Brim to brim...

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Pinger
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Re: Brim to brim...

#61 Post by Pinger » Sat Nov 07, 2020 8:49 pm

Gilbertd wrote:
Sat Nov 07, 2020 8:33 pm
]No, neither have I and I bet if you ever did find one, it'll be an arm and leg to buy.
I always ask the easy questions first....
Gilbertd wrote:
Sat Nov 07, 2020 8:33 pm
My car is fitted with what the label says is a Bigas Pegaso but with Leo written on it in felt pen and only the AEB Leonardo software will connect (so I suspect it has been flashed with Leonardo firmware at some point in the past). My other car is fitted with an OMVL Millennium one so only the Millennium software will connect but they both respond and operate in exactly the same way.
Millenium on mine.
I guess I'm noticing the jump to default on mine when it enters the second TPS box because of how far it has to jump!
It's how fast it can move though that is surprising - and useful.

There's other stuff that LPGC mentioned - like the reactions being faster with increased rpm. Maybe that is it reacting to O2 readings he is referring to which increased gas speed through the manifold would help in reducing delay in the signal being sent to the ECU.

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Re: Brim to brim...

#62 Post by Pinger » Sat Dec 05, 2020 2:59 pm

The temperature the tank is at seems to have quite an effect on how much LPG it will accept.
When I first filled mine the difference between the 4th light switching on/off and fully filled was 14 litres on a balmy afternoon mid March. The same prevailed for most of the year. Filled it on Thursday morning after it had sat outside all night in sub zero temps (for the rest of the day it never rose beyond minus 3C) and before the tank had taken any heat from the cabin. It swallowed 26 litres for the same increment (between the 4th light switching on/off and fully filled).
An additional 12 litres and the tank filled to 90% of capacity by my calculation. I'm kind of thinking that at that I need to go driving immediately and burn some off. Leaving it sat in the sun wouldn't be the smartest thing to do - or is that well within what the tank can withstand?

Does the density of liquid LPG (as it sits in the supply tank) vary greatly with temperature? IIRC, petrol does more than diesel (petrol being more volatile) and LPG is more volatile than both of them. The tank I draw from sits outside - exposed to the sun. Two reasons to re-fuel first thing in the morning rather than the old petrol habit of doing it at the end of the day?

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Re: Brim to brim...

#63 Post by LPGC » Sat Dec 05, 2020 3:31 pm

Some forecourt pumps use ambient temperature (or forecourt bulk tank temp) as a reference temperature, the temperature reading then effects forecourt pump pressure.. Or the fourecourt pump may just add a few bars of pressure to forecourt tank pressure. Assuming the vehicle tank is at the same temperature as the forecourt tank this makes for consistent fill speed because the pressure difference between pump and vehicle is around the same irrespective of weather etc. Some forecourt pumps have a pressure gauge, where one is fitted you'll usually see the gauge reads higher pressure in warmer weather and vice/versa. The fastest tank fills happen when the difference between pump pressure and tank pressure is greatest... Sometimes you'll find a forecourt pump that pushes 13 bar in cold winter conditions when tank pressure might only be 4 or 5 bar, this will make for a very quick fill because the pressure difference between pump and tank is (in this example) 8 or 9 bar when usually the difference might only be 3 or 4 bar.

Still you will be able to put more gas in the tank in cold conditions than warm conditions because (like you've said) the liquid gas expands with rising temperature (density of liquid decreases). On a lot of LPG pumps there are words to the effect 'calibrated for gas at 15degC'.... We buy gas by weight really, not volume. If we buy a litre's worth of gas in cold conditions we may not get quite a full litre by volume, if we buy a litre of gas in warm conditions we may get a bit more than a litre in volume but we'd be buying the same weight of gas and paying for the correct amount of gas on both occasions. Which means that for example if we buy 70 litres of cold gas it may not be enough volume to make the vehicle tank float rise enough to shut off incoming gas but on a warm day 68 litres may be all we can get in the vehicle tank, you may get a bit more gas in the tank in cold conditions than in warm conditions.

