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Old 22nd December 2017, 07:58 PM
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Default Bulk Propane Technical Question

Hoping there is a tech guru out there that can clear up a question I have.
House uses LPG from a bulk tank. Coming to the end of my contract thought I would look around for a new supplier.

With that in mind I looked at my usage over the last 19 months. This is what I found:

See attached SS.

http://forum.a8parts.co.uk/attachmen...1&d=1513972935

My question is, how can there be such a discrepancy in the number of litres to a single % between the first and last?

CtL the Confused
Attached Files
File Type: xls flogas-account-activity.xls (26.0 KB, 806 views)
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Currently,
2000 S8, Merlin Purple, Leather Pack 1, Winter Pack 1, SPAX adjustable suspension, AP Racing 6 pot front caliper, 385mm fully floating disks, EBC Yellow Stuff Pads, Black Diamond grooved rear disks and predetor pads, D2 Doctors Brake Block.
1997 4.2 A8SQ - the Projekt. 12 years and ongoing!
1997 4.2 A8SQ - Ming Blue. Restoration sat waiting; saved from the Scrapyard
2003 C5 Allroad 4.2Q - Cobolt Blue. Towing car. Laid up awaiting manual conversion.
2005 C5 Allroad 2.5TDi FE - Grey - Workhorse.
2015 Q3QS SLine - Daytona Grey. Lots of extras! Long Haired Admirals cutter.

Previously
2003 C5 A6 1.9TDI FWD - Loaner from D2 Doctor Lifex
1997 S8 - Ming Blue. Loaned out and written off. I loved that car. My first engine swap after cambelt failure.
1996 4.2 A8SQ - Ming Blue. 178k on a cambelt! Trader's 8. Delivered to A8Parts at Lifex.
2003 2.8 A8SQ - powder blueish. Fill in for a while. Sold on.
1998 1.8T A4 Avant FWD. Ming Blue (there's a theme here), PEX for the 97 S8.
And a list of non VAG going back 40 years before I saw the light.
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  #2  
Old 22nd December 2017, 09:02 PM
MikkiJayne MikkiJayne is offline
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That has to be ambient temperature, especially if you look at the dates - highest volume per 1% is in the winter where the density of the liquid propane is highest. There must be a difference in how the measure volume as it comes of the truck compares to how it behaves once its in the tank - perhaps it comes out as gas but the tank level is showing the liquid?
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Old 23rd December 2017, 07:41 AM
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I can understand that for the small differences but the first delivery?
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Conan (the Librarian)

Watch it if you dare

Currently,
2000 S8, Merlin Purple, Leather Pack 1, Winter Pack 1, SPAX adjustable suspension, AP Racing 6 pot front caliper, 385mm fully floating disks, EBC Yellow Stuff Pads, Black Diamond grooved rear disks and predetor pads, D2 Doctors Brake Block.
1997 4.2 A8SQ - the Projekt. 12 years and ongoing!
1997 4.2 A8SQ - Ming Blue. Restoration sat waiting; saved from the Scrapyard
2003 C5 Allroad 4.2Q - Cobolt Blue. Towing car. Laid up awaiting manual conversion.
2005 C5 Allroad 2.5TDi FE - Grey - Workhorse.
2015 Q3QS SLine - Daytona Grey. Lots of extras! Long Haired Admirals cutter.

Previously
2003 C5 A6 1.9TDI FWD - Loaner from D2 Doctor Lifex
1997 S8 - Ming Blue. Loaned out and written off. I loved that car. My first engine swap after cambelt failure.
1996 4.2 A8SQ - Ming Blue. 178k on a cambelt! Trader's 8. Delivered to A8Parts at Lifex.
2003 2.8 A8SQ - powder blueish. Fill in for a while. Sold on.
1998 1.8T A4 Avant FWD. Ming Blue (there's a theme here), PEX for the 97 S8.
And a list of non VAG going back 40 years before I saw the light.

Last edited by Conan_the_Librarian; 23rd December 2017 at 07:47 AM.
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Old 23rd December 2017, 08:23 AM
paulrstaylor paulrstaylor is offline
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Was the tank empty before the first fill?

The subsequent re-fills were all from about the same point, maybe the gauge isn’t as accurate at 1% or maybe the gas is more compressible as the tank is empty?
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Old 23rd December 2017, 09:54 AM
MikkiJayne MikkiJayne is offline
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I'm sure thats it ^ 1% level on the first fill so the vapour pressure will have been quite low and it'll have been almost all gas. It will have taken more volume to build up the pressure to get the gas to convert to liquid.
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Old 27th December 2017, 12:21 AM
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27litres 27litres is offline
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Is the volume measured at the tank?
Or off the truck?

The base measure of 1% will just be an inaccuracy of however they measure it (float or pressure measure).
It takes quite some pressure to liquify propane, which means quite a volume of gas, and a float measure (which is common in LPG tanks, so possibly in bulk propane tanks too?) will only start to measure once it can float on a liquid. That should explain the initial discrepancy in % full to volume.

You're dealing with a pressure vessel. Volume won't be accurate, as it varies with ambient temperature.
Off the truck is the most accurate measure, as it should be able to measure flow volume, much like an LPG pump does.

