How accurate are servo pumps?

so with the expansion of fuel because of heat would that then mean if a road train loaded in adelaide by the time he arrived in say alice springs the truck will have a significantly larger volume on board to sell to the fuel station.who makes the profit

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Originally Posted by p38arover

BUt it's going in as a liquid, not a gas. The shut off is a float valve, not a pressure valve. (I know 'cos I've pulled them out. If you adjust the float you can get more LPG in. Seriously, I was once told that by an LPG fitter. I haven't done it.)

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My FIL was Kleenheat gas depot manager and knows heaps about this stuff. You can adjust the float, though this changes the setup, causes venting due to expansion of lpg when in the car tank and is illegal. While it is liquid, temp still plays a big part with lpg as it expands and contracts a lot more than most other liquids.
I have had 4 cars with lpg now and they all varied on filling amounts depending on ambient temperature. Its also not advisable to fill an lpg tank right up on a scorcher of a day although a bit safer than a petrol vehicle as lpg systems have vent devices and it vents as a gas not a liquid. Unfortuanately as most tanks are in the back of a car they vent inside the car and can be dangerous if an ignition source is present. I changed the vent / purge valve to a hose set up and ran it outside the car away from the exhaust.
Cheers
Craig

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Originally Posted by lewy

so with the expansion of fuel because of heat would that then mean if a road train loaded in adelaide by the time he arrived in say alice springs the truck will have a significantly larger volume on board to sell to the fuel station.who makes the profit

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Fuel delivery like this works on SG (specific gravity) not just volume. It also is calculated when filled at a certain temp / volume.

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Originally Posted by CraigE

Unfortuanately as most tanks are in the back of a car they vent inside the car and can be dangerous if an ignition source is present. I changed the vent / purge valve to a hose set up and ran it outside the car away from the exhaust.

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In theory, they are vented to the outside world by a tube which also carries the wiring, fill, and supply lines. They should never vent inside.

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Originally Posted by p38arover

In theory, they are vented to the outside world by a tube which also carries the wiring, fill, and supply lines. They should never vent inside.

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That is how mine is set up. Which is one of the reasons there is a sticker on the sealed cover saying that the cover should be in place at all times or something like that. Also why the black tubing is much larger than it needs to be if it was only to route the wiring and pipes I imagine.

I read a funny story years ago where a guy borrowed a mates charger and stopped at a servo to fill it back up with lpg before returning it, he stood there for ages waiting for the afl to shut off the pump . Well after filling with more lpg than he thought possible he decided to stop and only after smelling a strong gas smell realised that all the gas had escaped. Turned out that the owner removed the lpg tank to have it re tested or something and he was just filling the boot with lpg !

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Originally Posted by CraigE

While it is liquid, temp still plays a big part with lpg as it expands and contracts a lot more than most other liquids.

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I would have expected fuel delivery pumps to have temperature volume compensators.

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Originally Posted by p38arover

I would have expected fuel delivery pumps to have temperature volume compensators.

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And I believe they do of sorts, but when cold and I am talking 0 deg c or below you can fit more into a tank. A lot of it will be to do with the temp extremes in the area. In Kal / Kambalda we could have -2 deg c overnight at 0400-0430 when I would fill up on the way to work and get to mid to high 20s. I got caught a couple of times coming out to smell gas venting. So learnt not to fill it right up unless I was driving into Kal for work 50kms as oppossed to 2kms from servo when in Kambalda roster on (where I lived).
It not a huge amount but on cold mornings I could always get more lpg in the tanks. Great when heading to Perth or something.
As for the vents you are right they are supposed to have a vent tube, but I have seen many without them, bought a car that did not have one and most are damaged or blocked. They are generally cheap tubing that does not last and deteriorates and damages easy. I replaced mine with better quality fuel grade hose and a filter so they could not get blocked.

I had exactly the same problem with a servo on the freeway from Geelong to Melbourne. Melbourne bound side. I filled up and the tank took several litres more than anytime I had previously filled it on empty. I do track my litres per k's travelled. Stopped using them. By the way my 93 Disco Tdi on diesel seems to have a 60 litre tank as I never get more than that in it.

FYI the states had a scandal a few years ago whereby the servo's had a chip installed that gave exactly 10 litres when that was selected however gave short filling on random fill ups. Not a co-incidence was that weights and measures always filled up 10 litres or 2 gallons or somesuch here and over there. Crooks aren't always dumb, though they did get caught in the end.

Regards


Martin