Good article - I never knew that the odor could fade so easily. However, it certainly is in contradiction with my experience, which is that the ethyl mercaptan odor is damn difficult to get rid of. Although my experience is generally with older tanks that probably have had continuous use.
Bob
They are probably self purging, since the vapor from the tank goes into the evaporative emission control system. I presume that would push out the air too.
I'm not an expert on any of this, just speculating. But gas tanks are vented and the gas fumes would probably displace most of the air in the gas tank, no? Also, there may be different magnitudes of potential explosive force between gasoline and propane. I know that if you shake up closed gas can, the pressure inside increases for a while at least.
The military is using a newer type of bomb now that disperses a cloud of (I think) liquidized propane and then ignites the vapor. Has a stunning blast effect IIRC.
Hey Roy,
The retail supplier of any new 20# tank here will do the required purge, and do it for free. I've never asked why it is done, but II assume that the purpose is to make sure that there is no trapped air inside to cause a problem if it is released into a burner. Lately, places like Home Depot are carrying pre-filled new tanks though.
Take care.
Brian Laws>Just what is involved with filling a new propane tank. I just bought a
Hey Lane,
And here, it's done with the tank sitting right on a special weigh scale.
Take care.
Brian Laws>> Well I can buy the reasoning behind it, but at 25 a whack is out of
Hey Clare,
That reminds me of something happened to me last year. I took a 20# in for a refill, and also one of those ones that is used in a horizontal position as fuel for a lift-truck. They are maybe two or three times the size of the 20 pounder, but are aluminum. The service depot charged me less to fill it than the 20 pounder flat fee of $ 12 Cdn, but I just assumed that maybe it wasn't empty.
Take care.
Brian Laws>>
Hey Richard,
If by "gas tanks", you mean automobiles, they are. Right on the vehicle assembly line, with special "nozzles" on the filler.
Take care.
Brian Laws>Jack Erbes writes:
No, the canisters just absorb fumes coming out of the tank. Doesn't affect what goes into the headspace. Air is definitely going in. There is even a changeover of the headspace as the ambient temperature causes the gasoline vapor pressure to go up and down and "breathe"; this is why ambient humidity can enter the tank as water vapor and condense when the temperature falls, repeating enough to cause liquid build-up, and the attendant problems in freezing weather, and the need for fuel tank dehydration with the little bottles of ethanol.
Besides, cars never had anything but simple fuel caps for many decades in the past, and there are plenty of machines (like lawn mowers, etc.) that have only that now.
Fact is, the headspace in a gasoline fuel tank is mostly air.
Gasoline vapor has more explosive energy than propane (much heavier molecules), so if anything the explosive risk is higher than propane.
All of which leads me to conclude that explosion hazard is not the primary, if any, risk mandating the purging of propane tanks.
Moisture plays a big reason for purging. As the propane evaporates into gas it gets colder. Ever see frost on the outside of a tank? Moisture inside causes ice crystals that can plug up regulators, and flame orifices etc. Can cause a big head ache.
I had this done (for free) with two new tanks (20lb) that I purchased. The guy doing stated that if the moisture is not purged from the tank, then the valve may freeze up when in use. This would kill any output from the tank.
I filled mine at a Flying J gas plaza. I have also had good luck using smaller mom/pop places like the local feed mill and a small one man used trailer business. I realize that the 100lb probably needs to be filled by a truck coming to you, but what the hey ...
I've bought several new propane tanks, they've all had to be purged. You DO NOT want air mixed with your propane in there. Purging amounted to opening up the bleed screw while propane pumping was going on, screw remained open until propane fogged out of the opening. The tanks were then filled to proper weight. I got to pay for the propane that escaped, there was no extra charge for the filling station guy having to use his screwdriver. You got ripped off. On two of the new tanks there was considerable air pressure in the tank before they were even hooked up. The last one I bled down before hauling it over to the rental place where I get tanks filled, took less time that way. It took about 15 minutes for the 60 lb tank to quit passing air after I opened up the screw, there must have been a lot of pressure in there. I suppose they use it for checking for leaks after assembly, probably roll them through a water tank after pressurizing and look for bubbles at the joints. At least being pressurized that way assured me that it wouldn't leak when filled.
