Single Tank Backplates

[Kaos]

PST LP 104 are around -12.5 lbs bouyant when full (not -54) and around -5.0 bouyant when empty. So a pair of them are going to require 25 lbs of lift at the surface when full. The plate and STA are pretty much a wash as they displace relatively little water. So at this point you are at about 33 lbs of lift.
QUOTE]

Yeah it's true, I forgot about that part... so it seems that the Oxycheq 45 would do a great job. I will obviously need to buy a doubles wing when the time comes to that next Summer

Thanks, much appreciated

 

[cool_hardware52]

One question for my own edification, what is the reduction in diameter of an aluminum 80 CF tank fully filled at 3000 psi from surface to 66 FSW?

I don't have specific info on diameter reduction due to changing from 1 ata to 3 ata on a 3000psi tank, but I'd guess it to be fairly small. (14.7 outside/3000 inside vs 44 outside /3000 inside)

A much greater relative change results from reducing the tank pressure from 3000 psi to 500 psi.

The max change occurs of course mid cylinder where it is not constrained by the top or bottom of the tank. This is also right where the cam straps are typically applied.

If IRRC the change in circumference is ~ .25"

I'll get the "PI" tape out at my next opportunity.



Regards,


Tobin

 

[Charlie99]

IIRC, hydrostatic tests include both a maximum amount of volume expansion at test pressure, as well as the maximum amount of difference between starting and ending volume at low pressure after exposure to test pressure. They were really small amounts. Does anybody have those numbers for an AL80 and a PST LP104 handy?

1/4" change in circumference sounds like way too much.

 

[cool_hardware52]

IIRC, hydrostatic tests include both a maximum amount to expansion at test pressure, as well as the maximum amount of difference between starting and ending volume at low pressure after exposure to test pressure. They were really small amounts. Does anybody have those numbers for an AL80 and a PST LP104 handy?

1/4" change in circumference sounds like way too much.

Charlie, You maybe right as I am relying on feable gray matter only at this point. Remember however that a .25" change on circumference requires only a change of ~.08" on diameter. This would be a ~ 3% change on a typical 8" AL80, on circumference.

Now you peaked my interest.



Regards,



Tobin

 

[jonnythan]

Just MO, but I added a single tank adapter to my no-STA required Pioneer specifically to move the tank away from my back a little bit. This allowed me to position the tank further up without it interfering with my head. It's much easier for me to reach the valve this way, and my trim is better because of it.

 

[Charlie99]

Charlie, You maybe right as I am relying on feable gray matter only at this point. Remember however that a .25" change on circumference requires only a change of ~.08" on diameter. This would be a ~ 3% change on a typical 8" AL80, on circumference.

Now you peaked my interest.

I briefly looked into this a few years ago when looking at tank spec's and seeing unexpected numbers for the difference between full and empty buoyancy. I figured that the difference between those two number should simply be the weight of the air, but the numbers in tables were all over the map.

My next guess was that the strange full-to-empty buoyancy change numbers were due to tank expansion, but that didn't seem to be the cause if I understand the hydrostatic test specs correctly.

 

[Dan Gibson]

I found that by using a DIN instead of Yoke I accomplished the same thing with my single tank rig.

Just MO, but I added a single tank adapter to my no-STA required Pioneer specifically to move the tank away from my back a little bit. This allowed me to position the tank further up without it interfering with my head. It's much easier for me to reach the valve this way, and my trim is better because of it.

 

[Dan Gibson]

The main reason I don't use the bolts is that early on Halcyon always sent a mixed batch of bolts. One would be long enough and the other was too short. I got tired of setting up rigs at the shop with the crappy bolts and just stop using them.

You are correct that I didn't mention fastening the wing to the plate in my first post and as Dan pointed out one doesn't need to use the bolts.

Personally however I find it better to have the wing secured to the plate...

 

[cool_hardware52]

I found that by using a DIN instead of Yoke I accomplished the same thing with my single tank rig.

I agree here. Reg type, valve type make a difference. Take a din reg add a yoke adapter, position "correctly" = bump on head.

Use din reg in angled din valve and you can't hit it if you try.


Tobin

 

[cool_hardware52]

The main reason I don't use the bolts is that early on Halcyon always sent a mixed batch of bolts. One would be long enough and the other was too short. I got tired of setting up rigs at the shop with the crappy bolts and just stop using them.

I agree here too. Once the tank is secure the wing can't leave or move. Can be a little more difficult to change tanks as you may "chase" the wing around a little, but no big deal. Nice when it comes time to break it down and clean it.


Tobin