Topping up the up the underslung LPG tank

[tonyidle]

Apparently, some non-return valves are prone to sticking if they close very slowly. I can't remember if it was a specific brand that was susceptible, or even where I heard this. But the gist was that the pump shutting off provided a sufficient shock to fully close the valve.

I agree it can happen but the 80% lock-off valve works only to prevent over-filling and there are two more to prevent anything leaking back out of the tank / filler. Whether or not a pump is in use at least one of them will close.

 

[cmcardle75]

I agree it can happen but the 80% lock-off valve works only to prevent over-filling and there are two more to prevent anything leaking back out of the tank / filler. Whether or not a pump is in use at least one of them will close.

I was just trying to indicate one reason that it is less safe. In my view, I would do it myself, but not do it/recommend it to others.

 

[cmcardle75]

Have you experienced this, because I certainty have not.
As I said in my earlier post " as the level reached 77% you could hear the internal 80% safety shut off closed with a slight bang and every thing went quite", why would I or anybody else then try to continue with the transfer process and leave a propane cylinder for a long period of time, it's job done ?

I haven't experienced it myself. However, I would also say that the refill valves I've experienced have rarely have such a sharp cutoff. Mostly, they gradually reduce. However, it is the non-return valves that were reported as the issue. I do remain sceptical, though, just reporting what I'd heard. After all, the 80% valve will still open again as you burn off gas, so it is the non-return valves that will be stopping your gas leaving the tank.

 

[tonyidle]

There will be a difference between gas in it's liquid form (which means it is compressed and higher pressure) than when in vapour form (lower pressure). It must be noted that gas pressures when air temperatures are cool will be less than once warm. Your cylinder, hoses and pipework need to handle those differences. I'm sure someone will look up the relative pressures.

Gas in your house mains supply, before and after the meter is supplied in vapour form. It is pressurised, just not at the levels needed to be liquid. The same in your motorhome, once it leaves the tank / cylinder to the appliances, where it has effectively "boiled off" within the storage cylinder. So downstream of the onboard tank cylinder all hoses to the cooker, water heater, and external BBQ point only need to handle the lower vapour gas.

Upstream of the cylinder, on it's inlet side, the liquified gas will need more robust couplings, pipes and hoses to handle the liquid, and keep it liquid. If it were to vapourise, the expansion required is substantial, no doubt one of the reasons for the 80% limit.

The adaptor hose and connectors used by the OP was designed by manufacturer for connection of a Calor type external cylinder to the tank inlet. It will have been tested for that purpose i.e. a regulator on the external cylinder to enable transfer of the gas vapour into the empty on board tank. Vapourisation occurs at the external cylinder in this application, and does not repressurise within the onboard storage.

Whilst the OP "got away" with turning the calor external cylinder upside down and was able to transfer the LPG in liquid form, the hose and connectors used were not designed for that pressure and purpose. There must be safety risks with a liquid transfer in this manner, particularly in the absence of controls to keep the gas in liquid form and control temperatures. The OP may be prepared to accept those risks, but comments in this thread should show the practice is at best unwise. The internet will be full of examples of people trying similar methods, notably examples of how to self refill the portable calor type cylinders with LPG, again with hoses and adaptors never intended for that purpose..

The pressure within LPG and its vapour when contained within a vessel or hose are identical. The chemical compositions of both are the same. The temperature is the same (there will no doubt be transient changes in temperature as it is pumped). All this means is that hoses and connectors designed to work with unregulated vapour will work equally well with liquid. They cannot be designed otherwise when they're to be used to transfer a substance that can be in either state.

 

[cmcardle75]

The pressure within LPG and its vapour when contained within a vessel or hose are identical. The chemical compositions of both are the same. The temperature is the same (there will no doubt be transient changes in temperature as it is pumped). All this means is that hoses and connectors designed to work with unregulated vapour will work equally well with liquid. They cannot be designed otherwise when they're to be used to transfer a substance that can be in either state.

However, you do need to use high pressure (HP) hose, which is rated for pressures that constrained propane vapour with a source of liquid propane reaches in reasonable temperatures (17.5 bar is a typical rating by memory, but I might be wrong on the exact figure). A BBQ hose for use after a regulator will often (but not always) be LP hose, which is not rated for that pressure. Don't just go by colour, read the spec on the side.

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[tonyidle]

However, you do need to use high pressure (HP) hose, which is rated for pressures that constrained propane vapour with a source of liquid propane reaches in reasonable temperatures (17.5 bar is a typical rating by memory, but I might be wrong on the exact figure). A BBQ hose for use after a regulator will often (but not always) be LP hose, which is not rated for that pressure. Don't just go by colour, read the spec on the side.

I said "this means is that hoses and connectors designed to work with unregulated vapour will work equally well with liquid". PRVs are set at 25Bar so that is the minimum pressure that hoses and connectors must withstand.

 

[cmcardle75]

I said "this means is that hoses and connectors designed to work with unregulated vapour will work equally well with liquid". PRVs are set at 25Bar so that is the minimum pressure that hoses and connectors must withstand.

I'm not sure it needs to exceed the PRV rating. It is being used to transfer under controlled conditions, which includes knowing the temperature. The PRV on the tank is used to vent gas in a fire to avoid explosions when being consumed in a fire, not to protect against over-pressure under normal operating conditions.

