How does a service station pump, pump!

[robsalv]

Was just in discussion with a colleague and talking about service station underground storage tanks and how water might form in the tank following the displacement of fuel and the ingress of air through the breather.

Air carries moisture, moisture condenses on the U/G tank walls, water trickles down and forms a layer of at the bottom. This is on top of any water that might come in the fuel from the delivery truck.


If service stations draw off the bottom of their storage tanks, then any sediment will be drawn up along with the water as well.

So how do service stations stop that muck being pumped into our fuel tanks? Is it purely a filtering thing, or do they draw off at some point above the bottom?


So far my searches haven't turned up anything firm on the topic.


Also, what sort of pump is typically used to get fuel from the tank to the bowsers?



The topic has piqued my curiousity.



Thanks in advance

Rob

- - - - - - - - - - - - - - -
"Life! No one get's out of it alive."
"The trick is to grow up without growing old..."

 

[carnage1]

You seem to think they do prevent that stuff from getting in our tanks. As I recall my mother ruined a brand new truck shortly after the st. hellens eruption because she got gas in eastern oregon and there was volcanic ash in the fuel that ruined the motor before the tank was even empty. I have also fixed a few cars that had intermittent problems by dumping the fuel tank and I am amazed at what you find in them. Also how much isoheat do you think would sell if we weren't occasionally getting a bit of water in our gas?
I am very curios about how the stations are set up as well, hopefully we can get some people who know.

 

[patprimmer]

AS i understand it, he tank pick up is a foot or so above the bottom so water etc collects and settles below the are affected.

I would think it would be good practice to insert a deeper tube every so often and pump the water etc from the bottom.

I am sure that not all service station operators abide b good practice.

Regards

eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[CCycle]

Service stations have all switched to submerged pumps. This is similar to cars that have a electrically driven pump in the tank. One pump will serve several dispensers. The submerged pump is a centrifugal pump that runs all the time whether people are filling up or not. It maintains a constant pressure. On larger stations there may be a second pump that comes on when the pressure drops during high demand. There is one pump for each grade of fuel. The inlet to the pump is typically some sixteen inches off the bottom of the tank. The tanks are typically 10,000 gal.

The service people periodically "stick" the tank. This means they drop a marked stick in the tank. They have what they call "water tape" which is a cream colored putty or tape they put on the bottom foot or so of the stick. This turns red if it contacts water. By this they can tell if there is water in the tank and if so how much water is there. When the water builds up to a few inches they get a pump on it and draw the water out.

The water in fuel situation changed abruptly when alcohol became part of fuel. Now the alcohol picks up the water and carries it along with the fuel. We still have the water problem with diesel.

 

[thruthefence]

I think all the underground tanks in service these days have electronic monitors, mandated by the Guv'ment. They measure ( very accurately ) free water, volume, leakage, product added, and pumped out. You still see them "stick" the tanks, though. The tanks have a small pipe, separate from the supply system that goes to the lowest point in the tank, which is supposed to be installed at a slight angle to prevent scattered slugs of water from forming. When water is observed, a small hand pump is used to remove the free water.The version we have at the airport can ( I'm told ) be programed to 'phone home' through a modem if something is amiss; leaks, 'after hours' unauthorized fuel being pumped, etc. As well as keeping the Airport Authority advised on our fuel usage, which we are charged a "self-fueling" fee per gal.

 

[patprimmer]

thruthefence

Which particular Guv'ment do you refer to or are you implying all guv'mnts world wide have this kind of regulation.

Regards

eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[evelrod]

In one of my 'less than lucid' moments just prior to retirement, I fancied the idea of buying a local Texaco station that was on the block. Lost out in the bidding to an Indian couple with $$$$$$$$$$$$$$$$$$$$$$$!!!
Good thing, too. After I did a bunch of research and found out way too much, I really wanted out. Got lucky!
Anyway, the existing tanks were leaking, etc. Replacements were two at 10,000 gal and one at 15,000 gal. I saw the pickups and they appeared to be one or two feet off the bottom, no submerged pump, several vents, etc. Fiberglass construction. Two pumps installed (that I saw, assuming a third?) located in an underground vault that pumped premium and regular (mid grade was a blend of the two ?) to the dispensing "pumps". The other 10,000 gal tank was for diesel, it was new as when I was looking to buy the station as Texaco brand it did not have diesel. New brand was initially Ultramar and now is an independent of some sort. This was in 96/97 and the station has since undergone major renovation and update. I have no idea what they have now (the tanks were replaced, again, along with a bunch of piping at the "pumps" a few years ago). I still have my motor home smogged there and buy my diesel there, too. Sure glad I did not get saddled with that project, whew!

Rod

 

[robsalv]

Thanks guys.

The question came from Australia, where alcohol blended fuels are in the minority. I hadn't even considered the impact of alcohol which should keep free water disbursed in the fuel... hopefully you folk aren't experiencing increased corrosion rates in your fuel systems.


I'm not sure about the constant pressure arrangement - well, at least in Australia. When I pick up the hose and the attendent "turns on" the bowser, I hear a pump fire up - so clearly there's a mechanical component in the guts of the bowser. Not sure just how this local pump works in regards to the larger storage tank draw off.


Anyway, the indications are that the fuel pick up is inside the storage tank at some submerged level above the bottom. Hopefully that limits the muck that gets into our tanks.


I guess it pays to avoid filling up when you see a supply tanker in the forecourt... the delivery process is sure to stir up the muck in the storage tanks for a while.


Anyway, thanks fellers.

Cheers

Rob


- - - - - - - - - - - - - - -
"Life! No one get's out of it alive."
"The trick is to grow up without growing old..."

