Weight/buoyancy of tank valve

[Divectionist]

Hi

the buoyancy specs I can find for my pony bottle refer to the empty/full weight excluding the valve.

does anyone know the approximate buoyancy, or just dry weight as it will be very similar, of a tank valve (mine is a 232 bar Faber). Shop websites don't seem to bother with weight specs for valves.

I'd like to get the buoyancy of the pony assembly calculated as closely as possible, accounting for the valve and reg also.

Appreciated!

 

[michael-fisch]

around 400g +-50g

Michael

 

[Divectionist]

Thanks!

 

[Zef]

The buoyancy of the object is directly correlated to the volume of the object.

To compute the volume: measure the weight of the object (in Kilograms) out of the water, and then measure the weight of the object (in KGs) in the water. The Difference between the two is the volume of the displace water and this is directly correlated to the volume of the object.

For conversions:
1 Liter of fresh water is approximately 1 KG
1 KG is approximately 2.2 Lbs.

If you have the valve separate from the cylinder you can weight just that or if it is attached to the cylinder do the calculations above for the cylinder and valve and then subtract the value you have for the buoyancy of the cylinder to compute the value for the valve.

-Z

 

[Divectionist]

That's right Zef, just can't perform the measurements now so I need a theoretical value to leave some best guess amount of lead on the boat for the first dive with the new equipment. With the dense valve weighing in at approx. 1lbs that is a significant enough difference to the whole package.

I am basically running on the following assumption now:
Pony -2.4lbs (actually likely a bit heavier due to the Australian standard vs US specs but I got no specifics)
DIN 232 Valve -1lbs
MK2 First stage -1lbs (second stage just goes from primary to pony reg so not accounted for)
= -4.4lbs buoyancy with a full bottle

I'll remove 3lbs from my left side hip pocket and left side cam band to start with and see how it goes.

I went unorthodox with a 2l/16cuft HP steel pony instead of alu, mostly for solo diving, so handing it off and becoming excessively light underwater is not a main factor, but it gives me more ditchable weight at the surface and reduces half the (previously unditchable) lead I carry. I hope that slinging it on the left balances out well with the remaining lead all on the right side of my body.

 

[Zef]

About 2 months ago I started diving with a 3L steel pony bottle. I clip it to my left shoulder D-ring and the tail end gets clipped to the d-ring on the rear of my crotch strap. I have found that I could drop a kilo or so of lead when I am diving the pony bottle but I have not focused on reducing lead from one side as I have not had any problems with the tank causing me to roll to one side.

My plate is stainless steel and weighs aproximately 3kg. I have 2 half-kg weights ziptied to the sizes of the plate near the top on each side (so 2kg total)...I have dive right quick release/dump pockets with another kg in each, and I wear 2 kg blocks on a weight belt. (8kg total)

If I am diving in a thicker undergarment I swap the 1kg weights in each pocket for 2kg weights, the 1kg blocks are moved to the weight belt (12kg total). I find 10kg wiith my thickest undergarments too little at the end of the dive and 12kg is almost too much but as long as my trim is good I figure the slightly extra weight is worth it for the extra comfort (warmth) I get towards the end of the dive when we are shallow like at the safety stop.

One pound extra due to the valve of your pony tank is not really that significant.

-Z

 

[Divectionist]

How do you like your 3l steel? Is it the faber also? I opted for the 2l because 16cuft is plenty for my 20m dive spots and consumption rates. It's quite short so I rigged it with minimal slack for the shoulder and hip. How come you use the crotch D ring instead of the hip? Do you wrap the tail end back around your hip to the crotch D ring?

Mine without the pony:
SS backplate 5.3 lbs
SS STA 2.2 lbs
Lead 6 lbs for 5mm wetsuit+2.5mm hooded vest, of which 4 lbs live on the upper cam and 2 lbs in waist strap pockets. No weight belt.

That makes me spot on neutral at the safety spot nearing reserve pressure. I'd like to keep it to that as close as possible, hence the worry about each pound here and there. In theory, dropping 3 out of 6 lbs all on the left side should make little difference to my proper weighting and hopefully counter any rotation, with a pound or so margin in case of an empty pony at the safety stop with poor surface conditions.

 

[Zef]

The 3 liter belongs to a friend and dive buddy who has long term loaned it to me.

