Tips on Pumping Petrol

[william777]

I read this somewhere and I thought it might be of interest to some people here:

"I don't know what you guys are paying for petrol.... but here in Perth, WA we are paying up to $1.30 to $1.50 per litre.

My line of work is in petroleum for about 31 years now, so here are some tricks to get more of your money's worth for every litre:

Here at the BP where I work in Perth, we deliver about 4 million litres in a 24-hour period.

One day is diesel, the next day is jet fuel, and Petrol, regular and premium grades. We have 34-storage tanks here with a total capacity of 16,800,000 litres.

Only buy or fill up your car or truck in the early morning when the ground temperature is still cold. Remember that all service stations have their storage tanks buried below ground. The colder the ground the more dense the petrol. When it gets warmer, petrol expands so buying in the afternoon or in the evening....your litre is not exactly a litre. In the petroleum business, the specific gravity and the temperature of the petrol, diesel and jet fuel, ethanol and other petroleum products play an important role.

A 1-degree rise in temperature is a big deal for this business. But the service stations do not have temperature compensation at the pumps. When you're filling up do not squeeze the trigger of the nozzle to a fast mode. If you look, you will see that the trigger has three stages: low, middle, and high. You should be pumping on low mode, thereby minimizing the vapours that are created while you are pumping. All hoses at the pump have a vapour return. If you are pumping on the fast rate, some of the liquid that goes to your tank becomes vapour. Those vapours are being sucked up and back into the underground storage tank, so you're getting less worth for your money.

One of the most important tips is to fill up when your petrol tank is HALF FULL. The reason for this is the more petrol you have in your tank the less air occupying its empty space. Petrol evaporates faster than you can imagine. Petrol storage tanks have an internal floating roof. This roof serves as zero clearance between the petrol and the atmosphere, so it minimizes the evaporation.

Unlike service stations, here where I work, every truck that we load is temperature compensated so that every litre is actually the exact amount.

Another reminder, if there is a petrol truck pumping into the storage tanks when you stop to buy petrol, DO NOT fill up. Most

likely the petrol is being stirred up as the petrol is being delivered, and you might pick up some of the dirt that normally settles

on the bottom."

[Dixon]

be interesting if someone could whip a DIY floating roof for ya car's fuel cell haha

thanks for sharing, my regular fuel pump is slow enough as it is on high speed let alone low..but im still gunna try it xD

[byw]

Thanks for posting up these tips. Has anybody done any tests to determine what the savings/wastages are in terms of the amount of petrol per trip to the petrol station if we followed all the rules vs. breaking all the rules?

The amount of savings will determine whether its worth the hassle of getting petrol early in the morning and always fill up when the tank is half empty etc.

Cheers.

[Hiro]

Sigh, not this crap again....

I read this somewhere and I thought it might be of interest to some people here:

Only buy or fill up your car or truck in the early morning when the ground temperature is still cold. Remember that all service stations have their storage tanks buried below ground. The colder the ground the more dense the petrol. When it gets warmer, petrol expands so buying in the afternoon or in the evening....your litre is not exactly a litre. In the petroleum business, the specific gravity and the temperature of the petrol, diesel and jet fuel, ethanol and other petroleum products play an important role.

A 1-degree rise in temperature is a big deal for this business. But the service stations do not have temperature compensation at the pumps. When you're filling up do not squeeze the trigger of the nozzle to a fast mode. If you look, you will see that the trigger has three stages: low, middle, and high. You should be pumping on low mode, thereby minimizing the vapours that are created while you are pumping. All hoses at the pump have a vapour return. If you are pumping on the fast rate, some of the liquid that goes to your tank becomes vapour. Those vapours are being sucked up and back into the underground storage tank, so you're getting less worth for your money.

BS. Petrol tanks are buried underground precisely for the reason of keeping their temperature constant. Ground temperaure will vary by only a few degrees over the course of an entire YEAR, let alone day/night or winter/summer (this is the entire principle behind ground source heat pumps for year-round reverse cycle air-con - the ground is warmer than the air in winter and colder than the air in summer). And the difference between the specific gravity of petrol at 10 degrees C (an approximate ground temperature) compared to 25 degrees C (air temperature) is in the order of 1-2% - ie over for a 100L tank you might get 1-2L less. Remember the density of liquids is MUCH less sensitive to temperature compared to gasses. Also, I've read that most pumps these days compensate for changes in density - ie they dispense mass flow, not volume.

And I have yet to come across a bowser with "high, medium and low" triggers. If I just squeeze the trigger slightly it will trickle in, any more than that and it is basically constant flow (the speed is determined more by the shape of your tank and filler neck - for instance on the same bowser pump the AE102 fills much faster than the JZZ30 because the Corolla tank is under the back-seat whereas the Soarer tank is behind the seats in front of the boot. As for the fuel churning into vapours and getting sucked back out, once again you are only talking about a fraction of a percent in the short period of time that you are filling the tank. If you stand there and let the fuel trickle in you mightn't be churning the fuel up as much, but at the same time you are spending much longer filling the tank and thus allowing the fuel IN the tank more time to flash to vapour and get sucked out.

One of the most important tips is to fill up when your petrol tank is HALF FULL. The reason for this is the more petrol you have in your tank the less air occupying its empty space. Petrol evaporates faster than you can imagine.

Doesn't matter, since properly functioning car petrol systems are one-way sealed. The petrol cap can let air in to accomodate for consumed petrol, but cannot let vapour out. If excessive vapour builds up in the tank then it is syphoned off and condensed in the charcoal canister and then burnt under vacuum. It does not escape back out to the atmosphere as this is an emissions violation and has been this way for probably 30 years. Improperly operating fuel caps or charcoal canisters (ie ones that aren't serviced properly) can however affect this.

Another reminder, if there is a petrol truck pumping into the storage tanks when you stop to buy petrol, DO NOT fill up. Most

likely the petrol is being stirred up as the petrol is being delivered, and you might pick up some of the dirt that normally settles

on the bottom."

So you're telling me that they don't have filters on the bowsers? Even if they didn't, you still have a fuel filter or two in your car, so even if you did suck up a little sediment you're not going to grenade or engine (and it'd have to be a fair bit of sediment to clog up the fuel filter to. Or are you saying that the volume of sediment will mean you get less petrol :P

In short, you will save significantly more money by just filling up when the price is cheapest and driving more conservatively than ANY of these so-called "tips".

[Steven]

Most of the above rebuttal is true. The fuel industry is under incredible scrutiny these days and as such all fuel pumps need to comply with a multitude of legislation and design rules which take into account all the above.

As for crap in the bottom of the tank, all the pumps use a special hi-flowing filter system to prevent dispensing any sediment - this also goes back to ensuring the the bowser matches was it dispenses into your tank.

I could provide many tips for how to pump petrol, but most of these tips are towards what not to do so you don't annoy the guy/gal who's authorising your pump, else they screw around with you for being so stupid. Any virtually nothing to ensure you get the most out of what you pay aside from filling up on the cheapest day.