However, there is an aspect that can prevent LPG tanks filling to even float shut-off level in cold conditions. Air pressure in the tank (air trapped in the tank before the tank was sealed) can be the limiting factor that prevents the pump pushing any more gas into the tank. If a tank is sealed then we fill it to 80% with a liquid the air is going to be compressed into 1/5 of it's original volume so now the tank has 5 bar pressure (4 bar on top of atmospheric) even if the liquid is only water. For a 90% fill the air is going to be compressed into 1/10th of it's original volume so now we have 9 bar air pressure relative to atmospheric pressure - an LPG pump that only pushes 8 bar in cold conditions could never pump gas into a tank that has higher than 8 bar pressure (and even as pressure approaches 8 bar the speed of fill will drop to a slow trickle). In fact whenever air pressure in the tank means tank pressure is higher than (would be) gas pressure (if the tank didn't contain any air) it will slow the speed of the tank fill. You don't really notice the slower fill if the tank only fills to 80% because gas pressure in the tank is seldom below 5 bar because the weather usually isn't cold enough but if the tank valve has been modded to allow the tank to fill to more than 80% and/or weather is cool you do notice the difference in fill speed (and capacity) if there is any air in the tank. Where possible when I do a new install I flush air out of the tank, just put a couple of litres of gas in the tank then let it out (let it out in vapour form not liquid form), air comes out with the gas vapour. I also always modify the tank float to allow the tank to fill to 90% (or on my own cars to 100%).

On one of my own vehicles I have a 93L rated (water capacity) tank fitted, I have intentionally disabled the tank float shut off mechanism on this car, the other day in cold conditions I got 95 litres in the 93L tank lol. If I didn't use any of that gas out of the tank and just left it full to the brim until spring when the weather warmed up the tank would vent some of that gas, but as soon as I'd filled up I payed the cashier and drove away thus immediately started using some of that gas. The pump I filled at didn't have a pressure gauge but didn't fill the tank particularly quickly, so I imagine it's pressure would only have been (say) 8 bar. If I hadn't removed the air from this tank before I fitted it rising air pressure in the tank (as liquid gas level rose as I filled the tank) would have meant I'd only have been able to fill the tank to around 92% full (around 85 litres) even though I'd disabled the tank fill limiter with intention of allowing it to fill to 100%. With air in the tank I might have been able to fill the tank to a greater percentage of full in summer (when gas and pump pressure are highest but air pressure remains almost constant) than in winter, removing air means I can fill to the same percentage of full regardless of weather but I can still get more gas in my tank in winter because that is when liquid gas is most dense.

Over time the amount of air in a tank can change anyway. Usually when we draw gas from the tank we only draw liquid but when the tank is nearly empty of liquid some systems can run on vapour at low engine loads (particularly mixer systems and particularly on small engines), if the engine is fed on vapour from the tank some of that vapour will be air mixed with gas, so some air can be removed from the tank in these conditions. On the other hand most sequential systems have reducer output pressure referenced to manifold pressure and the manifold can be under vacuum, so on a small engine with a sequential system and reducer output pressure referenced to manifold pressure if we set too low a pressure for the system to switch back to petrol we could have a situation where tank pressure is even slightly below atmospheric pressure while we're running on vapour, which then might cause one way fill valves on the tank to open to allow air into the tank. E.g. if map is 0.26 bar while an engine is idling and a sequential system is set to switch back to petrol at 0.4 bar pressure tank pressure could fall to 0.66 bar before the system switches back to petrol, which is 0.34 bar of vacuum in the tank. This could only happen if the engine were left idling but still for this reason I don't set changeover pressure below 0.7 bar. Even though mixer systems are more likely to be able to run on vapour than a sequential system you won't have a situation with extremely low tank pressure on a mixer system because the mixer system doesn't have output pressure referenced to manifold pressure (except on a turbo), their reducers are referenced to atmospheric pressure. A tiny bit of air will get into the tank when the connection is made between forecourt pump and vehicle filler.
Last edited by LPGC on Wed Dec 09, 2020 10:44 am, edited 5 times in total.
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Re: Brim to brim...