I like it but it took a bit to get used to the added "clutter" on my left side. I am left handed so I naturally do things with my left hand/arm and found that things like reaching for my inflator hose were initially affected by the cylinder being there. I have acclimated to it so its not a big deal at all any more.

My crotch strap has a d-ring in the front and one above my butt. I use the one above my butt....it pulls the cylinder back out of the way. I could use my left hip d-ring but it seemed like the negative cylinder would ha ng more to the front that way. I tried rigging a bungee loop off my backplate so I could unclip the bolt snap on my shoulder/chest d-ring the way some swim with stage bottles but the roll of bungee I have is 1/8th inch and not strong enough/too elastic that it did not effectively hold the bottle.

I have not weighed the 3L bottle yet. I dive in a drysuit so I am adding air for comfort/warmth and that serves double duty to maintain neutral buoyancy particularly at shallower depths. While the water temps are cold, getting perfectly neutral is kind of counter productive to being warm as one needs to account for the air they need/want in the suit for warmth and comfort towards the end of the dive when the primary cylinder is more buoyant. With a wetsuit I only 0.5kg but dive with 1.0kg split between my right and left side...there seems to be a greater fudge factor, at least for me, when diving dry as explained above there is a need for the extra weight at the end of the dive....but that is within reason as I hate being "over-weighted" for instance, I am currently using a 12L cylinder on my back, I find the 15L cylinders my club has too be heavy and cause me to be unstable. I am sure I could get used to a 15L tank but as much as I like being underwater blowing bubbles, I get kind of bored at about the 60 minute mark. I would rather do 2 dives on a smaller tank than 1 super long dive on a larger one. Both volumes are available to me all the time so I can choose based on the occasion but I rarely have a need for a 15L.

As mentioned, I have not reduced the amount of weight I carry on my left. Perhaps I will experiment with that, but I don't currently feel that I am resisting the weight of the cylinder trying to rotate me. I did need to move the weights ziptied to my plate further towards the top to balance my trim, but I don't think that was related to the pony bottle so much as the ziptied weight is something new I am playing with.

While the whole weighting issue can be done super scientific it really does not need to be in my opinion. I know that with every change to my configuration (thicker vs thinner undergarments, older vs newer wet suit for examples) the amount of lead I need changes. I log the amount of lead I am carrying along with what my configuration is and note if it is too much, too litte, or just right. Every now and then I will try to dive with less sometime it works and sometimes I need to pick a big rock off the bottom and mentally note to add lead back for the next dive with that configuration. I don't get too carried away with calculating everything to be perfect.

-Z

 

[stepfen]

If you know your "perfect" or better preferred weight without the pony, I wouldn't change it when I carry one.
Yes you will be a bit overweight under normal circumstances with the pony but there are cases you might have to abandon it (say you accidentally drop it to the abyss, donate to an aoa diver, sip the air in an emergency etc). If you are perfectly neutral with it you will end up positive at the
safety stop without it which can be more dangerous.
The way I handle this is I weight myself for the main equipment (suit, main tank, weight belt, BPW, fins). Any extras (camera, pony, stage etc ) are just that : extras that can be dropped if needed at any point. And yes I have to live with their extra weight (if any).
Just my 2c to give you some food for thought.

 

[Divectionist]

If you know your "perfect" or better preferred weight without the pony, I wouldn't change it when I carry one.
Yes you will be a bit overweight under normal circumstances with the pony but there are cases you might have to abandon it (say you accidentally drop it to the abyss, donate to an aoa diver, sip the air in an emergency etc). If you are perfectly neutral with it you will end up positive at the
safety stop without it which can be more dangerous.
The way I handle this is I weight myself for the main equipment (suit, main tank, weight belt, BPW, fins). Any extras (camera, pony, stage etc ) are just that : extras that can be dropped if needed at any point. And yes I have to live with their extra weight (if any).
Just my 2c to give you some food for thought.

It's a fair comment. I'll just sling it on top of the rest for the first try this weekend (provided my first stage arrives in time!) and see how it goes.

I may end up diving properly weighted incl. pony when going solo and diving a tad heavy when there's a chance of having to hand it off. The weight of the air in that tiny thing does not bother me.

As so often, the sweet spot may lie somewhere in the middle.