You need to find another, more honest, supplier.
Stan
Well my dealer did not charge for a purge. He stated the main reason they are purged, is, even though the factory makes and pressurizes these tanks before shipping, when they are setting in storage it very common for folks to open valves etc. This allows atmospheric pressure containing moisture to get in the tank. This moisture can freeze and create a stoppage of gas flow during use. Its not to prevent an expolsion etc,. merely to keep the valve and its orifice from freezing up. He stated that other than freeze up potential its relativerly harmless, and its not going to cause any dodgeing of bullets.
He also stated they use alcohol that they pour into a tank to help remove any accumulated moisture if need be. He did not charge me to purge the tank. Pretty nice old fellow. He must know what he is talking about as he has been doing it 49 years now.
He showed me a tank that had moisture accumulated inside of it, and was allowed to set with the valve open after it was empty, and from what they figure it sat this way in a shed on its side, for many many years. On filling the tank (prior to the OPD valves and enforcement of
12 year certiify check) the tank spit down the side for about 10 inches long, looked just like a sawzall made the cut..... At 100 deg there is approximately 200# psi and at - 44 deg there is 0 pressure.Anyway now I am topped off on all my tanks and ready to make some serious moten metal starting tomorrow. I got an order for a batch of aluminum and bronze sundials and some other decorative cast items from a concrete garden statue manufacturer, have 3 wheels to cast for my bandsaw, as well as a blade guide bracket, and table pivots. Spent most of the afternoon making a few more flasks and raming up molds for tomorrow.
Thanks for all the input on my initial question on purging.
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Where I have filling done, they do both, the tank goes on a scale, the tare weight gets set, the fill weight gets set and pumping commences. When the scale comes up to balance point, the guy quits and I pay for the amount on the pump meter. I won't do business with a guy that doesn't have a scale for propane tanks and I don't do the flat fee bit, not many in this area do except for the tank exchangers like the supermarkets and home improvement joints.
Aside from safety considerations(and they're considerable), air won't liquify at propane pressures, so if there's a lot of air in there, you may not get a full bottle, or if you do, it'll be under a lot more pressure than just propane would generate. It will eventually purge out if you just draw vapor, but it is a hazard having mixed air and propane vapor being drawn out. Purging of a new bottle is just so easy to do there's no reason not to and charging for it is just about theft. If somebody tried that on me, I'd head on down the road to a different supplier.
Stan
there was a thread in rcm a couple of years back about rail and truck gas transport tanks collapsing, after being serviced or repaired. the tanks were at closed up at 1 atm, (IIRC). --Loren
Interesting, the business I go to that uses the meter only is a huge commercial outfit that fills many of the tanks you see at gas stations, rental yards, home heating tanks etc, etc. I'd sure think that they would know what they are doing. And even at the "smaller" places like rental yards that I've gone to in the past uses the hose meter system. I've never had a tank weighed.
Any chance there is a state law where you are at requiring weighing.
Lane
My understanding is that that is not a proper purging.
Per NPGA bulletin 133-a To purge a container, the following steps should be taken:
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Lane
Gasoline tanks are vented to atmosphere when they are filled - so they purge themselves.
As I stated it is LAW in Canada. We tend to have significantly higher safety standards here in Canada than you have in the states. Americans tend to get their hackles up when laws are passed forcing them to do anything that is "good for them".
>
Obviously not, if they are open to the atmosphere.
the one metro propane distributor in N.Dallas used both scale and meter to fill bbq tanks. he never looked at the meter, just took the printout and handed to the customer. although a flat rate, the office wanted that ticket.
wrt purging, only in Tejas have i been asked for payment to purge. most dealers automatically purge everytime they fill. as to repeating
5x, well i have never seen it done. maybe you guys that do pay could comment on that?...>
agreed, the dealer i asked said that the unpurged tank would have intermittant gas flow for a time, but eventually would function normally. if your bbq or pilot keeps dying on a new tank, that could be the problem. --Loren
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