Accurate SPG? Who makes one?

[mksmith713]

A spin off of another thread I started.
Please feel free to chime in with your opinions on who makes the most accurate SPG.
I couldn't believe the disparity in my SPG's.
They ranged from 2500 psi to 3000 psi during my tests.
Perhaps I need to replace all of my SPG's with ones that are dead on balls accurate.
So, who makes the most accurate SPG.

[Straegen]

I think most brass and glass gauges mostly come from the same place and are reasonably accurate. The more use a gauge gets by its design the less accurate it will probably become. I think buying a quality gauge and keeping it tested is a good idea based on the numbers from your other thread. I would even go so far as to say it is a good idea to test out a newly purchased one.

[mksmith713]

YouTube - making a scuba pressure gauge or SPG

After watching this, you'd think if everyone who manufactured a SPG made them this way, they'd all be accurate.

[bubbletrubble]

Hmmm. Ask any experienced diver how often he "tests" his SPG. :-)

All of the SPGs used for SCUBA (that I know of) are based on a bourdon tube design. I suppose that the coiled tube mechanism (or the linkage to the gear train or the needle) may wear out or fail over time. However, it's a pretty reliable design.

Straegen, I'm just curious. How many SPGs do you own? What brand(s) are they? What do you deem a "quality" gauge? How many times have you gotten each of them calibrated? I'm sure that many reg repair shops perform some cursory testing of the SPGs during annual reg servicing. That's probably good enough for most people. Personally, I have never seen a need to get a rigorous calibration done on any of my SPGs. YMMV.

I think you guys are blowing this thing waaaaay out of proportion if you insist that your SPG be "dead on balls accurate."

[acamato]

It would be nice if the SCUBA manufaturers published their accuracy specs. I know that if you purchase a gauge from a known manufacturer (Ashcroft, Wika) they will provide you with the specs.

What is special about a SCUBA spg? why cant someone buy one from a gauge manufacturer and put an adpater on the gauge for the hose? Something I wil have to look into.

[Straegen]

Originally Posted by bubbletrubble

I'm just curious. How many SPGs do you own? What brand(s) are they? What do you deem a "quality" gauge? How many times have you gotten each of them calibrated? I'm sure that many reg repair shops perform some cursory testing of the SPGs during annual reg servicing. That's probably good enough for most people. Personally, I have never seen a need to get a rigorous calibration done on any of my SPGs. YMMV.

I have four. One OMS 52mm, one Oxycheq 2" and two Highland Millworks 2.5". Two were tested a few weeks ago and the other two are headed in for a test first week in March as they are new.

Originally Posted by bubbletrubble

I think you guys are blowing this thing waaaaay out of proportion if you insist that your SPG be "dead on balls accurate."

I don't think they need to be spot on and I stated earlier that I think they would be fine as I am guessing they are off in a linear fashion rather than a progressive one simply meaning the closer you get to 0 the more accurate they become.

That aside if I had a gauge showing a near 17% margin of error, I would consider it time to retire that SPG. That is my personal opinion and not some hard rule. I am sure the gauge will continue to work fine for years to come, but for $100 why bother risk a trip on a gauge that is already showing signs of wear and/or damage.

[bubbletrubble]

Originally Posted by Straegen

I have four. One OMS 52mm, one Oxycheq 2" and two Highland Millworks 2.5". Two were tested a few weeks ago and the other two are headed in for a test first week in March as they are new.

@Straegen: Thanks for answering my questions. I have a few more:
Are you aware of which company actually manufactures the gauges you own?
Who makes a "quality" gauge?
What specific type of testing is being done on your SPGs?
What kind of "specs" are you given at the end of testing?
How much does the testing cost per gauge?
Just curious. As I said before, I've never gotten any of my SPGs "tested."

[CompuDude]

I've never formally tested any of my gauges, either. I know they're within a couple hundred PSI of the shop's wall gauge, and their tester gauge, and MY tester gauge, and there's little difference that I've noted on the rare occasion that I hook up one set of regs and switch to another. There usually is a difference in going from my computer (wireless transmitter) to my SPG, but that's easily attributable to the way the computer "corrects" for temp. Annoying, but I'm quite used to the disparity and would notice if there was change in the normal pattern.

The "testing" that I've done is sucked my tanks down quite low during shore dives at a certain sheltered location where the last 20 minutes of the dive is in 15 of water. Exiting with 200 psi or so, below the ability of the computer and PSI gauge to properly register pressure, and I'm still breathing. Frankly, that tells me all I need to know about my gauges. Sort of like running out of gas... until you actually see where the needle is when you run out of gas on the freeway, you never know exactly where true "empty" is.

As long as you know where true empty is, and you know how to guestimate your true expected rate of consumption through experience with a given set of gear, does it really matter if the gauge matches up with some laboratory specification for accuracy?

[mksmith713]

Originally Posted by CompuDude

As long as you know where true empty is, and you know how to guestimate your true expected rate of consumption through experience with a given set of gear, does it really matter if the gauge matches up with some laboratory specification for accuracy?

That's all well and good for someone who dives regularly.
But what about my wife and kids who might do 2 trips for a total of 10 dives a year?
They're not going to be in tune with their gear as much as someone who dives 100 or more times a year.

I can see my wife now....,"Honey, I can't remember....was my guage 100 psi off or 1000 psi off?

[CompuDude]

Originally Posted by mksmith713

That's all well and good for someone who dives regularly.
But what about my wife and kids who might do 2 trips for a total of 10 dives a year?
They're not going to be in tune with their gear as much as someone who dives 100 or more times a year.

I can see my wife now....,"Honey, I can't remember....was my guage 100 psi off or 1000 psi off?

I'll grant you that. Might do well to dive their gear periodically and make sure it's performing well enough, if you're going to let it go that long between dives. Of course, going that long between dives, you're supposed to do a refresher of some sort (or at least a gear check dive in easy conditions, be it sheltered bay or pool) before hitting a "real" dive, anyway.

The top end truly doesn't matter, as long the lower end is accurate enough (by which I mean you can breathe the tank down to 200-300 psi and there is still gas in the tank) and the movement towards the low end is consistent. Diving that infrequently, they're not going to have a feel for their consumption rate and will need to be referencing the SPG frequently anyway. Remember, the top end going to vary wildly from fill to fill anyway, depending on who filled the tank, to what level, how fast the fill was, etc. That's always going to vary from dive to dive unless you have some outfit cranking out precise fills tank after tank. (I've never seen this in over 20 years of diving.) The lower end what matters most.