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..."

 

[swall]

Rod--Amoco's "final filter" was incorporated into their TV advertising in the mid 1960's, which is why I remember it so well. But, like your Chevron experience, these types of filters were probably common among the various brands of gasoline here in the midwest. Only Amoco seems to have made a big deal out of it.

 

[rmw]

When I drove diesel vehicles I only fueled from pumps that had a filter on the pump. At least with gasoline, the vapor pressure in the tank minimizes if not prevents breathing of atmospheric air laden with moisture, but diesel has a totally different vapor pressure.

To what romke said, I have seen them stick the tanks many times when the tanker was there-they have to stick it to get the initial level and they stick it after to verify the amount delivered, and I have been shown the paste many times, but I have never seen a tanker drive off loaded if the stick showed the presence of moisture. Normally nothing more was done than to inform the station manager that his tanks needed pumping but the fuel still was dropped.

And, if you are wondering what I was doing there after what I said above about fueling when the tanker was there, when I drove diesel vehicles I fueled from the diesel pump many times when gasoline was being delivered but before I did, I made sure that there was the familiar "1203" on the Haz plackard on the tanker and not the diesel number (which I can't remember at the moment-is it 1893?

rmw

 

[evelrod]

rmw, I just posted to the gas station thread in the Pub and it reminded me of a lot of things, including "sticking" the tanks. I did that at the end of each day. I worked the evening shift and deliveries were usually in the morning so I don't know how they did it but, I suspect it was the same as I did. Just stuck the stick in the tank and recorded the amount. Never looked for water or anything else. We also recorded the readings on each pump at the beginning and end of each shift and recorded the figures, along with the money amount taken in, in the book. We generally sold about 600 gal. and always made sure that the money matched or slightly exceeded the fuel pumped <grin>. The owner was very strict about making sure customers got what they paid for. He did not mind paying low wages, though!

Swall, I remember the "Final Filter" adds. In the late 60's one of my sponsors was Union 76, so I seldom if ever shopped elsewhere unless it was an emergency. After '73 I shopped at a local ARCO that had been very kind to us during the red flag/green flag crap.

Rod

 

[robsalv]

...the vapor pressure in the tank minimizes if not prevents breathing of atmospheric air laden with moisture...

Does it prevent atmospheric ingress? I'd discounted that aspect in my thinking about possible sources of water in an underground storage tank.

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

 

[rmw]

You are dealing with two issues here. In a static state, the vapor pressure of the gasoline blankets the atmosphere above the liquid making it difficult for atmospheric air to enter the tank. Smart guys that are a whole lot more conversant about the vapor pressure of gasoline and partial pressure relationships of the gasoline vapor/air mixture will have to give the exact details. Point being, storage tanks holding gasoline have to have special vents or even floating roofs for the really big tanks, while diesel tanks for comparison don't.

This helps with the breath in/breath out of the atmosphere above the tank due to ambient temperature swings (so does the tank being buried.) Diesel tanks again for a point of comparison don't have the resistance to air ingress caused by the vapor pressure and when air enters and the moisture in it condenses on the tank walls, more air is drawn with more moisture which then condenses, etc, etc. To put it simply, storing fuels in diesel (distillate) tanks is a whole different world than storing gasoline in tanks.

However, the other condition that has to be dealt with in this discussion is the fact of air being drawn in when the tank is pumped out. No amount of vapor pressure is going to overcome that. The pumping rate at a service station is entirely different for a gasoline pump or two or three pumping simultaneously from an underground tank and the pumps designed to empty a large above ground tank in the minimal amount of time.

All in all, while moisture does get into gasoline storage tanks via the ingress of moisture laden atmospheric air, it is less of a problem than with a similarly arranged diesel storage tank.

rmw

 

[stookeyfpe]

Air enters into every underground or aboveground storage tank used for the storage of motor fuels. All underground or aboveground storage tanks are equipped with an opening called a normal vent. If the tank is used for Class I flammable liquids such as unlead gasoline or alcohols, the vent is known as a pressure-vaccum vent, which remains closed except when product is introduced into the tank (unloading by a tank vehicle) or when product is removed (via pumps on top of the tank that are piped to the dispenser). The normal vent is required by NFPA 30 and NFPA 30A as well as the International Fire Code.

For tanks storing combustible liquids, e.g., diesel fuel, the vent is open the the atmosphere.

As to "stiking the tank" with a wood gage pole, that's an old practice. Most new stations I am involved in rely on electronic tank measurement systems, as they are part of the overall liquid containment system. However, a wood gauge pole is commonly purchased to confirm the accuracy of the electronic tank measuring gage.

 

[CCycle]

In my first post I was trying to keep it simple and just answer the op. But since there seems to be interest, here is more info. This is speaking of the USA.

The electronic service station came in about 20-25 years ago when the Feds mandated tank gaging to detect leaking tanks. Oddly enough the practice of sticking the tank produced leaking tanks. The daily process of sticking the tank scrubbed off the protective oxide coating when the stick bumped the bottom of the tank. This after time made the tank leak. Later steel tanks were provided with a steel plate welded in below the opening to try to prevent this problem. But by that time the problem was massive.

Now we have fiber glass tanks with electronic gaging. The old practice of sticking a tank will not provide the accuracy required for leak detection. There are various water detectors. The time of flight, sonic method will tell you the height of fuel and water in the tank. It detects the water to fuel as well as the fuel to air/vapor interface. Computer techniques linearize the height information and report the actual gallons of fuel and water in the tank.

This information is telemetered to central control. A running inventory is maintained. The equipment is capable of detecting inventory discrepancies of as little as five gal. The information is used to schedule fuel drops, schedule service as well as detect leaks or theft. The service station attendants don't have to do or know anything. The telemetering link is also used to authorize credit cards for pay at the pump and can also keep tab on the cash register. In fact they can change price and even change the prices on the bill boards from central control.

I don't think you will find any of the old suction style dispensers in public service nowadays. It was quite a chore to change prices on the old stations. The old mechanical dispensers do not have the range to calculate fuel price with today's prices. Also on the old fuel filters, they were designed to plug if there was a slug of water.