Diving Depth Gauge

Make a simple depth gauge for freediving out of a syringe. This is also an experiment with Boyle's law which states that the product of the pressure and the volume of an ideal gas is constant.

Step 1 Materials

You need one syringe, one zip tie, a marker pen and a knife.
Preferably the syringe should be large and have a scale with divisions to sixty.

Comments

[sj14]

Can you please tell me the formula to work out the depth marks.thanks

[khogan2]

Thanks . Ill build one for my under water video camera. Its only goes down to 16 feet for snorkeling. Hopefully the pet store will have a syringe for sale , or Ill just have to find a dead junky in some back alley . lol

[zerrodach]

I have a 20 ml syringe. How many feet is 5 ml? 10 ml? How could I figure it out without testing it? Thanks for any help.

[Aleksi]

Pressure p = volume at surface / compressed volume.
Depth in meters = (p-1)*10
For 20ml at surface pressure you get 15ml at 10 feet and 10ml at 33 feet. I guess you don't need a mark at 5ml. The 20ml syringe will not be very accurate.

[engineer_01]

wont water go into the hole?

[stuffman366]

No, because the plunger is below the hole. The hole is opposite the sealed end and you push the plunger just past the hole into the body of the syringe.

[rbotes]

Thanks Aleksi, we had great fun taking this baby to depth! Spot on at 20m, and think it was pretty much there at 30m as well (but to be honest i was thinking more about my chest squeeze than the gauge at 30m!) Version 2 to have some kind of max depth indicator to check once back on the surface? Maybe a movable O-ring inside?

[Aleksi]

Nice! I only went to 25m and then my ears were telling me to stop. The chest squeeze gets uncomfortable too. To record the maximum depth, you could add a valve which lets the air out when you ascend. The piston would then hopefully stay at the maximum reading. Have you got any ideas for making this instrument more wearable?

[jconrad66]

Dont you equalize your ear tubes whilst diving by pinching nostrils and blowing air to "clear " your ears? Saved my ears for years, specially whilst scuba diving.

[Aleksi]

The technique you described only works if you have an excess of air (which you have when scuba diving). For a freediver it is more difficult because at -25m the air in his lungs has been compressed to one third of its surface volume. This is what rbotes means by chest squeeze. It occurs at about -30m and beyond this depth it is practically impossible to blow out any more air from the lungs. I would need to learn a more advanced technique, like e.g. the frenzel-fattah equalisation technique if I wanted to go deeper.

[rbotes]

hmm, good idea on the valve, will try and think of a nice way to do this. In terms of "wearability" I was thinking of removing the side wings and cutting off as much of the plunger arm as possible, then inserting into a simple neoprene cover that can be slipped over the forearm. A smaller syringe would be good too but I guess you'd loose too much accuracy?

[reis123]

I think you must do a video to show us how to perform it ! Thank You :)

[roban]

Have you tried this out at depth? How well does it perform? Any problems from the friction on the plunger?

[fester.gump]

Interesting. Is any temperature drop noticable? Buoyancy experiments would be fun to try.

[Aleksi]

I haven't noticed any. Next time I'll check for condensation.

[Matt23]

this is really cool i have to try to build this to use when i go snorkeling