Button Pressure Gauge. Is it safe?

[Kharon]

Does this mean that the button gauges do not have a vent valve on the back (or maybe side)?

Not that I know of. But none of my SPG's do, no matter what the size. Are you thinking of the burst disk on a valve?

 

[2airishuman]

All button pressure gauges aren't the same. There are several styles with differing amounts of needle travel, making some easier to read than others.

I have several, and use them on stage bottles and on J-valve rigs. In both cases the purpose is to verify that a cylinder is full before diving.

I check them for accuracy when new, and have had to send one or two of them back.

 

[stuartv]

I have a couple of these:

Mini-SPG, { 1 in | 2.5 cm } Face

I use one on my single tank reg set and one on my deco bottle reg. For single tank, an AI computer is what tells me my tank pressure during the dive. The button gauge on the 1st stage is just so I can see "full or not full" when I put the reg on a tank without having to get out my computer. My deco bottle reg has one, again, just so I can easily confirm "full or not full" when I check it. I don't ever need to know the exact pressure in the deco bottle. It just needs to full (or pretty close) when I start a dive.

The body on these DGX gauges is metal. The face is polycarbonate. I'm not particularly worried about one blowing up and ruining a dive.

 

[KeithG]

Not that I know of. But none of my SPG's do, no matter what the size. Are you thinking of the burst disk on a valve?

Not a burst disk, but it serves a similar purpose.

My terminology may be incorrect. Maybe I should be calling it a safety vent or a 1 way safety valve?

It was explained to me like this: if the bourdon tube breaks, then high pressure air will build up inside the sealed case of the pressure gauge. The gauge casing is not designed to handle this pressure. So a 1 way vent is added to the back of the gauge case to allow the pressure to escape so that the pressure gauge does not explode. The excess air vents out the back, preventing the faceplate from being blown off and potentially injuring a person looking at the gauge.

My google-fu is not working very well as i can not find any reliable reference to support this old wives tail.

 

[tbone1004]

Not a burst disk, but it serves a similar purpose.

My terminology may be incorrect. Maybe I should be calling it a safety vent or a 1 way safety valve?

It was explained to me like this: if the bourdon tube breaks, then high pressure air will build up inside the sealed case of the pressure gauge. The gauge casing is not designed to handle this pressure. So a 1 way vent is added to the back of the gauge case to allow the pressure to escape so that the pressure gauge does not explode. The excess air vents out the back, preventing the faceplate from being blown off and potentially injuring a person looking at the gauge.

My google-fu is not working very well as i can not find any reliable reference to support this old wives tail.

all spg's should have them. This picture is from Termo's website *dude's who make basically all scuba SPG's*. You can see on the back side of the spg a little black dot. That black dot is the safety plug

 

[Kharon]

Not a burst disk, but it serves a similar purpose.

My terminology may be incorrect. Maybe I should be calling it a safety vent or a 1 way safety valve?

It was explained to me like this: if the bourdon tube breaks, then high pressure air will build up inside the sealed case of the pressure gauge. The gauge casing is not designed to handle this pressure. So a 1 way vent is added to the back of the gauge case to allow the pressure to escape so that the pressure gauge does not explode. The excess air vents out the back, preventing the faceplate from being blown off and potentially injuring a person looking at the gauge.

My google-fu is not working very well as i can not find any reliable reference to support this old wives tail.

First I've heard of this. I can't find anything that looks like that on any of my SPG's. Maybe on high end SPG's?

 

[kelemvor]

There is definitely a vent on all of my gauges. My full size gauges are highland branded and my button gauge that I use on a deco bottle is diverite branded. Here's a photo of the one on the diverite button gauge.

For what it's worth, I think this one is going on 3 years old now, so I must be overdue for a failure. When it goes, I guess that's another $23 down the tubes... actually, I probably paid $50 at my LDS last time.

If you guys aren't finding it on your button gauge, mine was hidden on the underside of the gauge. I had to turn the bottle upside down in order to see the hole with the reg attached to the bottle.

 

[Kharon]

I just checked 2 buttons and one regular size SPG's - all H2Odyssey. None have the dot on the back.

 

[kelemvor]

In that case, while there may or may not be multiple manufacturers there are definitely different designs. Moreover, the designs differ in ways other than purely cosmetic.

My google-fu isn't the best but it looks to me like the h2odyssey can be had for around $25 and the diverite is $27 (the $23 price was for BAR). Maybe try a diverite the next time your button gauge fails?

I would bet this accounts for the differences of opinion regarding reliability of button gauges in this thread.

 

[redacted]

Without a safe way to relieve pressure in the event of an internal failure, an SPG could be a hazard. I'm betting thyere is a little relief plug somewhere.