#64 Post by Pinger » Sat Dec 05, 2020 4:30 pm

LPGC wrote:
Sat Dec 05, 2020 3:31 pm
Some forecourt pumps use ambient temperature (or forecourt bulk tank temp) as a reference temperature, the temperature reading then effects forecourt pump pressure.. Or the fourecourt pump may just add a few bars of pressure to forecourt tank pressure. Assuming the vehicle tank is at the same temperature as the forecourt tank this makes for consistent fill speed because the pressure difference between pump and vehicle is around the same irrespective of weather etc. Some forecourt pumps have a pressure gauge, where one is fitted you'll usually see the gauge reads higher pressure in warmer weather and vice/versa. The fastest tank fills happen when the difference between pump pressure and tank pressure is greatest... Sometimes you'll find a forecourt pump that pushes 13 bar in cold winter conditions when tank pressure might only be 4 or 5 bar, this will make for a very quick fill because the pressure difference between pump and tank is (in this example) 8 or 9 bar when usually the difference might only be 3 or 4 bar.
My tank might even have been colder than the supply tank - which at least saw some sunlight!
At the other end of the day when my in-cabin tank is as warm as the interior after a day's driving I'm not going to get the same fill capacity.
LPGC wrote:
Sat Dec 05, 2020 3:31 pm
Still you will be able to put more gas in the tank in cold conditions than warm conditions because (like you've said) the liquid gas expands with rising temperature (density of liquid decreases). On a lot of LPG pumps there are words to the effect 'calibrated for gas at 15degC'.... We buy gas by weight really, not volume. If we buy a litre's worth of gas in cold conditions we may not get quite a full litre by volume, if we buy a litre of gas in warm conditions we may get a bit more than a litre in volume but we'd be buying the same weight of gas and paying for the correct amount of gas on both occasions. Which means that for example if we buy 70 litres of cold gas it may not be enough volume to make the vehicle tank float rise enough to shut off incoming gas but on a warm day 68 litres may be all we can get in the vehicle tank, you may get a bit more gas in the tank in cold conditions than in warm conditions.
That's the reverse of how petrol and diesel is sold which is volumetrically and tough luck if the fuel is warm and you get a lighter litre.
We always get the full amount by mass with LPG?
LPGC wrote:
Sat Dec 05, 2020 3:31 pm
However, there is an aspect that can prevent LPG tanks filling to even float shut-off level in cold conditions. Air pressure in the tank (air trapped in the tank before the tank was sealed) can be the limiting factor that prevents the pump pushing any more gas into the tank. If a tank is sealed then we fill it to 80% with a liquid the air is going to be compressed into 1/5 of it's original volume so now the tank has 5 bar pressure (4 bar on top of atmospheric) even if the liquid is only water. For a 90% fill the air is going to be compressed into 1/10th of it's original volume so now we have 9 bar air pressure relative to atmospheric pressure - an LPG pump that only pushes 8 bar in cold conditions could never pump gas into a tank that has higher than 8 bar pressure (and even as pressure approaches 8 bar the speed of fill will drop to a slow trickle). In fact whenever air pressure in the tank means tank pressure is higher than (would be) gas pressure (if the tank didn't contain any air) it will slow the speed of the tank fill. You don't really notice the slower fill if the tank only fills to 80% because gas pressure in the tank is seldom below 5 bar because the weather usually isn't cold enough but if the tank valve has been modded to allow the tank to fill to more than 80% and/or weather is cool you do notice the difference in fill speed (and capacity) if there is any air in the tank. Where possible when I do a new install I flush air out of the tank, just put a couple of litres of gas in the tank then let it out (let it out in vapour form not liquid form), air comes out with the gas vapour. I also always modify the tank float to allow the tank to fill to 90% (or on my own cars to 100%).
Glad I didn't have to contend with trapped wind! But then I'm assuming my tank has been run so low as to emit gas (and air) during its life or was purged initially in the manner you do it. No way of knowing I suppose.

