OMS vs Pst?

[Divemstr13]

There is a substaial layer of zinc between the steel of the tank and the outer coating not to mention the epoxy coating. A while back OMS had some boots that did not drain well and that caused some water problems. That issue has been resloved. Once again the real issue is which tank is prone to rust on the inside.

Definition: Inside of tank; part of the tank that holds the air that will reach your lungs.

I dont want rust on the inside of my tank, hence I own Faber. I have done to many VIP's to ever be convinced otherwise.

 

[Lost Yooper]

Primarily because the PST 95 is more negative than the Faber (-10.4/-3.3 vs. -8.5/-1.2). I also like the galvanizing of the PST rather than the painted Faber. Paint can hide stuff. The only downside to PST is the cost, but I like 'em and think they are very much worth it. I bought the Faber for single tank diving, and I needed one fast and that's what the shop had. It makes a nice hanging O2 bottle.

Mike

 

[Iguana Don]

Originally posted by Bob
Well, rust is the major issue for the OMS tanks. Rust hides under the paint and is hard to detect. As everyone knows, if the rust isn't caught quickly, you've got a worthless tank on your hands.:tree:Bob.

As a matter of fact, I believe there was a warning or a recall from OMS on this very subject, about a year ago.

 

[The Chairman]

Your figure of 0.081 lbs/ft2 for air... I assume that this is based on STP???

 

[Rick Murchison]

Well, now, that depends on whether ye're talking about the chemist's STP or the weatherman's, doesn't it? There being a huge .00405 pound difference, don'tchaknow...
I should also clarify that I was talking about Cubic feet vice Square feet... square feet, about which you asked, inadvertantly I'm sure, of course, having no volume, have no weight.
Rick

 

[voodoogas_diver]

I realize I am a little late on this discussion, but being new to the post I thought I would give my two cents worth anyway.........

Just in case anyone cares "Standard Air" by defintion is DRY air that weighs 0.075 lbs cu/ft @ 70 deg F and 29.92 inches of mercury (or 0' asl or 14.7 psi)

 

[Divemstr13]

OMS problems where a result of a poor draining boot which was resolved.

 

[devjr]

Rick, that comment about compressors..... Virtually all of the mfgrs have been doing that. A friend of mine has a Bauer Utilus weighing 100 lbs and rated 4.2 cfm. Until then, I thought that my Stewart Warner portable was the most efficient compressor available at 80 lbs and 4.0 cfm.

Later found out I was right. The Bauer is actually rated 3.5 cfm and 4.2 scfm. the "scfm"(standard cubic feet per minute) is an industry fiction.

 

[omar]

Many standards are used to rate a compresssor, the most common being the Compressed Air & Gas Institute (CAGI) and the American Society of Mechanical Engineers (ASME) standards, which are 14.7 PSIA, 68Deg. F and 36% relative humidity.

When manufacturers list performance for compressors it is stated as "Capacity" in CFM (Cubic Feet per Minute). This is the volume of air at the inlet to the unit or Actual CFM (ACFM).

When you express your "Demand" in Standard CFM (SCFM), you are saying that you want this compressor to deliver this CFM even at your worst case conditions.

To convert SCFM to ACFM you need to determine the actual versus standard humidity, atmospheric pressure, vapor pressure, and temperature. (ie real vs. ideal)

omar

 

[devjr]

Omar, get real; the manufacturers of portable diving compressors do not care about this stuff. They have invented their own definitions. I know what SCFM means. However, the manufacturers' marketing people define it as the filling rate of an 80 cf(actually 77.7cf) tank starting at the 500 psi mark. This is similar to a golfer's handicap but in this case it is fraud. They pretend everything is on the up and up by covering their butt in the fine print. Lately, they aren't even doing that.

The difference between 4.2 cfm and 3.5 cfm is a thousand bucks.

Edited: one more thing; the only performance criterion that the buyer is normally concerned with is Free Air Delivery at standard atmospheric press and temp. This is only number that should be broadly advertised.