With a balance first stage what’s your opinion on the 156 being a better performer than the 108?

If 108 vs 156, then 156 wins easily.

But if 108HP vs 156 on subjective performance alone, and assuming both are top quality then calling it a draw might be the best I can come up with. I say that with some hesitation, being a long time user and big fan of the 156. I look forward to hearing other viewpoints and opinions, perhaps others have greater experience with the 108 HPs.

It is fairly well known that 156 performance quality can vary from one regulator to the next, sometimes reason for lesser performance can be discovered and remedied, and then sometimes it just seems to be baked in from the factory. Perhaps the simpler 108 HP design lends to more consistent performance for one regulator to the next, or maybe I have been lucky with the ones I pick up but they have all been great performers. I recently switched out a 156 in favor of 108 HP on my go to regulator set, partly just for something different and mostly because I like how easy it breathes.

 

[tbone1004]

@Kupu springs.... It's all in the springs. Especially with the older ones, the springs may not be up to spec any more. Something that is often overlooked at service.

 

[Kupu]

@Kupu springs.... It's all in the springs. Especially with the older ones, the springs may not be up to spec any more. Something that is often overlooked at service.

Valid point. When working thru a 156 or upgrading a 109, a new spring is one of the first things I try when performance is not up to par. Also checking for issues with orifice, balance chamber, lever including "upgrading" to curly foot lever (or the reverse) , looking for metal wear/roughness where the lever enters the barrel, cleaning the barrel, etc. All the points that have been discussed by the DIY crew that plays with these regulators.

On the 156, I can do all of the above and still have one that tunes easy on the first try with excellent performance, and another with just adequate performance even after hours of fiddling. Out of the ones I have rebuilt, around 30% end up awesome 60% perfectly fine and the rest just ok. Perhaps I can improve on that record with more experience. For me, G250s are more consistent in results after rebuild vs 156.

I wonder what the results would be if someone had 20 factory fresh 156/BAs tuned to perfection, each made in a different year. Would performance be equal on all of them, or would slight variations in tolerances reveal some to be naturally better than others?

 

[Open Ocean Diver]

Valid point. When working thru a 156 or upgrading a 109, a new spring is one of the first things I try when performance is not up to par. Also checking for issues with orifice, balance chamber, lever including "upgrading" to curly foot lever (or the reverse) , looking for metal wear/roughness where the lever enters the barrel, cleaning the barrel, etc. All the points that have been discussed by the DIY crew that plays with these regulators.

On the 156, I can do all of the above and still have one that tunes easy on the first try with excellent performance, and another with just adequate performance even after hours of fiddling. Out of the ones I have rebuilt, around 30% end up awesome 60% perfectly fine and the rest just ok. Perhaps I can improve on that record with more experience. For me, G250s are more consistent in results after rebuild vs 156.

I wonder what the results would be if someone had 20 factory fresh 156/BAs tuned to perfection, each made in a different year. Would performance be equal on all of them, or would slight variations in tolerances reveal some to be naturally better than others?

I have a NOS never wet 156 coming will be interesting to test it right out of the original box.

interesting I made a VIVA vane a while back for my BA, installed in the mouthpiece for fun the results were a drop from 1.4 to .9 H2o @10SCFM.

 

[Kupu]

I have a NOS never wet 156 coming will be interesting to test it right out of the original box.

1 down, 19 to go!

 

[Open Ocean Diver]

The cases are basically the same so the cracking pressures in a static environment when tuned the same, will respond the same. The 156ba by nature of the valve design will be smoother to breathe, though if it is enough to matter is something you have to decide. That does not mean that the cracking pressure will be any different.
The flow rates are determined by the valve diameter, and those are going to be similar which also explains your results.

What the 108 can't do is the IP compensation. That is very much noticeable on an unbalanced first stage across the range of supply pressures. Many first stages are also not perfectly compensating as a function of depth, particularly sealed diaphragms.

The adjustment knob allows you to tune a secondary second stage to much lighter cracking pressures and allow you to tune it back to minimize freeflow. The 108 doesn't allow you to do that.

Overall there isn't going to be much of a difference without an ANSTI machine

I have never tried the 108 with unbalance first stage. I’m testing with an MK5. I was surprised to see the dynamic flow effort at various flow rates to almost be equal and @ 10 SCFM the 108 actually out performs the 156.