SW vs FW Pressure Gauges

[Tickler]

SW exerts more pressure than FW does which is why an atmosphere of SW is slightly less than than an atmosphere of FW. If this is the case then do pressure gauges give slightly different depth readings for these different environments?

Just something that I am curious about.

 

[GrumpyOldGuy]

A traditional pressure gauge (bourdon tube) will register the difference in pressure between the tank and the environment. So it will change FW vs. SW and also change with depth since the environmental pressure will change. The magnitude of the change at depth is very small relative to the tank pressure, 60PSI at 120ft vs 3000PSI, so I doubt you would notice. The difference between FW and SW is only 2.5% of that, which is only about 1PSI.

 

[tahqa]

There is an older discussion of this topic located here: http://www.scubaboard.com/forums/ne.../259432-diving-salt-water-vs-fresh-water.html

 

[mala]

they do

the temp of the water effects density and of course not all sea water has the same composition.
gravity varies slightly depending on where you are on the planet.

very curious indeed

 

[Michael Guerrero]

Tickler, do you mean depth gauge? You said pressure gauge, which in typical dive parlance means the gauge attached to your scuba cylinder which measures the amount of pressure in the tank. Hence Grumpy's response.

 

[Tickler]

Sorry, I did mean depth gauge. My bad. Thank you for catching that one.

 

[dumpsterDiver]

SW exerts more pressure than FW does which is why an atmosphere of SW is slightly less than than an atmosphere of FW. If this is the case then do pressure gauges give slightly different depth readings for these different environments?

Just something that I am curious about.

depth gauges measure pressure, not distance from the gauge to the surface. So 33 feet on a depth gauge means you have to swim 34 feet to the surface in freshwater... not something that matters in recreational diving.

 

[Michael Guerrero]

Yes. This is why computers have fresh and salt water settings.