LPGC wrote:
Sat Dec 05, 2020 3:31 pm
On one of my own vehicles I have a 93L rated (water capacity) tank fitted, I have intentionally disabled the tank float shut off mechanism on this car, the other day in cold conditions I got 95 litres in the 93L tank lol. If I didn't use any of that gas out of the tank and just left it full to the brim until spring when the weather warmed up the tank would vent some of that gas, but as soon as I'd filled up I payed the cashier and drove away thus immediately started using some of that gas.
So it can actually vent in that situation. Is that via different provision from the (fusible?) one that vents in the event of fire or the same? Is either (assuming separate) self sealing after venting?

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Re: Brim to brim...

#65 Post by LPGC » Sat Dec 05, 2020 4:46 pm

Yes the tank will at least fill a bit slower if it's warmer because it's pressure will be higher if warmer. On the other hand as you use gas from the tank the headroom above liquid increases and some liquid has to boil to maintain tank pressure, the boiling has a cooling effect on the tank... so the tank can be cooler than the vehicle interior the extent of which can depend on how much gas you're using (how far you've had your foot down).

I thought even petrol and diesel pumps are calibrated for volume at a set temperature?

Trapped wind is more of a cng thing than lpg lol..

The pressure relief valve and fusible link might be in the same component (parts of a multivalve or parts of a 4 hole tank single valve) but the over-pressure valve part will close when pressure has fallen, where-as the heat fusible part will fuse and stay open if you throw the tank on a bonfire.
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Re: Brim to brim...

#66 Post by Pinger » Sat Dec 05, 2020 5:17 pm

LPGC wrote:
Sat Dec 05, 2020 4:46 pm
Yes the tank will at least fill a bit slower if it's warmer because it's pressure will be higher if warmer. On the other hand as you use gas from the tank the headroom above liquid increases and some liquid has to boil to maintain tank pressure, the boiling has a cooling effect on the tank... so the tank can be cooler than the vehicle interior the extent of which can depend on how much gas you're using (how far you've had your foot down).
And I give up some of my cabin heat to it. No matter, Vortecs have heaters like furnaces. Two of them in a Suburban,
LPGC wrote:
Sat Dec 05, 2020 4:46 pm
I thought even petrol and diesel pumps are calibrated for volume at a set temperature?
They will be - but above that temp you don't get the mass, below you score and get more. There's no correction available.
It must be the same with LPG - but more so? No?
LPGC wrote:
Sat Dec 05, 2020 4:46 pm
Trapped wind is more of a cng thing than lpg lol..
No comment!
LPGC wrote:
Sat Dec 05, 2020 4:46 pm
The pressure relief valve and fusible link might be in the same component (parts of a multivalve or parts of a 4 hole tank single valve) but the over-pressure valve part will close when pressure has fallen, where-as the heat fusible part will fuse and stay open if you throw the tank on a bonfire.
I thought the fire one was once opened it stats open. The lower pressure vent sounds quite safe (but for the slight leakage).

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Re: Brim to brim...

#67 Post by LPGC » Sat Dec 05, 2020 5:52 pm

The fire one is once open it stays open, the pressure one will re-close at lower pressure.

Obviously I wouldn't be able to get 95L in a 93L tank, but I can get the same mass of 95L of LPG at 15degC in a 93L tank in cold weather when LPG is denser... But regardless of temp I pay for the correct mass of gas, just that the pump sells in terms of volume corrected for 15degC, which is just the same as buying by mass. Either that or the pump over-charged me ;-) I'm sure not all pumps are completely accurate but I believe this pump was accurate on this occasion.

