breathing effort difference between 2 first stages...help

[JKSteger]

I am pretty sure the HOG is balanced as well. In any case I had a SP G200B on the bench so I ran though IPs ranging from 100 to 140 using a USD Conshelf for a first stage. I ran it several times and charted the results on my manometer as best as I could. While I was at it I also did an old Sherwood Magnum. Here are the results:

IP.............cracking pressure G-200B......Sherwood
140......................................0.625............1.25
130..................................... 0.75 ............ 1.50
120..................................... 0.875 ...........2.0
110 .....................................1.00 ............ 2.25
100..................................... 1.125............2.50

The Sherwood cracking pressure difference would be quite noticeable but the SP is less than 1 inWC across the 40 psi range I ran it through which is way out of the range I would expect even on an unbalanced first stage. It did not drop below 1.125 inWC even at 100 psi, still a passable cracking pressure.

Herman,
on Both the 1st stages they both crack at about the same. The difference is in the delivery of air. Using the Oceanic 1st, the air delivery is "good". It's not smooth and fluid, its really hard to describe in words but delivery is fine just not a natural smooth delivery.
On the Viper 1st, there is a very smooth, natural delivery. Almost like all i have to do is get the reg to crack and air is delivered to me without breathing it in but not being forced down my throat (I've had a few of them before)...strange I know!

The best way to describe it is this possibly. Take a G250 and turn the adjustment knob all the way to low, take a breath, that would represent the Oceanic. Then open the adjustment knob all the way open, take a breath, that would represent the Viper. Oh and the adjustment on the hog is open and the ventri is on the (+) side when I do this test on both regulator 1st stages.

Jeremy

 

[halocline]

Jeremy, if you take a G250 and turn the adjustment knob, you are increasing the cracking pressure, so if it's like that then the cracking pressure is what's changing. You can do an experiment; take the 2nd stage, connect it to one of the 1st stages, pressurize, and submerge it carefully (mouthpiece up) in a sink or bucket of water until it starts to flow. You'll get an idea of how deep you have to get the faceplate of the reg in the water until you hear the air. Then do the same with the other first stage. There will almost certainly be a big difference.

I think what you're experiencing in terms of flow is increased venturi effect with the 1st stage that has the higher IP. Higher IP equals more flow to the 2nd stage (if all other things are equal) which means the air is moving faster through the 2nd stage and increasing the venturi.

 

[LeadTurn_SD]

Herman: Thanks for going to the trouble to test the effects of various IP's on cracking pressure. I'd always been curious (but way too lazy to test!!) about the differences between balanced and unbalanced 2nd's in relation to changes in IP. It does look like your test "confirms" that balanced 2nd's will be much less sensitive to IP changes than unbalanced 2nd's.

What this reinforces for me is the need for a tech to really make an effort to properly/carefully tune an unbalanced 2nd stage to the first stage's IP, because it will be more likely to perform poorly (or freeflow) if the tech does a "quickie rebuild & test" and not a complete "test & fine-tune" on the regulator.

Best wishes.

 

[herman]

Glad to do it, always wondered myself, just never had the push to check it out. It does confirm my belief that the first stage is pretty much irrelevant and the second stage is all important in making a reg decision. I agree a balanced second stage makes the life of a lazy tech much better.

Jeremy, another possibility is a clogged filter on your Oceanic. If it's clogged it may have an acceptable IP with no flow...which would give you the same cracking pressure but then do some strange things once the flow increased and IP dropped. Get yourself an IP gauge, it's the best $20 accessory a diver can have.

 

[JKSteger]

I think what you're experiencing in terms of flow is increased venturi effect with the 1st stage that has the higher IP. Higher IP equals more flow to the 2nd stage (if all other things are equal) which means the air is moving faster through the 2nd stage and increasing the venturi.

You know Mattboy, I think you are right about what I am experiencing. I think my Oceanic just needs a good adjusting!

Jeremy

 

[Couv]

Herman, your experiment was awesome….thank you.

To the OP, If I read your post correctly, you are moving the second stage, including the hose, from one first stage to another and getting noticeable differences in performance. As Herman et al pointed out, the IP is probably not the issue. That leaves either the first stage, or the tank and valve. The easiest to eliminate would be the tank/valve by using the same one for each of your test. If you are already using the same tank/valve then it time to examine the first stage. There may be a restriction somewhere. I would start with the filter. Any corrosion or contaminates in there? Does this regulator have one of those funky check valves at the air inlet? If so, it may be faulty.

Have a good look and keep us posted.

Couv

 

[halocline]

If we're going to start a friendly wager, my bet is on IP and the HOG is unbalanced.

 

[JKSteger]

I'm reading on other forums that the HOG second is a Balanced 2nd stage. Phill Ellis, Joel from Tech Diving Limited and others are stating that the 2nd stage is in fact an pneumatic balanced 2nd with venturi and breathing adjustment knob!

I tried the same setup with my old Mares Mr12 and it breathed as good as the Viper too!

Jeremy

 

[Bubbletrubble]

If we're going to start a friendly wager, my bet is on IP and the HOG is unbalanced.

I bet you're only half right. I think the HOG 2nd stage is balanced. Geesh, I wish I had bought one of them during the Black Friday sale ($50 each)...just so I could take it apart and compare it to my Apeks second stages.

 

[Fishpie]

The Hog 2nd stage is balanced.....I posted a 1st impressions review here:
http://www.scubaboard.com/forums/regulators/314289-hog-2nd-stage-arrived.html