Conservative Tech?

[Ojai Diver]

When my prior regulator set got serviced, the tech returned it to "factory specs."

It did not breath that great. It took repeated trips to the tech, several adjustments (increasing the IP pressure) to get it right-- or at least, much better.

Recently, I got a new reg set (I am deliberately not giving reg brands here), the tech connected the second to the first, "tuned it" and same thing, it breathed poorly, and it took several trips back to him to adjust (again, in part by raising IP) to get it breathing better.

Is there some sort of reluctance for techs generally to set the IP pressure higher? This tech appears to be very competent.

 

[fmerkel]

So, what is the 'spec' and what IP did you end up using?

I don't find any appreciable difference if the IP on about any of my regs (diaphragm and piston, major brands) is a little below spec, or above spec, as long as the 2nd stage is tuned to it.

 

[rsingler]

It is the second stage cracking effort that is the key to ease of breathing, in most cases. Raising the IP of the first stage with a balanced second stage will likely do nothing.
But yes, many shops will adjust second stages to the top of the specification, and they will breathe quite stiffly. Most divers don't know the difference.
The shop reasoning is that as the seat of the 2nd takes a "set", it gets indented. That indentation has the same effect as decreasing the cracking effort, as the sealing portion of the seat "backs away" from the orifice. So for the shop, they'd rather give you a hard-breathing reg for a few months, knowing that its characteristics will improve a bit as the seat takes a set, than give you a reg that breathes perfectly, and have you come in three months later, unhappy that your second stage is freeflowing a little.
Most divers don't know what to ask for, and if your set is stiff, an adjustment of cracking effort will take about three minutes.
To confirm that IP is not the driver of ease of breathing, ask any ice diver. They set their IP's VERY low to prevent freezing up. And they can have any ease of breathing they want by tweaking their second stage. That is even true of unbalanced second stages, though it's a little harder to keep them right where you want them as the seat ages.

 

[Ojai Diver]

He did make adjustments to the second stage itself, which helped, but also adjusted the IP. I do not know the numbers, but I believe he increased it. It does breathes better than it did.

Does cracking pressure have a unit? I thought he said it was "1.1" before adjustment. Or is that number for breathing resistance? Thanks.

 

[fmerkel]

+ @rsingler.
With an IP gauge and a tiny bit of knowledge you can tweak them yourself. If the 1st stage IP is in spec and not creeping....leave it alone, it's fine. Then learn to adjust the 2nd stage. It's easy. Maybe your tech will even show you so you quit annoying him.

 

[Couv]

Does cracking pressure have a unit? I thought he said it was "1.1" before adjustment.

Pressure is sometimes measured in inches of water. Usually it is a differential pressure measurement. So, your second stage had a cracking effort of 1.1 inches of water above ambient. Actually not too bad, but more than what most of us who DIY would consider an easy breather. My Argonaut Kraken has a cracking effort of 0.5 inches, and most of my BA/G250/109s crack at 0.75 inches. Your tech is probably correct that it was in spec. For instance, SP specs for a G260 is 1.1 to 1.2 inches.

 

[Ojai Diver]

Then learn to adjust the 2nd stage.

Ultimately, I agree.

Pressure is sometimes measured in inches of water. Usually it is a differential pressure measurement. So, your second stage had a cracking effort of 1.1 inches of water above ambient. Actually not too bad, but more than what most of us who DIY would consider an easy breather. My Argonaut Kraken has a cracking effort of 0.5 inches, and most of my BA/G250/109s crack at 0.75 inches. Your tech is probably correct that it was in spec. For instance, SP specs for a G260 is 1.1 to 1.2 inches.

Interesting. So for the G260 above (for example) are you saying it can be adjusted to less cracking effort than its specs? If so, why would a tech be reluctant to do so? Are they obliged to deliver in spec? Or is there some performance trade off?

 

[Couv]

Interesting. So for the G260 above (for example) are you saying it can be adjusted to less cracking effort than its specs?

Yes

If so, why would a tech be reluctant to do so?

Well, if that's the manufactures recommendation, and he/she is working in a sponsored shop he/she pretty is much is bound by the manual's specs. Besides, once it falls in the specs he can be lazy and stop the tuning process. As pointed out by a previous poster, this makes sense for a shop as the customer is more likely to bring back a freeflowing second stage than one that breathes on the hard side.

Why not tell us what second stage you have. If there is a simple adjustment one of us may be able to advise you. (we promise not to tell the LDS or the manufacturer) Better yet, join us in the DIY section and forget about taking your reg in for un-needed service.

 

[fmerkel]

Read the response by rsingler...again, carefully. He explains it quite well.
Cracking pressure is just that, the amount of effort it takes to START the flow. Depending on the reg once started, with no resistance, the reg may free flow. Most high performance regs will do this. Its a design to lower WOB. The lower the cracking pressure, the more likely to free flow. It's a bit of a trade off.

I've 'fixed' quite a few regs that just came back from servicing with the leak issue. Of course the diver is upset. "I just had [name the shop] over haul this and it's worse than when I took it in".
1/16 turn on the 2nd stage and the problem is fixed.
Most divers don't know how their regs work. Shops and the dive educational system does not teach it. You have to dig that out for yourself.

Note - I always check 1st stage IP before messing with someone 2nd stage tuning. I've sent a few divers home with servicing needed for their regs. This has not been on regs just serviced. Often it's regs that have been sitting around awhile.

 

[rsingler]

The reason the G260 has a min cracking effort of 1.1" is due to a factor known as "case geometry fault".
Briefly, because the G250/260 case is so large, in certain positions (head moderately down) the center of the diaphragm can be lower than 1.1" below the top edge of the exhalation valve. If the cracking effort is adjusted lower than that, the reg will freeflow slightly, which is discomfiting to some divers.
Actually, factory spec is rarely less than 1.1" for most second stages. Those of us who go lighter deal with freeflow by a slight counter effort in those positions, in exchange for easier breathing in the rest.
That's a discussion you will have to have with your tech, who may or may not be willing to adjust outside specification.
I'll try to post a link to previous discussions on case geometry.