Safe to deliberately cause a free-flow reg?

[DeaDLocK]

Hey all,

I have purchased a new rig (my first), and am planning to take it to the pool in the next few days to test everything out.

As part of this process, at the end of my session, I am planning to empty the tank down to around 100psi so I can do proper weighting checks (I often do very long dives at very shallow depths - around 4 to 5 metres - and run the tank down to very low pressures and then just end the dive by surfacing, so I need to test to ensure I am weighted enough to stay down in those circumstances).

To do this, I guess I will just hold down the purge on my brand new reg until the pressure drops to the correct level. Just checking to see that this won't damage the reg in any way!

I will of course see if my LDS has any spent tanks first, but if they don't, it should be safe for me to empty a full tank down to nearly nothing my purging on my reg, right?

I will also of course make sure to keep some pressure in there to keep contaminants out.

Thanks!

 

[rstofer]

I wouldn't do it that way even if the regulator could handle it. Why not just detach the regulator and vernt the tank. Sure, you won't have a pressure gauge but it takes a long time to drain a tank. I might stop after a few minutes, reconnect the reg and check the pressure. Then I would have some idea how long the next interval should be. The shop is bound to have a tank pressure gauge.

Richard

 

[herman]

No problem at all. The only place where an extended freeflow can cause problems is in cold water where the reg internals may freeze.....I am guessing your pool is not less than 50 deg .

By the way, 500-600 psi is fine, not likely the few extra ounces will make any real difference in your weighting.

 

[*dave*]

No, you won't damage it. The worst that could happen is freezing the first stage and bleeding the tank dry before you can shut down the valve.

I'd recommend bleeding down to 500 psi and doing a weight check in 5'(1-2m). If you can hold 5'@500psi, you're golden.

 

[DeaDLocK]

No risk of freezing - more a risk of sunburn! I'm in Malaysia.

Also, I'm 5" 10', 185lbs. Once I have my correct weighting in the pool with a 3mm suit, can any of you take a rough stab as to how much more weight I'll have to add for salty diving?

Thanks!

 

[SteveAD]

freeflow will be no problem. the only problem with your idea is that a perfect weight check in a pool does not equate to perfect weighting in the real world (assuming you ae diving in the ocean)

 

[LeadTurn_SD]

freeflow will be no problem. the only problem with your idea is that a perfect weight check in a pool does not equate to perfect weighting in the real world (assuming you ae diving in the ocean)

1+

DeaDLocK: It is great that you are doing this to get your buoyancy dailed in, but going from fresh to salt water or vice versa will always result in a ballpark "best guess" at weighting, then you'll almost always need to repeat the test once in the ocean to get it exactly right.

300-500 lbs is fine to test weighting. I don't recommend 100lbs, mostly for the slight safety concern that your SPG may not be 100% accurate at the end ranges (although this is a pretty minor concern with what your doing).

Best wishes.

 

[Bubbletrubble]

Also, I'm 5" 10', 185lbs. Once I have my correct weighting in the pool with a 3mm suit, can any of you take a rough stab as to how much more weight I'll have to add for salty diving?

@DeaDLocK: Add 2.5% of your total weight (you + rig) to convert from fresh water to salt water.
For instance, you weigh 185 lbs. If your rig weighs 40 lbs. (dry weight), then your total weight is 225 lbs. 2.5% of 225 lbs. is about 5.6 lbs. Adding 6 lbs. would be appropriate.

This should get you very close to your weighting needs in salt water. As others have recommended, there's no substitute for doing a proper weight check under the conditions in which you'll be diving.

FWIW, you don't really need to bleed your tank down to 500 psi (or less) to do a proper weight check. Just do a regular weight check with a completely full tank...then consult a tank specs chart to find out the buoyancy swing of the brand/size tank. Use the buoyancy swing to calculate how much extra weight you'll need to compensate for a near empty tank.
For instance, using a full Catalina S80 aluminum tank + the rest of your rig, let's say you needed 5 lbs. of lead. Consulting a tank specs chart, you see that a Catalina S80 is -1.8 lbs. buoyant (when full) and +4 lbs. buoyant (when empty). Given this info for an empty tank, you would need roughly 5 lbs. of additional lead to compensate for the loss of ballast in your tank (going from full to about 500psi). Thus, your total weight requirement would be 5 + 5 = 10 lbs. If you prefer to weight yourself for a completely empty tank, then add an extra lb. of lead.

Hope this info helps...

 

[fnfalman]

I would not bleed a tank down to 100-psi. That's way too low for safety concerns. 500-psi is plenty light for weight check yet still has enough reserve for oops. Besides, in the real world, you should be planning on surfacing with about 500-psi in your tank anyway.

And performing a weight check with a full tank is fine too and it comes pretty darn close to performing a weight check with a near empty tank.

 

[herman]

I would not bleed a tank down to 100-psi. That's way too low for safety concerns. 500-psi is plenty light for weight check yet still has enough reserve for oops. Besides, in the real world, you should be planning on surfacing with about 500-psi in your tank anyway.

And performing a weight check with a full tank is fine too and it comes pretty darn close to performing a weight check with a near empty tank.

There is no safety concern, he is in a pool , just stand up if you run out of air, still no need to go that low.

There is around 5lbs of shift in an 80 from full to 500psi. If the objective is to correctly weight yourself, you must either add that 5 lbs to your total or deal with being light at the end of the dive if you do your weight checks with a full tank. If you do not add that weight back in you will be 5lbs light at the end of the dive. I can deal with that much underweighting but it's a pain. My weighting requirements are a lot more critical than that of most divers because I dive without a BC a lot of the time so my weighting has to be dead on. For no BC diving, I weight so I am as close as possible to dead on neutral at 1/2 tank pressure and use lung volume to deal with the slight over/under weighting at the ends of the dive. I use 1/2 pound weights to get the weight as close as possible. Another reason to weight with a drained tank or more properly at the end of a dive is to make sure all the trapped air has been gotten out of your exposure protection and BC.

The 2.5% difference in fresh and salt water seems to be about right for me, I get about 5 lbs doing the math and my actual is 4, YRMV.