 

[thruthefence]

The Guv'ment I was referring to, is the good old USA, or more specifically, the EPA; our 'environmental protection agency'. Back in the '90's, we had a "drop dead" date, requiring all underground tanks to meet certain criteria, leak monitoring being one of the requirements. Many "ma & pop" operations ( read: 'NOT COMPANY OWNED') simply quit the business, the expenses being too great to comply with the new rules.

 

[patprimmer]

As we now know the OP was about the land of Oz, the good ol USA's rules and regulations are hardly relevant.

Regards

eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[FJTOM]

When in the mood to buy gas, always make sure that the tanker truck is not filling the storage tanks. Filling stirs up the sediment/water and could plug your filters quickly. Happens to many. Don't buy gas when the tanker truck is there!

 

[thruthefence]

Sadly, We seem to be getting more & more "irrelevant" with each passing day.

 

[patprimmer]

In the words of our most famous bushranger Ned Kelly as he was about to be hanged "such is life".

Regards

eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[carnage1]

Yes we are experiencing increased corrosion in our fuel systems, as well as the inability to store gasoline due to how quickly it degrades with all the junk in it. In our family's 1910 Michigan we are now running avgas as the stuff from the pump smells bad and degrades quickly in a non sealed tank. It also seems to ruin the cork seals fairly quickly to run the state mandated 10% ethanol.

 

[evelrod]

Interesting. I've not experienced any problems in my newer cars, but in my '30 Ford, after 75 years with no problems, the fuel gauge float (made of cork) simply melted. Hmmm. I replaced it with a plastic float replacement and since the rest of the fuel system has no rubber (all steel) I guess I'm safe. Bummer.

Rod

 

[swall]

I heard that the tanker truck phobia was myth.

 

[rmw]

The tanker truck phobia is not a myth. Think about it. The tank has a low level of fuel. Water and accumulated muck is hugging the bottom of the tank (yes, less water now that the alcohol aids in its dispersion, but still the airborne dust and mold and etc mentioned in the OP is still there,) all calmly resting in the bottom of the tank disturbing no one and then the tanker drives up and within a matter of just a few minutes drops 9500 gallons of fuel (or some major portion thereof) into the tank. What do you think all that muck is going to do, remain calm?

If you have ever been at a station when they 'sticked' their tanks and looked at what is on the stick (not necessarily in all tanks-some do take care of their tanks) brings up, you'd be a believer.

I just underwent a round of repairs, filter changes, one injector and a lot of aggrivation after stopping and filling up at a brand name station while traveling out of state. The car ran fine for two days prior to this fill up and the week after was some kind of heck. Just a coincidence, I'll never know. But I did have my mechanic drain the inlet side of the filter into a clear glass container and show it to me. It was gasoline, but it looked like the Mississippi river to me. What a mess.

And, BTW, there was no tanker in sight-had it just driven off? I don't know. And how do you know not to fill up then?

But myth, no, not hardly.

rmw

 

[romke]

the practice of maintaining the tanks may vary from country to country. basically though fuel suppliers follow the same rules: underground tanks are tilted a few degrees so water and sediment run to the lowest part of the tank and accumulate there. before a tanker fills up a tank a check is made with a stick to see whether there is water present. the check is made by covering the end of the stick with a paste that changes its color when in contact with water. if water is present, the tanker normally is not supposed to unload before the water and sediment have been pumped out and the tank inspected for leaks.

the fuel delivered is normally without water, when filling an underground tank some of the water and sediment may indeed be stirred up. when you see a tanker unloading, it is therefore a good idea postponing filling up for say 15 minutes. the fuel is sucked out from the tank at the "high end" of the tank and usually about 10 cm above the bottom.

occasionally incidents may happen. the most common causes are leaking tanks, so water from the surrounding soil may enter or very heavy rainfall that floods the above ground area for a while and by doing so also manages to get into the storage tank. tanks should/have to be inspected at regular intervals, and in more "wild areas" with less regulation this might be overlooked.

major oil companies are quite aware of the necessity of good housekeeping, some independent gas station operators might not always be that attentive.

the use of alcohol substances have aggrevated the problem since it readily takes up some water and that may lead to corrosion problems and to problems with floats and gaskets etc in older vehicles. experience in for example brazil has shown that those problems can be avoided with good housekeeping and the use of alcohol compatible materials.

water in diesel fuel can also lead to problems. apart from the obvious problems with injection pumps, water may stimulate the growth of certain bacteria at the water/diesel interface which occasionally lead to frequent filter blocking. the growth of bacteria can be controlled by adding a suitable "bacteriakiller" to the fuel. this is not done on a permanent basis, since bacteria tend to get resistent to them. therefore they are only used when necessary and the types used are frequently changed to avoid resistency.

when problems occur, usually quite a large number of vehicles is involved. an unnatural number of complaints within a relatively short time (say a couple of hours) usually triggers action: the gasstation is temporarily closed and a thorough inspection is carried out and eventually repairs are made. if you still happen to have a receipt from the fuel you bought, reapirs necessary for your vehicle are usually paid for by the insurance the gasstation has.

this however is the situation in "heavily civil and regulated" europe, in other parts of the world things might be a little different.

 

[swall]

I guess I can't argue with the engineering logic about fluid flow from the tanker disturbing the sediment in the tank. Makes me long for the days of AMOCO's "final filter"-- a cartride filter just ahead of the dispensing nozzle.

 

[evelrod]

Swall, even in 1958 when I managed a Chevron station, our pumps had a screw on filter at the out side of each pump (in those days each 'pump' really had an electrically operated belt driven pump at each station, no centrally located master pump). All I remember is changing them every so often and they were white oil filter looking things ;oD

Rod