You won't give up much cabin heat even if you're booting it. Could do the maths but some AC systems use propane as refrigerant and I expect they're pumping quite a lot more propane than the speed at which the engine will use gas (again as you'll know it isn't the engine using gas from the tank that causes the tank to cool, it is the increasing headroom in the tank as liquid gas is drawn from the tank that causes the tank to cool as it is this that causes some liquid to boil to maintain tank pressure - half the cooling effect on the tank of drawing vapour from the tank, if we draw vapour from the tank the tank is cooled not only by liquid boiling to maintain tank pressure as headroom increases but also directly by the gas boiling that is used as vapour - the same amount of cooling as a pressure reducer in the engine bay is subjected to).
Last edited by LPGC on Wed Dec 09, 2020 3:45 pm, edited 3 times in total.
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Re: Brim to brim...

#68 Post by Gilbertd » Sat Dec 05, 2020 6:20 pm

LPGC wrote:
Sat Dec 05, 2020 5:52 pm
Could do the maths but some AC systems use propane as refrigerant
If you look at your fridge and see that it is using R290 refrigerant, that's Propane and is quite common. Others use R600A which is isoButane. Refrigerant pressure varies with temperature but at an ambient of 25 degrees C the compressor in an R290 system will be running at around 10 bar, to convert vapour back to liquid in the condenser. Rumour has it that R290 can be used as a drop in replacement for R12 in pre-93 automotive AC systems.
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Re: Brim to brim...

#69 Post by Pinger » Sun Dec 06, 2020 11:04 am

LPGC wrote:
Sat Dec 05, 2020 5:52 pm
Obviously I wouldn't be able to get 95L in a 93L tank, but I can get the mass of 95L at cold temp (so volume is smaller) in a 93L tank... But regardless of temp I pay for the correct mass of gas, just that the pump sells in terms of volume corrected for 15degC, which is just the same as buying by mass. Either that or the pump over-charged me ;-) I'm sure not all pumps are completely accurate but I believe this pump was accurate on this occasion.
Surely the correct mass is delivered only at 15C? Below 15C the fuel is denser but the pump dispenser (with very probably a paddle type flow meter) can only measure volume so misses the increased density and delivers a greater mass of fuel and at above 15C the density will be lower so less mass delivered for the litres showing on the display. Unless the metre reading adjust with changes in ambient temp.
LPGC wrote:
Sat Dec 05, 2020 5:52 pm
You won't give up much cabin heat even if you're booting it. Could do the maths but some AC systems use propane as refrigerant and I expect they're pumping quite a lot more propane than the speed at which the engine will use gas (again as you'll know it isn't the engine using gas from the tank that causes the tank to cool, it is the increasing headroom in the tank as liquid gas is drawn from the tank that causes the tank to cool as it is this that causes some liquid to boil to maintain tank pressure - half the cooling effect on the tank of drawing vapour from the tank, if we draw vapour from the tank the tank is cooled not only by liquid boiling to maintain tank pressure as headroom increases but also directly by the gas boiling that is used as vapour - the same amount of cooling as a pressure reducer in the engine bay is subjected to).
It aint freezing me out - thankfully! It hadn't occurred to me that it would draw heat (despite being well aware of the thermodynamics of the process!) until the thread last week about the 28 stoves in a 7 storey building. Some comments there let it dawn on me.
The biggest practical consequence of all this as it applies to my truck with its tank in the cabin is that if I've driven all day with a toasty hot cabin the tank will accept less if I then go and re-fuel compared to when I do it first thing in the morning with the cabin still stone cold. It points to an advantage an external (under floor) tank may have. But not I suppose if all the cooling air from the engine and transmission passes over it. The only set-up that strikes me as being immune to all of this is the pick-up with a tank mounted at the front of the bed behind the cab.
The difference in extra fuel taken on board at minus 3C on Thursday was an additional 30 miles of range - not insignificant.

