Cracking pressure?

[chace_nicole]

I know I could call the guys at ST and get an answer to this, but I thought...if I'm wondering...maybe others are too.

I recently had a my regs serviced and received a report with them stating serial numbers and cracking pressures.

I know that if things needed repair that they would call me, its just that I do not know what these numbers mean. Is a certain cracking pressure better or worse? Any insight would be appreciated.

[burna]

I'm certainly no guru on the subject, but I think the numbers refer to the depth of water the reg (with mouthpiece facing upwards) has to submerged before the air starts to flow.

Try here for more info.
SCUBA REG MAINTENANCE AND REPAIR Excerpts

You can see it for yourself by hooking your regs to a cylinder and gently start submerging the second stage into a bucket of water.

Hope this helps, maybe others can provide more.

edit. Oh look, it's even got a picture down the bottom, I didn't scroll down that far.

[awap]

Cracking pressure is usually measured in units of inches of water. This measurement, BTW, is the distance the diaphragm must be submerged in water to unseat the valve and start the flow of gas. Few if any regulators can achieve stable cracking pressures of less than 0.6 inches. Some high performance regulators can be tuned to work in the range of 0.6 to 1.0 inches but may be subject to freeflow problems if they do not have a user cracking pressure adjustment knob. Generally most good 2nds are set in the range of 1.0 to 1.4 inches and should provide satisfactory performance. On most 2nds, the distance from the diaphragm to the mouthpiece is 2.0 to 2.5 inches or a bit more. Alternate 2nds may be tuned with higher cracking pressures, in the 1.2 to 1.6 inch range, to reduce freeflow problems. If cracking pressure is 2.0 inches or more, most divers will feel the reg is uncomfortably hard breathing.

Cracking pressure will often change over time and usage as parts wear and take a set. I set most of my regs right around the 1.0 inch mark (eyeballed in a sink of water, no fancy gauge) and then go back to the sink every couple months and check and tweak them as necessary.

[chace_nicole]

Thank you both for the info

[Crimediver]

Cracking pressure refers to the PSI exerted on your body when doing extremely deep dives. You know when this occurs as your lungs have become compressed to the size of a raisin and your tidal volume is approx .3 cm. Descending even a millimeter deeper causes your body to implode into your cranium and your scream will be sucked into your sinus so rapidly it will cause a small flash of fire from the heat.

[chace_nicole]

Originally Posted by Crimediver

Cracking pressure refers to the PSI exerted on your body when doing extremely deep dives. You know when this occurs as your lungs have become compressed to the size of a raisin and your tidal volume is approx .3 cm. Descending even a millimeter deeper causes your body to implode into your cranium and your scream will be sucked into your sinus so rapidly it will cause a small flash of fire from the heat.