That is what happens when Fill stations have no understanding of gas laws or DOT stampings. A little training goes a long way in customer service and client retention.
Air Fill Protocol
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Try this out... It's just for fun, to see how temperature affects pressure. Yes, I did convert to kelvin 
but its for fun only!
http://db.tt/yC8as1OL
but its for fun only!http://db.tt/yC8as1OL
Spg01
Contributor
Like others have said, check the pressure before you leave the shop. If your cylinder is still warm or hot when you check it, expect the pressure to be lower when it is cool. Some people go to a higher pressure so when the cylinder is cool it is at the correct pressure. Others will not go over the rated pressure and top it off once it cools. Either way if I am shorted by 800 psi they would hear about it.
Darnold9999
Contributor
If I want the fill to be done while I wait I expect a slightly under full tank 1-300psi - if I want a full tank I leave it for a couple of hours or overnight so the shop can fill it, let it cool and then top it off. I expect it to be full in that situation if not I will complain/and or go somewhere else.
Typically the local shops around here all do this.
At 2200 I would have let the shop know and would expect them to offer a free fill as compensation. As divers they would know how annoying it would be to get a short fill and find out on the beach.
On a "fill at the dive site" kind of situation which this sounds like - put the reg on at the fill station and check the pressure. Someone doing that kind of work can easily miss topping up a tank. A liveaboard is a good example of this. Have ended up with short fills a couple of times on charters as somone got distracted in the press to fill 20 tanks in a hurry. Topping up only takes a few minutes.
Typically the local shops around here all do this.
At 2200 I would have let the shop know and would expect them to offer a free fill as compensation. As divers they would know how annoying it would be to get a short fill and find out on the beach.
On a "fill at the dive site" kind of situation which this sounds like - put the reg on at the fill station and check the pressure. Someone doing that kind of work can easily miss topping up a tank. A liveaboard is a good example of this. Have ended up with short fills a couple of times on charters as somone got distracted in the press to fill 20 tanks in a hurry. Topping up only takes a few minutes.
Just about any shop near me thinks that a 3000 PSI rated tank cannot be filled past 3000 PSI even during a fill. For the same reason one cannot every actually receive a fully rated fill -- even after a top-off.
An 80cf rated volume of a tank rated at 3000 at room temperature (72*) would acutally be about 77 CF but lets just say 80 for this argument. If that volume warms up by some degrees you may have 3200-3300 PSI but it is still the rated volume and will cool off to about 3000 PSI. Even during Hydro they fill the tank to 5/3's of the volume (meaning 166%of its rating which means a very high PSI) and if it passes hydro then the tank can handle a few hundred extra PSI during a hot fill even when that extra PSI is the same volume rating. If you have a full 3000 PSI fill and leave it in the summer heat it may expand to about 3200 PSI but it is fine -- it will cool off when you hit the water and contract back to 3000 PSI.
When I do my own fills I always overfill a tad so it cools off to its rated pressure but no shops around me will do that. Sometimes I attest it to not fully undersanding the laws/rules. Other times I attest it to insurance paranoia. Either way the only times I ever truly get a 3442 fill on my HP doubles sets is when they blend with Helium because then they compute exact PSI's for He and O2 and watch it during the top-off. But then I also have to leave my tanks with them over night. For any other fill I usually get about 3300 PSI but have yet to have that get in my way though it would if I were on 2640/3000 PSI tanks.
An 80cf rated volume of a tank rated at 3000 at room temperature (72*) would acutally be about 77 CF but lets just say 80 for this argument. If that volume warms up by some degrees you may have 3200-3300 PSI but it is still the rated volume and will cool off to about 3000 PSI. Even during Hydro they fill the tank to 5/3's of the volume (meaning 166%of its rating which means a very high PSI) and if it passes hydro then the tank can handle a few hundred extra PSI during a hot fill even when that extra PSI is the same volume rating. If you have a full 3000 PSI fill and leave it in the summer heat it may expand to about 3200 PSI but it is fine -- it will cool off when you hit the water and contract back to 3000 PSI.
When I do my own fills I always overfill a tad so it cools off to its rated pressure but no shops around me will do that. Sometimes I attest it to not fully undersanding the laws/rules. Other times I attest it to insurance paranoia. Either way the only times I ever truly get a 3442 fill on my HP doubles sets is when they blend with Helium because then they compute exact PSI's for He and O2 and watch it during the top-off. But then I also have to leave my tanks with them over night. For any other fill I usually get about 3300 PSI but have yet to have that get in my way though it would if I were on 2640/3000 PSI tanks.
dfx
Contributor
actually the burst disc/opv will (okay, "should") go first.....
Assuming a proper burst disc, I find it highly questionable that the tank will rupture at just a 200-300 PSI surplus (which will eventually cool down to the proper service pressure). I also find it highly questionable, at best, that an in-hydro cylinder will fail with just a few PSI overage, also.
So my point stands well within reason and believability. Though I'll happily concede your point, also, that given enough temperature a tank will fail. But a cylindar doesn't get that hot during a responsible hot-fill to sufficiantly warrant stopping at exactly the rated service pressure vs. +200/300 PSI on safety reasons pertaining to heat fatique alone.
Cleavitt
Contributor
It may seem odd, but he is correct and it makes sense if you really think about it. The engineers that design these cylinders and the government agencies that regulate them are certainly aware that temperature affects pressure. They design the tanks to contain pressure including common scenarios like storing the tank in the sun or in the truck of a car on a hot summer day. Then they add an additional safety factor on top of that. Therefore, these cylinders are designed to safely store pressures much higher than their "rated" pressure. If they weren't they would be blowing up everytime someone left one in the sun for too long. However, they still need to assign a pressure rating to it so people know what is considered "full" or safe for that tank. That rating is based on "room temperature" since that is the temp the tank is most likely to be most of the time. Room temp is arbitrarily defined as 72 degrees in this case. In warmer conditions (like during a fill, or nearly any time of year in Florida) it would be within the design specs to fill the tank to an equivalant pressure for that temperature. It's really no different than filling a tank very slowly to 3000 in a 72 degree room and then storing it in an 85 degree room afterwards.
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