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Re: Brim to brim...

#70 Post by Pinger » Sun Dec 06, 2020 11:12 am

Gilbertd wrote:
Sat Dec 05, 2020 6:20 pm
LPGC wrote:
Sat Dec 05, 2020 5:52 pm
Could do the maths but some AC systems use propane as refrigerant
If you look at your fridge and see that it is using R290 refrigerant, that's Propane and is quite common. Others use R600A which is isoButane. Refrigerant pressure varies with temperature but at an ambient of 25 degrees C the compressor in an R290 system will be running at around 10 bar, to convert vapour back to liquid in the condenser. Rumour has it that R290 can be used as a drop in replacement for R12 in pre-93 automotive AC systems.
I didn't know that refrigerants were so similar (if not identical) to our fuels.
I was aware of the danger from old fridges that leak and then a spark on start up ignites the leaked gas - I see why it so dangerous now (the root of the original fire in Grenfell Towers?). I'm guessing the propane doesn't have the added smell that gas as fuel has. (Mercaptan - when the St Fergus gas terminal (not so very far from where I'm based) had to open its mercaptan tank for cleaning it issued a press release in advance warning the public. I made sure I was nowhere near with that going on).

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Re: Brim to brim...

#71 Post by Gilbertd » Sun Dec 06, 2020 2:06 pm

R290 doesn't have the smelly stuff in it and no moisture or lubricant so is must better quality than what we get from the forecourt pumps. All refrigerants do the same job so they all have very similar characteristics. I did my AC FGas course a few months ago and knowledge of how the LPG system on a car helped in understanding it, although the terminology was confusing. As far as I'm concerned the evaporator gets cold (due to the liquid vaporising) so no different to what happens in our vaporiser but they refer to it as drawing heat rather than cooling down. As it passes through the compressor, the vapour is compressed until it turns back into a liquid in the condenser but the AC industry refers to it as a superheated liquid. To me superheating it would mean passing it through a heater of some sort rather than it generating heat due to it being compressed. Refrigerants have different boiling points and different ones are used for different applications depending on the temperature ranges needed. So what is used in a deep freeze system will be different to that used in an AC system. A modern domestic AC system using R32 (the current approved refrigerant) will run down to around 8 degrees C, so not cold enough for a deep freeze that needs to run down to -15 C or so. Then there's also the GWP (Global Warming Potential) of the refrigerant and there's regulations regarding that (Montreal and Kyoto protocols) so the lower the GWP the more acceptable the refrigerant. Other difference is compatibility with other components. When car systems changed from R12 (which has a ridiculously high GWP of 10,900) to R134a (GWP 1430), you couldn't simply refill a system with the later gas. Or at least you could, and some people did, but it's not a good idea as an R12 system used a mineral oil to lubricate the compressor and R134a causes mineral oil to turn to jelly. You can change to PAG (Polyalkylene Glycol) oil, which is compatible with the R134a, but it isn't compatible with the seals and O rings used in an R12 system so the compressor and pipe joints will start to leak.
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93 Range Rover 4.2LSE, Lovato LovEco, sold
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Re: Brim to brim...

#72 Post by Pinger » Sun Dec 06, 2020 3:00 pm

Sounds like a mixture of terminologies used on your course. 'Superheated' is a term usually reserved for steam when it is heated way beyond the temperature required to boil the water it came from irrespective of the pressure it is at and is used by those who run steam plant eg, steam turbines. Your intuitive understanding is pretty much correct as in creating superheated steam heat is added in a particular part of the boiler to enable that. The pressures are such that boiler construction is very expensive and failure catastrophic. Browsing 'steam tables' gives a good insight into the 'saturation' pressures and temperature of steam. The principles there are broadly applicable to all fluids/gases.
'Drawing heat' is because in thermodynamics there is no concept of cold. Cold is merely an absence of heat in the same way that darkness is merely an absence of light.

