Comparing PST 104's doubled and OMS 112's doubled. Any input would be helpful.
OMS vs Pst?
- Thread starter Divesherpa
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large_diver
Contributor
All stats are for one tank.
Physical Size:
Height and width are virtually the same
Weight on Dry Land:
PST 104 = 46 lbs.; OMS 112 = 41 lbs.
Buoyancy:
PST = -5.3 full, -2.5 empty
OMS = -8.0 full, -1.0 empty
Exterior Protection:
PST = hot dipped galvanizing process
OMS = some sort of spray galvanizing process
Hard to say which is better -- most opinions I've heard favor the PST process for better rust resistance. I have heard at least a few folks say they think the OMS tanks are more durable.....
See link below for tank stats. Hope this helps.
http://diverlink.com/gear/tanks.htm
Physical Size:
Height and width are virtually the same
Weight on Dry Land:
PST 104 = 46 lbs.; OMS 112 = 41 lbs.
Buoyancy:
PST = -5.3 full, -2.5 empty
OMS = -8.0 full, -1.0 empty
Exterior Protection:
PST = hot dipped galvanizing process
OMS = some sort of spray galvanizing process
Hard to say which is better -- most opinions I've heard favor the PST process for better rust resistance. I have heard at least a few folks say they think the OMS tanks are more durable.....
See link below for tank stats. Hope this helps.
http://diverlink.com/gear/tanks.htm
Someone's math is a bit off.
If the PST 104 is negative 2.5 lb empty, then it's negative 11 full. Unless they mean 500 psi as empty, then it'd be negative 9.5 full.
Rick
If the PST 104 is negative 2.5 lb empty, then it's negative 11 full. Unless they mean 500 psi as empty, then it'd be negative 9.5 full.
Rick
large_diver
Contributor
And here is a different (but similar) answer from a "DIR" dive shop in WA
http://www.fifthd.com/gear/tankspecs.html
They maintain that the PST LP104s are -4 and -1 (full/empty)
Rick -- tell me more about your calcs.
http://www.fifthd.com/gear/tankspecs.html
They maintain that the PST LP104s are -4 and -1 (full/empty)
Rick -- tell me more about your calcs.
This information came from http://www.huronscuba.com/
PST 104 0.7 empty w/valve -8.2 full w/valve
OMS 112 -1.0 empty w/valve -8.0 full w/valve
:tree:Bob
PST 104 0.7 empty w/valve -8.2 full w/valve
OMS 112 -1.0 empty w/valve -8.0 full w/valve
:tree:Bob
Air weighs .081 pounds per cubic foot (104 CF weighs about 8.5 pounds). When you put it in a tank, the tank's weight increases by the weight of the air you put in it. The only way you can have the buoyancy change less than the weight of the air you put in the tank is to have the tank expand to displace more water, and expanding to displace another 5.5 pounds (all but 3 of the 8.5 pounds that 104 CF of air weighs) is a bit much, don't you think? (For those of you who think of tank sizes in liters, for the figures given to be accurate, the tank would have to expand by two liters when you fill it - I don't think so)
Rick
Rick
large_diver
Contributor
Rick -- OK -- that makes sense to me.
What makes less sense to me is that the delta between the full/empty stats for the larger OMS tank (7 lbs) is less than that for the PST (8.9lbs).......hmmmm. What other variable is affecting this?
What makes less sense to me is that the delta between the full/empty stats for the larger OMS tank (7 lbs) is less than that for the PST (8.9lbs).......hmmmm. What other variable is affecting this?
I suspect it's a difference in the definition of "empty." To many, that means 500 psi, while to others (me, for example) empty means empty.
In the case of a LP 112, for example, 500 psi leaves 21 CF in the tank, so the difference between "empty" and full is 91 CF, which weighs just a bit over 7 pounds - and that makes the numbers make sense.
Scuba is absolutely *filled* with "information" like this, and occasionally that info gets repeated so much it becomes common knowledge and "well known fact." Folks don't question it because they see it in print.
It's how one heavily advertised small compressor manufacturer manages to claim a 4.2 sCFM rating for their 3.5 sCFM compressor that's *really* a 3.4 sCFM... IOW they're claiming an air delivery rate that's over 20% above reality. They've been running the same add for years, and I have yet to see any dive publication take them to task for it.
Rick
In the case of a LP 112, for example, 500 psi leaves 21 CF in the tank, so the difference between "empty" and full is 91 CF, which weighs just a bit over 7 pounds - and that makes the numbers make sense.
Scuba is absolutely *filled* with "information" like this, and occasionally that info gets repeated so much it becomes common knowledge and "well known fact." Folks don't question it because they see it in print.
It's how one heavily advertised small compressor manufacturer manages to claim a 4.2 sCFM rating for their 3.5 sCFM compressor that's *really* a 3.4 sCFM... IOW they're claiming an air delivery rate that's over 20% above reality. They've been running the same add for years, and I have yet to see any dive publication take them to task for it.
Rick
Divemstr13
Guest
OMS tanks are actually made by Faber.
That is correct.
Rick
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