Gas regulator pressure gauges……

[Graham_Wright]

……do they give any indication of cylinder contents?

It seem to me they just measure the pressure of vaporisation of the liquid gas. Or have I forgotten more than I realise?

 

[NickRobinson]

……do they give any indication of cylinder contents?

It seem to me they just measure the pressure of vaporisation of the liquid gas. Or have I forgotten more than I realise?

no, that's correct, until the cylinder is empty, but you'll know that anyway. Weighing the cyl works http://www.ebay.co.uk/itm/40kg-10g-...503270?hash=item2374ec5f26:g:jQEAAOSwzaJYBQVc

 

[Graham_Wright]

no, that's correct, until the cylinder is empty, but you'll know that anyway. Weighing the cyl works http://www.ebay.co.uk/itm/40kg-10g-...503270?hash=item2374ec5f26:g:jQEAAOSwzaJYBQVc

That's a relief then it's always nerve wracking when making bold technical statements!

Mine is a pivoting locker so I could measure the pressure opposite the hinge (and even have a remote reading with a bit of electrickery.

 

[vyv_cox]

Or you can measure the liquid level with a Truma or similar contents gauge. Doesn't work on Camping Gaz 907 bottles but good for bigger ones. Also measures diesel level in steel tanks.

 

[GHA]

no, that's correct, until the cylinder is empty, but you'll know that anyway. Weighing the cyl works http://www.ebay.co.uk/itm/40kg-10g-...503270?hash=item2374ec5f26:g:jQEAAOSwzaJYBQVc

To add another question just out of interest....

If it's a mixture of butane /propane is the pressure linear? Like half butane / half propane will it be half way between the pressure of each gas?
Had that before somewhere in caribbean and always wondered... Ta

Grp bottles are dead handy for seeing how much gas is left

 

[NickRobinson]

To add another question just out of interest....

If it's a mixture of butane /propane is the pressure linear? Like half butane / half propane will it be half way between the pressure of each gas?
Had that before somewhere in caribbean and always wondered... Ta

Grp bottles are dead handy for seeing how much gas is left

Good question.. At first I thought the question was along the lines of- 'Is the pressure at one end of the balloon higher than the other?'

Instinct (ha!) suggests the higher vapour pressure will win out?

 

[GHA]

Google says this,,,

http://www.engineeringtoolbox.com/propane-butane-mix-d_1043.html

 

[rogerthebodger]

Google says this,,,

http://www.engineeringtoolbox.com/propane-butane-mix-d_1043.html

The real answer to measuring the contents at any LPG cylinder is to weigh the contents without including the weight of the cylinder. The weight of the cylinder varies with the construction but the weight of the contents when full is defined.

We have cylinders the contain 9Kg of LPG but in the UK it may be more like 4.5 Kg.

The trick is to have a scale that can be set to full and then as the weight reduces the gauge indicator reduces until in my case 9 kgs have been used then the gauge should read empty.

Most scales are designed to be set to zero then to increase as weight is added.

The answer is to have a micro controlled scale that can be set to full when a full cylinder is placed on the scale then as the weight reduces the micro changes the output reading until the LPG weight has been used.

I am sure that one of the micro programming guys can do such a program for say a Arduino that can display on a standard "fuel" gauge.

I have been thinking about this for some time but my programming skills are too out of date now.

 

[Graham_Wright]

The answer is to have a micro controlled scale that can be set to full when a full cylinder is placed on the scale then as the weight reduces the micro changes the output reading until the LPG weight has been used.

I am sure that one of the micro programming guys can do such a program for say a Arduino that can display on a standard "fuel" gauge.

I have been thinking about this for some time but my programming skills are too out of date now.

How about a strain gauge and a standard analogue meter?

 

[GHA]

The real answer to measuring the contents at any LPG cylinder is to weigh the contents without including the weight of the cylinder.

I find it much easier just looking at the side of the bottle to see where the level of the liquid is..

GRP bottle of course, to quite as easy for those with steel bottles.

 

[Graham_Wright]

I find it much easier just looking at the side of the bottle to see where the level of the liquid is..

GRP bottle of course, to quite as easy for those with steel bottles.