The rest of your post reminds why I'm quite happy to have ditched my AC. I really couldn't be bothered resurrecting a 21 year old system with two evaporators and 40 foot of hoses. In Scotland, I just don't need it. On the American truck forum I frequent - in some states functioning AC is everything!

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Re: Brim to brim...

#73 Post by LPGC » Sun Dec 06, 2020 4:46 pm

I've worked on power stations in the past, been everywhere inside them, familiar with the design of the boilers and may still have the blueprint for one somewhere.

Suppose having the LPG tank inside will mean it's warmer in cold weather but could mean it's colder than outside in warm weather if your aircon was working. An external tank will get airflow around it, there will be conditions where airflow could mean the tank doesn't get quite so cold if it's outside compared to inside. But I think in most conditions we don't need to concern ourselves much with tank temp, in my experience the only problems occur when the tank is comparatively small for the weight of the vehicle and power of the engine (when the engine is repeatedly booted), which can cause the tank to cool lowering it's pressure, there's then less pressure to push gas to the reducer - but I'm talking continually booting 400bhp + vehicles.

The pumps may use a paddle to meter the volume of liquid LPG they're pumping in but there's nothing to stop them having a temp sensor next to the paddle. I expect a modern forecourt pump won't have a direct mechanical connection between paddle and litres reading, more likely electronics monitor paddle movement and display temp compensated litres? I have definitely filled with LPG using old-skool pumps that have direct connection between paddle and meter reading in the past but not on normal type forecourts, I'm thinking more man with a bulk LPG tank and pump type setups - imagine could get a bargain filling with LPG at such place in very cold weather.
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Re: Brim to brim...

#74 Post by Pinger » Sun Dec 06, 2020 5:35 pm

I'll pay more attention to the set-up I fuel from and take a photo if I remember and post here. It's the only LPG pump I've used so have no idea how modern. This is rural Scotland though.... (take your mobile phone signal home in a bucket sort of place where the snails go door to door because it's faster than sending a text).

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Re: Brim to brim...

#75 Post by Brian_H » Sun Dec 06, 2020 5:53 pm

The really old pumps (and there are a handful of them still about) are mechanical on the meter and have a winder on the side to set them back to zero before you start. Last time I remember using one of those was at Autotech in Ripley. The more modern ones would tend to have a digital electronic display which the majority of the ones seen now are. As said above if they are the man and tank type setup (or the sort of place where the lpg tank and pump is off the side of a forecourt not under the canopy and with a very basic connection to the shop - a CCTV camera pointed at the pump display to allow the cashier to see how much as been dispensed for example) then they might not have any real temp correction. The majority of them do have the sticker about 15 degrees C though that I've used.

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Re: Brim to brim...

#76 Post by Pinger » Sun Dec 06, 2020 6:10 pm

Yes - that's the set-up. Just around the corner - if you see the toilets, you've gone too far. It is LCD and coupled to the cashier's desk though. The CCTV is to stop bottle filling and let them know there's a customer there I think.
Genuinely, I had no idea the temp compensation was used. Is this the case for petrol and diesel as well these days?

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Re: Brim to brim...

#77 Post by LPGC » Mon Dec 07, 2020 10:57 am

Pinger wrote:
Sat Dec 05, 2020 4:30 pm

At the other end of the day when my in-cabin tank is as warm as the interior after a day's driving I'm not going to get the same fill capacity.
I forgot to answer this one. Don't forget that the tank might weigh 20kg but the gas you're putting in might weigh 40kg (the gas you put in the tank weighs more than the tank itself). What I'm getting at is that as you fill the tank with liquid gas at a certain temperature it's going to change the tank temperature - cool it if the tank is warm and incoming gas is cooler, warm it if the tank is very cold and the incoming gas is warmer. In any case it's the temperature of the gas that matters not of the tank itself, tank temp only matters because it will pull gas temperature. In most conditions tank temp will be the same as gas temp but temps may differ most for a short time in certain conditions while filling.

