Why is the 3000 PSI Fill Standard at Most Dive Destinations?

I have been to many dive travel locations in the Pacific and the Caribbean and it seems that 3000 PSI is pretty much standard. Recently, I have run across California based dive boats that do 3500 PSI fills.

My intuitive assumption is that the dive operators in "vacation" locations prefer to restrict the dive times and try to do this by short-filling to only 3000 PSI. Am I off base here?

80 cubic foot aluminum tanks are relatively inexpensive, and are rated to 3000 psi. And they are decent tanks at least relative to what was available before them. So I image that is the primary reason.

Also the cost of the compressor system may be an issue. I am not an expert here, but you may be able to to get to 3000 psi with a relatively inexpensive two stage compressor. To get above that you would need a three stage compressor or a booster which would be significantly more expensive in up front costs.

It seems to me that 100 cu ft or larger tanks can be rented, but you do have look around.

You know, we have these little globular tanks at work, that they compress with helium to 35000 PSI. They're about the size of a softball. If we pressurized them to, say, 20,000 PSI air, I bet two of them would give us loads of diving time.

Granted, if one fails, we probably won't have time to feel it (it'd likely be similar to having a big grenade explode next to the body), and darned few places would have a compressor set-up capable of those pressures, but what the hey.

Seriously, though; I suspect Mr. Charcharodon is on the right track. Just as energy required to accelerate increases logarithmically as speed increases, so also I suspect the energy requirements to take a tank from 3000 up to 3500 PSI is significantly higher than it was to go from 2500 to 3000. The equipment to handle those pressures is going to be more expensive to both buy and operate, and for many places, it's probably not worth the minor increase in revenues it might bring.

As Mr Carcharodon said, there are maximum safe limits for the Tank and in addition there are also limits for your Regulator, so especially when renting in dive locations, they will do the fill to the lowest common denominator, since over filling for the tank or Reg could open them up to a huge liability if it were to be the cause of an accident.

Especially when, they can't guarantee exactly what equipment is going to be used with their tanks, unless they *try* and stop people using their own gear.

So, for example, I have DIN regs that can take up to 300 bar; however, if I have to use the Yoke adapter, then I can only go to 232 Bar pressure (don't know what the lb equivalents would be).

If they filled the tanks to 300 bar (assuming they paid extra for the tanks that allow that sort of pressure fill) and I came along and had to use my yoke adapter, then they have just given me a tank that is filled higher than the maximum certified pressure of my reg under that set up.

Travel locations don't need to restrict dive time with tank pressure, they can easily set a time limit to the dives and tell you this will be enforced, if you agree to dive with the operator and break those rules, they have the right to stop you diving with them for no refund....

Aluminium tanks (which i hate) are only rated to about 207 bar which is 3000psi. Not everywhere is civilised and uses 232 steels.

There's also the fact lots of resorts fill tanks quickly and dont have water cooling so you get a hot fill that then drops pressure as it cools.

think too of the chamber rides being cut out.....

3000 psi is the authorized working pressure of most aluminum 80 scuba tanks. If you fill a tank rapidly (like is common on a dive boat between dives) they get hot. If you hot fill an AL80 to 3400 psi, when it cools it will be about 3000 +-, especially when juming into the cooler waters off California.

Most Aluminum tanks are rated to a fill pressure of 3000 psi or 210 bar! Luxfer now make a tank called an 80 / 95 which means that if filled to 3000 psi it holds 80 cu ft air, if filled to 3500 psi then it holds 95 cu / ft of air!
To fill these tanks to 3500 psi would mean that the air fill opperator would have to re set his pressure relief valve from the standard 3000 psi to 3500 psi which most opperators would not do unless he was filling most tanks to 3500 psi!
Equipment pressure would also be an issue in some cases but I think that it is because 3000psi is the norm rather than the exception!

I agree that it has more to do with the wide spread use of tanks with a 3000 psi service pressure.

As a general information cleanup.

Filling a 3000 psi tank to 3200-3300 psi when it is warm is not an overfill at all as long as it is not over 3000 psi when it cools to 70 degrees F. So in effect, when filling a tank on a boat, the fill operator does not have to stop at 3000 psi. A good one will feel the tank shoulder and then overfill by an amount that gets the tank very very close to 3000 psi when it cools. In fact someone used to sell a stick on thermometer calibrated with the fill pressure needed to get a full 3000 psi fill on a warm tank.

A "Bar" is 14.5 psi so and 232 bar is 3364 psi. Din K valves intended for yoke or DIN use are used on 3442 psi tanks and 3442 psi is 237 Bar. So in effect, as long as the yoke is well designed and intended for 232 bar/3300 psi service pressures, it is not going to spontaneously detonate at 3442 psi pressures. Most heavy duty yokes with a 9/16" yoke screw will probably handle 4000 psi with no issues and most are probably engineered for a 150% safety margin (ie: 4500 psi).

Regs are a different matter but most modern regs will not break a sweat operating at 3500 psi and many are designed for 300 bar/4350 psi service.

Most compressors that can struggle up to 3000 psi can usually make 3400 psi.

I would expect that the diving industry has settled on the AL80 because it is most economical to produce, holds sufficient air for most recreational diving purposes, etc. There are other places on Earth where the population hasn't come up to date yet and still use steel tanks and drive on the wrong side of the road, like Britain, but that is rare. AL80's seem to suit the rest of the world just fine and will remain to do so probably forever.