Intermediate Pressure Guage

[Quero]

Yo, any mods awake? How many times can I "like" a post???

Once. (Unless you "unlike" it and then "like" it again, and then "unlike" it, and so on. In that case, it's a question of how fast your connection is and how much time you've got on your hands. We don't have a gauge to track this, so there's no such thing as "like creep".)

 

[Luis H]

Not unless they have:
1. A submersible IP gauge
2. A place to plug it in without disabling the inflator
3. A very techno-geek attitude that would result in having more interest in your reg's IP than the dive itself.

Now, if someone did manage to check off those requirements and dive with an IP gauge connected, they'd get some interesting info. First, absolute IP rises so that it maintains a constant level above ambient pressure, so the gauge 'should' show, for example, 130 at the surface, 145 at 33ft, 160 at 66ft, etc.....but I'm not sure if a regular IP gauge reads pressure in relation to ambient. Interesting to see how that would go, I suspect someone else would have a better idea than I. Another interesting thing to see would be the amount of IP drop and rate of recovery as depth increases. The 1st stage is working harder to maintain flow at the higher IP and ambient pressures as depth increases. My guess is that a entry level, lower performing 1st would start to show more serious IP drop during demand and slower recovery. I bet a high performing balanced piston like the MK20/25 or atomic would show essentially zero difference in IP drop at anything like recreational depths.

Since you're an engineer, I nominate you to try this experiment and video record it!

Most IP gauges would flood and you would be measuring pressure differential to ambient (not to 1 atm).

I have been meaning to do it, but I haven't yet.

 

[koozemani]

Great thread!

 

[halocline]

Yeah, sort of.

Meaning: It is useful to not only track the creep, but to be able to tell the reg rebuilders where you want your IP set and why.

Being a cold water diver, I like my IP set about midrange with the secondaries set "normal".

It is an old school idea to set IP low for cold water use, with the thought that it reduces flow to the 2nd stage, and it does do that, especially with not-so-high flow 1st stages. It really matters with unbalanced 2nds, but with high-flow 1sts (like the MK25) and balanced 2nds I suspect it doesn;t make too much difference in freezing. Interestingly, a lower IP actually increases adiabatic cooling (theoretically) at the 1st stage, where most of the freezing is likely to occur. How much difference that would make in a real-world scenario I have no idea.

I set mine pretty low too; around 125 for the MK5s. They seem to stay there forever. IP is a little like blood pressure; it's much more likely to go up than down. The 2nd stages I use are all balanced and they work fine with a nice low IP.

The IP gauge tells you how the 1st stage is functioning overall; how quickly it recovers, how stable it is with regards to varying tank pressure and different kinds of demands. The only thing that the cheap IP gauges mounted in the LP inflator hose doesn't read well (IMO) is the type of dynamic drop in IP. I assume that's because there are venturi forces in the hoses that drop pressure in the inflator hose in the presence of fast moving air in the other hoses.

 

[chrpai]

It is an old school idea to set IP low for cold water use, with the thought that it reduces flow to the 2nd stage, and it does do that, especially with not-so-high flow 1st stages. It really matters with unbalanced 2nds, but with high-flow 1sts (like the MK25) and balanced 2nds I suspect it doesn;t make too much difference in freezing. Interestingly, a lower IP actually increases adiabatic cooling (theoretically) at the 1st stage, where most of the freezing is likely to occur. How much difference that would make in a real-world scenario I have no idea.

Part of that old school idea was to also have an unbalanced 2nd stage as your secondary regulator.

 

[lowviz]

...//... I set mine pretty low too; around 125 for the MK5s. They seem to stay there forever. ...//... The 2nd stages I use are all balanced and they work fine with a nice low IP. ...//...

That's close to mine. The IP holds at 110 during a venturi free-flow so I'm guessing that an MK17 easily qualifies as a high-flow reg (it is well known that the MK25 is legendary in the high-flow category). My second stage is a G250...

 

[SeaCobra]

This is one of those things that I think every diver should understand and have one in his save a dive kit. And yet you rarely see an LDS carry it. I have my theories on why but I'll stop there.

I can answer that as I used to manage a dive center, that is now a pretty good player in the online sales arena, and we stocked those IP gauges. Rarely sold any, and when we did it was usually to staff or a local instructor. Now I own a dive center and I do not stock these gauges. Why? Because no one ever asks for one. I demonstrate their use and value in my Advanced and Master diver classes, as well as Leadership, and use it at my local dive sites. Yet no one asks for one.

 

[lowviz]

IMHO, If you want an IP gauge, buy one that won't annoy you for anything other than quick checks.

 

[redacted]

Such gauges tend to be most accurate mid-scale. All my IP gauges are 0 to 300 psi. Good quality gauges can be found at very reasonable prices ($15). A scuba adapter will run another $10.

 

[lowviz]

It was a toss-up (to me) between wider spacing on the dial and mid-range accuracy.

I'm curious about the response times for liquid-filled ones.