There's another effect too, if the tank is at low pressure (because it's empty of liquid) and/or warm the incoming liquid gas will boil as it enters the tank and the evaporation will have a cooling effect. As said above I often put a few litres in a new tank in the yard before I fit it tank. To get the few litres in the tank I just connect the outlet from another tank to the inlet of the new tank. Both tanks start at ambient temperature but both tanks are cooled during the process, especially the recipient (new) tank which in winter conditions will often have ice forming on the outside of it due to incoming gas boiling as soon as it enters the recipient (lower pressure) tank. On a forecourt with the tank cooled by initial incoming gas before the bulk of the fill it remains cooler than ambient temperature throughout the fill but raises toward somewhere between ambient temp and incoming gas temp as the tank fills.. but it may still be cooler than ambient and/or incoming gas temp at the end of the fill and on average throughout the process will be cooler than average of incoming gas and ambient temp.

Obviously this is an over simplified explanation and ignores things like specific heat capacities but it gives an idea of some of the things going on and how they can effect fill speed etc.
Last edited by LPGC on Wed Dec 09, 2020 10:54 am, edited 2 times in total.
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Pinger
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Re: Brim to brim...

#78 Post by Pinger » Mon Dec 07, 2020 12:01 pm

Thanks LPGC. I'll give that some thought and see how to best maximise my fill. Typically a working day for me involves a 100-130 mile run. If I could get two days from one tankful it would be a useful time saver (just from the stop and the payment aspect though I mainly pass the filling station anyway). For longer trips, as much as range as possible is worth pursuing.

A quick question you might be able to answer. Is superheated steam as corrosive as I'm led to believe? Relative to the materials used in the exhaust turbine of a turbocharger, how much better specified do materials in contact with superheated steam need to be - or is the turbo the more demanding application?

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Re: Brim to brim...

#79 Post by LPGC » Mon Dec 07, 2020 12:22 pm

Perhaps the best way of maximising range from your current setup (assuming mixture etc is already correct so the engine is running most efficiently) would be to bend the float arm in your tank so your tank will take more gas.

I don't know much about the corrosion causing properties of steam but I'd expect the turbo is the more demanding application. There is steam in exhaust gasses of an engine burning a hydro-carbon fuel anyway. Steam engines were quite reliable and steam turbines in power stations were reliable for a long time before car turbos became reliable, few applications would see steam reach engine exhaust gas temperatures?
Full time LPG installer
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2 miles A1, 8 miles M62,
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Pinger
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Re: Brim to brim...

#80 Post by Pinger » Mon Dec 07, 2020 1:45 pm

LPGC wrote:
Mon Dec 07, 2020 12:22 pm
Perhaps the best way of maximising range from your current setup (assuming mixture etc is already correct so the engine is running most efficiently) would be to bend the float arm in your tank so your tank will take more gas.
Not so desperate as want to open up the tank but your point is valid.
Re efficiency - the AFR meter should show me instances of unnecessary rich mixtures (if present) which I can attempt to dial out - partly why I want it installed. I have the enrichment at TPS > threshold value set quite crudely. A bit of finessing there in tune with the gearbox kick down characteristics is possibly fruitful.
LPGC wrote:
Mon Dec 07, 2020 12:22 pm
I don't know much about the corrosion causing properties of steam but I'd expect the turbo is the more demanding application. There is steam in exhaust gasses of an engine burning a hydro-carbon fuel anyway. Steam engines were quite reliable and steam turbines in power stations were reliable for a long time before car turbos became reliable, few applications would see steam reach engine exhaust gas temperatures?
This forum so badly needs a 'like' button - cheers!

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