Does the tank sit on its side, or vertically?
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2002 Audi S8 - Project
Replacement head coming arrived thanks to MJ
Silver with Black interior. All features as the '01, with the 'S' mode auto shifter. Dodgey rear tint (need to find a way to get rid of that).
Family:
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- has a louder more obnoxious exhaust than the S8, sounds great! Love this thing - Q7 was double the price, and certainly not double the car!

Sold:
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- Hamilton's Club Sport, Achat Grey (will miss the old girl)
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Old 27th December 2017, 06:23 AM
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Bulk propane levels/consumption is a 'black art'. I've had countless 'discussions' with customers over the years with users of LPG powered forklifts and tank volumes/consumption etc.
I've had Calor and Flo-Gas tech guys both explain it to me and it still doesn't make sense!

MJ is on the right track though - it all boils down to temperature on delivery, ambient temp and the likes.
I had a cross reference chart from Calor somewhere giving the volume on LPG as a vapour and as a liquid at different ambient temps.
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2006 Subaru Legacy Spec 'B' 3.0R,
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  #8  
Old 27th December 2017, 09:17 PM
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Conan_the_Librarian Conan_the_Librarian is offline
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Thanks for the replies. The tank was completely empty on that first fill. It sits on its side.
I have a record of daily levels from the tank telemetry. It will vary with temperature, but only by a percentage point or two.
My inept understanding of Boyels law indicates that while it is definitely in liquid form when it leaves the tanker and is counted in fluid litres. When it enters the empty tank it will initially phase change to a gas, but once the tank reaches the prescribed pressure the gas will liquify and all further LPG will remain in liquid form.
While the space for propane in its gaseous state decreases, the pressure will remain constant while it phase changes to liquid as the space is reduced by the incoming liquid. The capicty is then measured by a float.
While the volume of the liquid may change due to temperature it won't be by much; ergo the 1 or 2 % differences.
But 5 (approx) liters per % point? It makes me wonder.....
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Conan (the Librarian)

Watch it if you dare

Currently,
2000 S8, Merlin Purple, Leather Pack 1, Winter Pack 1, SPAX adjustable suspension, AP Racing 6 pot front caliper, 385mm fully floating disks, EBC Yellow Stuff Pads, Black Diamond grooved rear disks and predetor pads, D2 Doctors Brake Block.
1997 4.2 A8SQ - the Projekt. 12 years and ongoing!
1997 4.2 A8SQ - Ming Blue. Restoration sat waiting; saved from the Scrapyard
2003 C5 Allroad 4.2Q - Cobolt Blue. Towing car. Laid up awaiting manual conversion.
2005 C5 Allroad 2.5TDi FE - Grey - Workhorse.
2015 Q3QS SLine - Daytona Grey. Lots of extras! Long Haired Admirals cutter.

Previously
2003 C5 A6 1.9TDI FWD - Loaner from D2 Doctor Lifex
1997 S8 - Ming Blue. Loaned out and written off. I loved that car. My first engine swap after cambelt failure.
1996 4.2 A8SQ - Ming Blue. 178k on a cambelt! Trader's 8. Delivered to A8Parts at Lifex.
2003 2.8 A8SQ - powder blueish. Fill in for a while. Sold on.
1998 1.8T A4 Avant FWD. Ming Blue (there's a theme here), PEX for the 97 S8.
And a list of non VAG going back 40 years before I saw the light.

Last edited by Conan_the_Librarian; 27th December 2017 at 09:23 PM.
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  #9  
Old 27th December 2017, 10:17 PM
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And with the tank on its side you will never get an accurate measure of actual volume using a float due to the cylindrical shape of the pressure vessel.
You could make a fancy circuit or use a computer to try to extrapolate a volume, but no one ever does. Floats just give a level.

Much like trucks with round tanks - those truckies need to watch that last 1/4 tank!
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____________________
Current:
2001 Audi S8 - Brilliant Black with Black interior, C5 RS6 rims (whenever I actually put them on...), Solar Sunroof, Tinted side and rear glass, RNS-D, Grom, Bose, clunky old phone in arm rest!
2002 Audi S8 - Project
Replacement head coming arrived thanks to MJ
Silver with Black interior. All features as the '01, with the 'S' mode auto shifter. Dodgey rear tint (need to find a way to get rid of that).
Family:
2009 Volvo XC90 V8 R Design
- has a louder more obnoxious exhaust than the S8, sounds great! Love this thing - Q7 was double the price, and certainly not double the car!

Sold:
1997 Audi A4
- Hamilton's Club Sport, Achat Grey (will miss the old girl)
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  #10  
Old 28th December 2017, 07:13 AM
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Ameiseuk Ameiseuk is offline
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The only really accurate way to measure is in the same way the gas suppliers meter the delivery normally via a paddle wheel flow meter.

In theory the volume supplied should equal the volume drawn off in a liquid format.
Only downside to all this is getting hold of an EX rated flow meter - and fitting it to the pipework. A truck breaker might help if they have an old calor LPG tanker with the pumping equipment still on it
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Daily drive:
2016 Infiniti QX70.....a car that's even more complicated than my last Infiniti FX to modify

Current 'Project':
VW Crafter CR50 4 berth camper van

Previous 'Projects':
2006 Subaru Legacy Spec 'B' 3.0R,
1994 Ex-MOD Land Rover Defender, now "civilianised".
2000 Audi S8 FL

www.whall.co.uk
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