The physics/chemistry will limit the propane pressure under normal temperature conditions, as the pressure is generated from the evaporation of vapour from liquid, which happens on a predictable curve of temperature against pressure.

Rubber hoses don't need such protection against fire, as they will melt before they explode. Metal tanks do, as they will withstand very high pressures as the ambient temperature increases in a fire and the explosion becomes more of a danger than the fuel it contains being released at a lower pressure.

 

[Geo]

Geo, I am genuinely interested in why the Gas exchange In your opinion is so dangerous, if you can explain this I am happy to Listen and learn, if you cannot then that is fine too as you hold such a strong view.

For those who understand no explanation is required.
For those that dont understand no explanation is possible.
Very wise words unfortunately I cant claim them as mine.
Would it change your mind if I said what you are doing and proposing to others is unlawfull.
Thought not!

 

[Googlebot]

Unlawful?

Which law does it break? Can you specify which one?

I am not being an arse, I am genuinely interested as to what legislation this would breach doing it in your own house?

 

[Geo]

Look it up on the LPG suppliers web site HSE web site it is well documented
and your question was truly expected, I have done trying to educate folk that know better.

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[Googlebot]

Well, if it is well documented I can’t find it.

Drum / cylinder handling

www.hse.gov.uk

Was the closest I could get and that doesn’t prohibit it?

 

[Coolcats]

.

For those who understand no explanation is required.
For those that dont understand no explanation is possible.
Very wise words unfortunately I cant claim them as mine.
Would it change your mind if I said what you are doing and proposing to others is unlawfull.
Thought not!

I don't know who you are quoting but it is nonsense as no one is born with knowledge of anything, so once again Geo please explain why it is dangerous as you have not managed to do this yet, as I say I am willing and eager to learn as many others are.

 

[Mr porky]

I’m not sure about having the cylinder in the heat and then having it upside down to drain the bottle but when a new gaslow or equivalent is fitted the fitter used a bottle from the gas barbecue connection to put gas in the tank to test it.

 

[DDJC]

Look it up on the LPG suppliers web site HSE web site it is well documented
and your question was truly expected, I have done trying to educate folk that know better.

I am loath to step into a private fight, but I fall firmly into the category of folk who don't know better, i.e. ignorant of why what has been suggested is as dangerous as you say it is. Not that I have any wish to refill my Gaslow anywhere except at a pump, but I am certainly curious. I know very little about gas, I know it is liquid under pressure, I know what a BLEVE is and I know that it explodes only in a specific range of ratios of gas : air mix. But like most folks, I mostly just put gas into the system, light the hob and I boil the kettle. Easy.

Having spent £500 on a Gaslow system, I am somewhat annoyed to find that the number of autogas outlets is diminishing rapidly, and for that reason, I would like to know what safe and legal options we have when ALL the autogas pumps have gone; ergo my interest in your answers.

When asked a question in my job, I work on the the assumption that they are asking me because they don't know and they think I do. I would never assume that anyone was asking me because they wanted to find fault with my eventual answer or logic.

 

[jessthedog]

Why dosent someone send the photo and attached message to Gaslow and ask them if it is an acceptable and safe way of topping up the tank!
That will settle it, one way or the other.

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[Basildog]

Why dosent someone send the photo and attached message to Gaslow and ask them if it is an acceptable and safe way of topping up the tank!
That will settle it, one way or the other.

Don’t worry I already have
I was going to answer but don’t want to spoil the fun

 

[Kannon Fodda]

Both Gaslow and Gasit make the hoses and adaptors that will allow you to connect the portable Calor type cylinder to the fill inlet of the onboard tank. Both Gaslow and Gasit on their descriptions the hoses are for reserve use, to transfer vapour and that you will not fill liquid with them. Transfer of liquid gas is thus outside of the design parameters of the hoses, beyond what they were intended to do. At best there is some unquantifiable risk by transfering liquid gas. If actually illegal I don't know.

 

[jessthedog]

Don’t worry I already have
I was going to answer but don’t want to spoil the fun ⚠

Come on then, spill the beans!.

 

[cmcardle75]

Unlawful?

Which law does it break? Can you specify which one?

I am not being an arse, I am genuinely interested as to what legislation this would breach doing it in your own house?

It would be unlawful to refill your propulsion LPG tank like this, as you've not paid the correct amount of tax.

 

[Googlebot]

It would be unlawful to refill your propulsion LPG tank like this, as you've not paid the correct amount of tax.

You are right, I hadn’t thought of that.

Still waiting regarding which law though for the domestic use tank.

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[cmcardle75]

You are right, I hadn’t thought of that.

Still waiting regarding which law though for the domestic use tank.

I very much doubt it is illegal in the slightest. However, you need to know what you're doing to do it safely. That's all.

 

[cmcardle75]

You are right, I hadn’t thought of that.

Still waiting regarding which law though for the domestic use tank.

Well, you don't, because red diesel (no road tax) is cheaper than white (with road tax)! However, when in comes to LPG, it is the opposite. Autogas with the road tax is cheaper than Calor, without!

 

[Coolcats]

Don’t worry I already have
I was going to answer but don’t want to spoil the fun ⚠

Oh please, it would be interesting to hear their take on it.