Even if it were grp, it is inaccessible so a non starter for me.

 

[rogerthebodger]

Even if it were grp, it is inaccessible so a non starter for me.

And for me. We only have steel LPG bottle any way.

 

[[163233]]

I'm sure I saw temperature gauges that you stick on the side of the bottle somewhere. You'd have to be burning off gas to get a measurable cold spot I guess?

 

[GrahamM376]

……do they give any indication of cylinder contents?

As others have said, no. Big advantage though is they're the best leak detector around as they monitor complete system after the cylinder valve, unlike bubble leak.

 

[vyv_cox]

I'm sure I saw temperature gauges that you stick on the side of the bottle somewhere. You'd have to be burning off gas to get a measurable cold spot I guess?

Yes, I have never found mine to be much use in a larger bottle. They kind of work in a 907 but there is always a certain amount of guesswork about it.

 

[superheat6k]

To add another question just out of interest....

If it's a mixture of butane /propane is the pressure linear? Like half butane / half propane will it be half way between the pressure of each gas?
Had that before somewhere in caribbean and always wondered... Ta

Grp bottles are dead handy for seeing how much gas is left

The answer to your question is incredibly complex and requires detailed knowledge to thermodymamics and the gas laws, Boyles Law, Law of partial pressures and a few others. However, Vyv's table is probably easier to follow.

The result will sit somewhere between the two but not necessarily exactly halfway.

Fuel gases such as propane and butane act much the same way as refrigerant gases, where blended mixtures are the most commonly used gases in industry, e.g R410A, R407C, R4 anything. Indeed iso-butane is commonly used in domestic fridges.

Well you did ask !

 

[TLouth7]

If it's a mixture of butane /propane is the pressure linear? Like half butane / half propane will it be half way between the pressure of each gas?

Presumably given the difference in vapour pressure, the ratio of gases will not be the same as the ratio of liquid (more propane vapour). This would result in more propane being burnt at first, and so the ratio of liquid would change over time [1].

As the proportion of propane decreases the total vapour pressure will decrease as per GHA's graph, so for a given temperature the measured pressure would tell you the ratio remaining in the bottle [2].

You would probably need to know the full temperature and pressure history to convert this ratio into a value for how much is left, so it might be simpler just to install an in-line gas meter.

[1] This is the same as how a spirit still brings over more ethanol at first.
[2] I believe this would be linear as the total vapour pressure is the sum of the partial pressures of the two fluids, so with say 20% butane, you would have the vapour pressure of butane at that temp x 0.2 + vapour pressure of propane x 0.8

 

[superheat6k]

Presumably given the difference in vapour pressure, the ratio of gases will not be the same as the ratio of liquid (more propane vapour). This would result in more propane being burnt at first, and so the ratio of liquid would change over time [1].

As the proportion of propane decreases the total vapour pressure will decrease as per GHA's graph, so for a given temperature the measured pressure would tell you the ratio remaining in the bottle [2].

You would probably need to know the full temperature and pressure history to convert this ratio into a value for how much is left, so it might be simpler just to install an in-line gas meter.

[1] This is the same as how a spirit still brings over more ethanol at first.
[2] I believe this would be linear as the total vapour pressure is the sum of the partial pressures of the two fluids, so with say 20% butane, you would have the vapour pressure of butane at that temp x 0.2 + vapour pressure of propane x 0.8

Blended refrigerants will all boil together resulting in a variation to the standard boiling point of any gases in the mix. the neat order of boiling suggested simply does not happen, otherwise blended refrigerants would simply not work.

The result is an effect called 'glide' where the various components are all boiling together but at slightly differing levels, and instead of having a fixed saturation (boiling) point they produce a band of saturation, with the approximate centre being the equivalent mixed saturation point.

Differential boiling of the lighter components first does not occur in isolation.

 

[Graham_Wright]

To return to the basic topic! Pressure dependent resistors may be an answer?

 

[cpedw]

To return to the basic topic! Pressure dependent resistors may be an answer?

Do you mean a pressure transducer? If so, that's not going to tell you contents just vapour pressure the same as a pressure gauge. Weight dependent resistors (load cells) might feasibly give an indication of bottle weight hence contents.

Derek