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View Full Version : Accurate SPG? Who makes one?



mksmith713
02-25-2009, 09:47
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
02-25-2009, 10:22
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
02-25-2009, 10:47
YouTube - making a scuba pressure gauge or SPG (http://www.youtube.com/watch?v=djNB4Hluj1E)

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

bubbletrubble
02-25-2009, 10:58
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
02-25-2009, 11:07
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
02-25-2009, 11:31
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.


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
02-25-2009, 11:43
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
02-25-2009, 12:59
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
02-25-2009, 13:10
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
02-25-2009, 13:36
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?

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.

mksmith713
02-25-2009, 14:07
I remember back, before I knew any of this stuff about inaccurate SPG's.
I did one of my dives for AOW and I breathed my tank down to 50 psi.
Granted,it wasn't a very deep dive, maybe 40 ft (I think it was either Nav or bouyancy control dive) and I did 3 minutes at 15 ft and some refresher stuff at shallow depths as well.
Still, that would have been a lesson to remember.
I didn't sling a pony back then.

bubbletrubble
02-25-2009, 14:41
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?

@mksmith713: I hear ya. You want your family to be using safe gear. I think we all feel the same way. Diving is a risky sport. Many things can go wrong.

Considering your family's diving habits, SPG accuracy is a minor contributing factor to overall safety. But if it makes you feel any better, then go ahead and spend $10-$20/spg (or whatever your LDS charges) to do a rigorous pressure check. I submit that they would be far better served spending that money on optimizing buoyancy/trim skills, staying in good physical fitness, practicing good buddy skills (pre-dive checks, air shares, etc.), and getting some instruction with a dive professional.

If your family is only doing 1 or 2 dive vacations a year, then please have them take refresher courses and do some pool practice before your next trip as CompuDude suggests.

Straegen
02-25-2009, 15:21
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."

The manufacturers I believe are all the same company in Italy, but I could be wrong. I believe they are 99% mechanically the same either way.

For me what defines a quality guage is a brass gauge with tempered glass with a good reputation. Quality is going to mean different things to different people, but that is how I would define it.

My SPGs had an informal test against shop gauges. They were tested at various psi readings. It only took a couple minutes and the shop didn't mind doing it for me. I could bench test them as I know someone with the proper gear, but I don't think it is necessary.

Cost was free and there were no specs. I just wanted to make sure my gauges matched or were close to known values. I am not interested in knowing the exact PSI just need to know the gauge is close especially at the lower points.

RMur
02-25-2009, 15:31
I would expect SPGs to exhibit some natural hysteresis and therefore would tend to be more accurate at the top end, and less accurate as the tank is breathed down.

Had to say how linear the hysteresis might be.

mksmith713
02-25-2009, 15:33
I would think HOG guages would be high on the list of quality since the DIR guys love them but I read in another post where a few people had HOG SPG's flooded on the first dive.
Not as much a question of accuracy as it is with craftsmanship or quality control.
Sure, they sent them back for free replacement but what a pain in the @ss to have it flood on your first dive of a dive vacation somewhere exotic and far away and expensive to get to.

If I'm going away on a dive vacation, I take my own gear because I WANT TO DIVE MY OWN GEAR.
I'm obviously comfortable with it. I know it and I trust it.
If I have to RENT gear from a dive operator because my brand new SPG floods and I have no back up SPG, that would SUCK.

BouzoukiJoe A.K.A. wrecker130 AKA Chuck Norris AKA joeforbroke (banned)
02-25-2009, 15:50
I would expect SPGs to exhibit some natural hysteresis and therefore would tend to be more accurate at the top end, and less accurate as the tank is breathed down.

Had to say how linear the hysteresis might be.

No fair bringing physics into this argument. This is an internet dive forum after all :smiley2: