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Anyone know about LPG?
ChrisW - 27/12/17 at 07:31 PM

Or more specifically, pumping it from one tank to another?

Scenario is this: I bought an LPG-powered Jeep. I wanted a cheap runabout that could pull a decent sized trailer and deal with the odd bit of mild off-roading (mainly dragging said trailer through a field) and it fits the bill nicely. OK it only does 15-ish mpg but with LPG being about half the price of petrol I get the equivalent cost of about 30mpg whilst still being able to drive about in a 4.7 v8.

What is getting on my nerves however is having to fill it up. It only has a 70l tank which, once you take into account only being able to fill it to 80% (standard practice to leave expansion room) means only 55l of LPG available and therefore about 150-160 miles between trips to the only LPG supplier around which just happens to be completely the opposite end of town to where I live.

Clearly if I had some way of buying in bulk and filling the car up myself life would be a lot easier. The gas is the same stuff as used for heating, and there is a process with HMRC (Google C&E930B if you are interested) for declaring that you have used heating gas as road fuel and paying the difference in duty, the issue is one of getting the LPG from a bulk tank into the car.

I have managed to acquire a 1000l tank with a bottom outlet (required to get the contents out as liquid) I now just need some method of pumping the gas from there into the car. Has anyone attempted something like this before?

As I understand it, I need a positive displacement pump. The commercial installations use a gear type pump but 'proper' LPG ones (eg from Smith pumps in the US) are expensive. I have also heard of DIY'ers using sliding vane type although apparently there is some issue of cavitation at the tips of the vanes causing the liquid to turn to gas and massively reducing the efficiency of the pump (I don't profess to understand the physics behind that).

Would a gear type hydraulic pump do the job? If so, will the LPG act as a lubricant or am I going to either have to make some other arrangements to lubricate or just accept that the pump will die over a period of time?

What about a car air-con pump? These are usually piston type pumps with a non-return valve at each end. I hesitate here as I was taught when I did my F-gas certificate that allowing liquid in to AC pumps was the most common way of killing them but I have no idea why that is. My only guess is that it is something to do with the non-return valves.

Anyone got any experiences or advice they can offer?

Chris

BenB - 27/12/17 at 07:52 PM

Can't help with the original question but is there such a thing as "red" LPG? IE what's to stop people using heating LPG for cars? Or do they just assume the number of LPG cars is quite low and the number of people who have the knowledge to transfer LPG without flame-throwering themselves even less so???

luke2152 - 27/12/17 at 07:54 PM

Loads of forklifts run on LPG and I assume they get filled on site so I guess smallish bulk equipment must be available. Also some of the small LPG filling stations look like they have pretty basic equipment.

Couldn't you just connect the tanks without a pump and have a bit more pressure in the external tank to force it to the car tank. Or pressurise it with welding gas. I'm sure the pressure in the car tank is pretty low (2bar rings a bell).

I don't think LPG is taxed at all so not sure buying heating gas will be any cheaper although I guess buying in bulk is.

ChrisW - 27/12/17 at 09:25 PM

quote:
Originally posted by BenB
Can't help with the original question but is there such a thing as "red" LPG? IE what's to stop people using heating LPG for cars? Or do they just assume the number of LPG cars is quite low and the number of people who have the knowledge to transfer LPG without flame-throwering themselves even less so???


Answer was in my original post.

quote:
Originally posted by ChrisW
The gas is the same stuff as used for heating, and there is a process with HMRC (Google C&E930B if you are interested) for declaring that you have used heating gas as road fuel and paying the difference in duty, the issue is one of getting the LPG from a bulk tank into the car.


So yes, all heating LPG is 'red', but unlike red diesel you can declare your usage in order to be legit with HMRC, and of course there is no way to dip an LPG tank.

quote:
Originally posted by luke2152
Loads of forklifts run on LPG and I assume they get filled on site so I guess smallish bulk equipment must be available. Also some of the small LPG filling stations look like they have pretty basic equipment.


I have not seen or heard of a DIY refilling machine for fork lifts. If such a thing exists I would certainly be interested to hear about it!

quote:
Originally posted by luke2152
Couldn't you just connect the tanks without a pump and have a bit more pressure in the external tank to force it to the car tank. Or pressurise it with welding gas. I'm sure the pressure in the car tank is pretty low (2bar rings a bell).


I believe you could, but as the volume in the bulk tank decreases so does the maximum you could fill the car. Also the time taken to transfer will increase. Pressure in an LPG tank is roughly 100psi (about 7 bar) I believe. This is based on the vapour pressure and varies with temperature.

quote:
Originally posted by luke2152
I don't think LPG is taxed at all so not sure buying heating gas will be any cheaper although I guess buying in bulk is.


Price for heating LPG is about 32p/litre, then you have to pay 10p/litre duty on top (I believe) so should save me about a third on the local place (currently 62.9p/litre).

[Edited on 27/12/2017 by ChrisW]

rash12 - 27/12/17 at 09:38 PM



might not be for you but i used to get lpg from an upturned 47kg cyl using one of these made your arm ache i suppose you could motorise it mine was on a hand lever

[Edited on 27/12/17 by rash12]

[Edited on 27/12/17 by rash12]

ChrisW - 27/12/17 at 09:51 PM

That looks like the one on the DIY-LPG site here.

Tinley Tech sell them pre-made here but not sure I want to hand pump it each time. You are right though I could potentially motorise it.

I was thinking of buying something like this: eBay Item. OK it will be slow (4 litres per minute) but I can just hook it up and leave it running for ~15 mins. It is a gear type pump like the 'proper' ones. Has anyone got any comments on whether this will work or not?

Chris

rash12 - 27/12/17 at 10:09 PM

thats where i got the plans from worked well used it for a couple of years

02GF74 - 27/12/17 at 10:30 PM

Is fitting a larger or second lpg tank not an option?

ChrisW - 27/12/17 at 11:22 PM

quote:
Originally posted by 02GF74
Is fitting a larger or second lpg tank not an option?


It's possible, but I would lose even more boot space, even doubling the tank size (which would be a push) would only half the number of trips to fill up, and would mean I had to throw the idea of saving money on the gas out of the window.

llionellis - 28/12/17 at 11:02 AM

I have never pumped LPG, but have been involved with liquid transfer many times over the years. My first point of call for a positive displacement pump
with known reliability would be an air operated diaphragm pump and my choice of manufacturer would be Blagdon. They are not cheap and would probably eat into the cost saving between LPG and other fuels.

trextr7monkey - 28/12/17 at 02:16 PM

Once read an article in some Cumbria mag about an Estate agent who worked around Coniston running a massive engined Range Rover and he had a tank at home to top it up so it can be done. We use lpg for heating but tank belongs to Shell. If you are buying bulk could you not get a free tank and pump from a supplier?
Atb
Mike

mark chandler - 28/12/17 at 05:50 PM

I used to invert 47kg cylinders and pump them into my Range Rover, less than 25p per litre, used to go through 4 a month.

I started off with a vane type pump, slow and fell apart so moved onto a quality diapham pump that was pretty quick although cost maybe £250 at the time, it was a quality bit of kit.

Looked like this. Lpg Transfer Pump
The problem is LPG rotting the seals.

[Edited on 28/12/17 by mark chandler]

Angel Acevedo - 28/12/17 at 10:53 PM

Back in the days working as an interpreter I remember a Video about an accident involving propane and Liquid transfer in Ghent, W.Va.
Shouldn“t be that hard to google.
Not to discourage you, but to make sure you review and heed all safety procedures before attempting such transfers.

Angel Acevedo - 28/12/17 at 10:55 PM

Found the page and video of the accident recap...
http://www.csb.gov/csb-safety-recommendations-from-ghent-west-virginia-propane-explosion-largely-adopted-effecting-life-saving-change/
Link to video on page...

coozer - 29/12/17 at 10:47 AM

A few of the rdcs I go with my truck have a big tank and the forklift drivers fill the cylinders from it. Not sure how it works but next time I'm there I'll take a picture of the pump arrangement.

Might be while yet like cause I'm sunning mesell in Tenerife atm...

sebastiaan - 29/12/17 at 12:15 PM

Having worked with LPG professionally for years (decade and a half) I only have one advice: don't do what you are planning. Transferring LPG from one tank to another regularly, safely and reliably isn't a DIY proposition. Having a modified 1000L tank at home also isn't. Just think what will happen if one of your fittings fail.

Sorry to be the bearer of bad news. I'm usually all for doing stuff yourself, but this is just a bad idea and possibly lethal...

ChrisW - 3/1/18 at 05:45 PM

First off, thanks for the comments everyone.

quote:
Originally posted by mark chandler
I used to invert 47kg cylinders and pump them into my Range Rover, less than 25p per litre, used to go through 4 a month.


I'm going to give that a shot first to prove that my pump set up works and, if all successful, will look at getting the bulk tank filled up. Picked up the correct hose today to connect to a 47kg cylinder.

quote:
Originally posted by mark chandler
I started off with a vane type pump, slow and fell apart so moved onto a quality diapham pump that was pretty quick although cost maybe £250 at the time, it was a quality bit of kit.


I have heard that the vane type pumps work ok as long as the liquid keeps flowing at reasonable speed to carry the heat away. Not heard of anyone using a diaphragm pump up to now but you are right, that one you linked on eBay certainly is that.

quote:
Originally posted by coozer
A few of the rdcs I go with my truck have a big tank and the forklift drivers fill the cylinders from it. Not sure how it works but next time I'm there I'll take a picture of the pump arrangement.


I believe this is a fairly common thing to do. Also a mate who does hot air ballooning says that it is common for pilots to refill their own tanks. I have not managed to find a rig for sale yet though or even a picture of one. My only source of reference at the moment is the local LPG retailer (an independent shop as opposed to a filling station). They have a 1000l tank with Smith's pump feeding a pressure relief valve that feeds back to the tank. I had a look today and the valve is set to 75psi which I assume is relative to tank pressure.

quote:
Originally posted by sebastiaan
Having worked with LPG professionally for years (decade and a half) I only have one advice: don't do what you are planning. Transferring LPG from one tank to another regularly, safely and reliably isn't a DIY proposition. Having a modified 1000L tank at home also isn't. Just think what will happen if one of your fittings fail.


I appreciate your concerns, but on the other hand I am confident that I can come up with something that is safe. The rig will be on a farm in the middle of nowhere, not in an enclosed back garden or with people in close proximity, so if there was a problem it will only be myself in trouble.

The tank already has a bottom outlet, it will not need to be modified. I intend to fit a ball valve directly to the tank with some kind of remote lever to ensure that I can turn it off without having to get too close in the event that something nasty did happen. Yes a fitting could fail, but as long as the isolation tap is a quality part and I switch it off when not in use I do not see any more of a risk than at the local filling place which, incidentally, is amongst a busy industrial estate.

I understand that you might not want to give advise, but surely it would be better to help me find a suitable method for doing this than withholding information that would help me avoid making safety mistakes?

So my plan at this point, unless anyone can tell me otherwise, is to buy that gear-type hydraulic pump from eBay. As above, I am aware that it will be slow, but it is priced such that it is not the end of the world if it doesn't work. My concerns are whether the LPG will provide sufficient lubrication and whether the viscosity of the liquid will be too low for the pump to work effectively. The manufacturer states that the pump is suitable for 'Fuels' and 'Petroleum derivatives' and only states a maximum viscosity so I am keeping my fingers crossed that it will work. I have emailed them asking specifically if the pump will work with LPG but am not holding out much hope of a reply.

I will use a pressure valve that vents back to the tank set at 75psi just like the local filling station. I will probably also put an inline filter too just to make sure I am not sucking any debris into the pump.

I will try it going from an 'orange' cylinder first, probably a 19kg one as that should be less than the size of my car tank and therefore no chance of overfilling. If that works and seems to be effective and reliable I will probably try pumping a couple of 47kg cylinders into my bulk tank and then filling from there before I go ahead and get the tank filled right up. 1000 litres is a lot of gas to waste if I can't get it to work!

Anyone care to point out any mistakes or other considerations before I go ahead?

Mr Whippy - 4/1/18 at 12:38 PM

I wonder what your house insurance would say if you blew up the place...?

Sure in theory all this is very simple, in concept but I'm sure there is very good reason these things tend to be regulated. I too am looking at LPG for my Landy but will not be making my own filling station at home.






[Edited on 4/1/18 by Mr Whippy]

ChrisW - 4/1/18 at 01:02 PM

quote:
Originally posted by ChrisW
The rig will be on a farm in the middle of nowhere, not in an enclosed back garden or with people in close proximity


As above, will be nowhere near my house, or anyone else's for that matter. If anything was to go wrong there would be very limited fall out, it would certainly not be an issue for house insurance to sort out.

Short of a fitting failing as Sebastiaan mentions, the impact of which I feel can be significantly mitigated by making sure there is a remotely accessible emergency shut off valve right on the tank, I really do not see a much of an increased risk over having a domestic LPG tank in the garden to run central heating. The tank itself is, after all, manufactured to be safe for storing LPG.

Mr Whippy - 4/1/18 at 01:18 PM

yeah I use to have a LPG tank in the garden too, can't say I was ever trying to connect my car to it though. These things kind of escalate rather quickly if they go wrong. 1000ltrs, that's a lot of gas to go bang if it did, mushroom cloud kind of scale, crater in the ground...

I'm not saying don't do it, just do it very very very carefully. I'd be most concerned if the regulator or valve failed and the full force and volume of the gas in the tank tried to get out. Isn't it like 300psi normally in a tank, more in hot weather? you ain't plugging that with your finger. Tbh I shudder when I see some of the contraptions people make on the web though.

Pity the Jeep has such a huge engine, probably produces very little power for it's size

[Edited on 4/1/18 by Mr Whippy]

Oddified - 5/1/18 at 11:35 PM

Whilst i run my van on lpg, i don't have a home filling set-up. I do know a few people that do/have though, and none reported any issues what so ever. The only thing some said was if the big tank is being filled for domestic use (cheaper), they quite often check for a bottom take off pipe/indications someone using it to fill a vehicle. Of course that wouldn't be so easy to check if someone had a top fitting with a dip tube..lol. I never asked them about the transfer/pump so i can't help on that one but reading above it looks like you've done a bit research, crack on

Ian

ChrisW - 8/1/18 at 10:35 AM

quote:
Originally posted by Oddified
The only thing some said was if the big tank is being filled for domestic use (cheaper), they quite often check for a bottom take off pipe/indications someone using it to fill a vehicle.


Thanks Ian. Quite happy to tell them that the gas will be for filling vehicles; it is perfectly legal to do so. You can either buy the gas with the road tax pre-paid or buy it as heating gas and declare the usage to HMRC afterwards using the form I reference in the first post.

Either way I believe it adds about 10p/litre to the gas price so roughly 40p/litre total compared with the best local price of 63p/litre that is still a good saving.

The maths for anyone thinking of something similar: I get about 160 miles of town driving from 50 litres of gas. That is 14.5mpg. This is all rough of course because it does a bit better on a run (not generally what it gets used for) or a bit worse if I have a trailer on the back (fairly common) but at least it gives a ball park.

That 50 litres costs me £31.50 at the local place. With petrol at £1.20/litre roughly that's equivalent cost to about 5.7 gallons of petrol, therefore cost wise the equivalent is about 28mpg. Not too bad for what it is.

The same 50 litres from my bulk tank should work out around £20 with the duty paid, equivalent cost to about 3.7 gallons of petrol and therefore pushing my pseudo-mpg to 43mpg. I would be very happy with that for a v8 4x4!

Plus in my case I would save about a gallon (of gas) on say 50% of fills as I won't have to make a special trip to the other side of town where the filling station is.

Brief project update: I have ordered the hydraulic gear pump from eBay as mentioned above and have a hose with the right connector on it to go to connect to an orange cylinder. I need to get hold of one to connect to the car, I think tinleytech stock them, just need to work out which one I need. I also need to order up a 3-phase contactor and rig that up in some kind of enclosure to make it safe.

I can then do some tests to see whether the pump is effective at moving gas between a cylinder and the car. I will use my air con 'charging' scales to monitor the weight of the full cylinder to make sure I don't overfill the car tank. They are designed for the purpose of weighing cylinders of refrigerant whilst charging AC systems so should be perfect for the job.

Will report back!

Chris

Mr Whippy - 8/1/18 at 12:59 PM

you seem to be mixing fluids/gasses in different items are you sure the material in the seals etc are all compatible?, propane in ac or hydraulic equipment. Another thought is the effects of cold, O-rings for hydraulics are unlikely to be happy if they are chilled.

might be worth checking....

chillis - 8/1/18 at 01:21 PM

I believe you need a licence for filling vehicles with LPG. The LGP 'petrol' station will have one issued by the local fire brigade.
We used to have one for LPG when we ran LPG engines on the test bed. As for transferring from one tank to another its a real headache. You need to ensure the pressure in the bulk tank is greater than the vehicle tank and by some margin or you'll transfer very little and the pressure changes depending on the temperature. Also the bulk tank will be considered a pressure vessel so you made need regular certification. Can you not fit a bigger vehicle tank to reduce the trips to the filling station?

ChrisW - 8/1/18 at 04:24 PM

quote:
Originally posted by Mr Whippy
you seem to be mixing fluids/gasses in different items are you sure the material in the seals etc are all compatible?, propane in ac or hydraulic equipment. Another thought is the effects of cold, O-rings for hydraulics are unlikely to be happy if they are chilled.


The AC scales are just that.... weighing scales. They won't have any contact with the gas itself. They just allow you to tare a cylinder weight and then don't auto time out so you can accurately meter an amount of refrigerant gas (by weight) into an AC system.

Propane weighs (give or take) 0.5kg per litre so the first time I do it I will make sure the Jeep is empty (which means at least a 50 litre fill) and then fill it until the cylinder weighs 20kg less than the start weight. That way I know I will be well within tolerances.

The only hydraulic component I am using is the pump, which is a gear type. As far as I know these use the metal casing against the gear teeth to seal so there should be nothing to perish. The manufacturer does not mention LPG specifically but does say that the pumps are suitable for 'Oil, fuel and gasoline' so I am keeping my fingers crossed.

At the end of the day, as long as I keep the tank and fill valves closed when not in use, even if the pump seal was to fail the worst case scenario is that next time I come to use it it won't work.

Chris

ChrisW - 8/1/18 at 04:24 PM

quote:
Originally posted by chillis
I believe you need a licence for filling vehicles with LPG. The LGP 'petrol' station will have one issued by the local fire brigade.


As far as I am aware this only applies to commercial use, the same as for petrol.

daviep - 8/1/18 at 05:03 PM

FYI, gear pump will have a rubber seal on the driveshaft and also the end plates will be sealed using rubber seals. Should you need to reseal then kits are usually available in Viton which is compatible with LPG.

How will you drive the pump?

Very interests in the outcome of this.

Regards
Davies

ChrisW - 8/1/18 at 06:10 PM

quote:
Originally posted by daviep
FYI, gear pump will have a rubber seal on the driveshaft and also the end plates will be sealed using rubber seals. Should you need to reseal then kits are usually available in Viton which is compatible with LPG.

How will you drive the pump?


Thanks for the info. The manufacturer doesn't state the material used for the seals just that they are 'compatible with the pumped fluid'.

Pump is electrically powered, 3 phase. I have ordered a suitable contactor today to control it and will wire it up with a momentary switch.

Chris

ChrisW - 12/1/18 at 11:58 AM

Update: got all the big parts here. Need a trip to Screwfix to get some jubilee clips and to knock something up to safely activate the contactor at a safe distance from where gas has the potential to escape.

lpg pump bits
lpg pump bits

Have also got a 19kg orange cylinder to use as my first test. Actually more expensive per litre than buying 'real' LPG but it means I can try the rig out without loosing too much money if it doesn't work. See previous posts for the reason why I have selected 19kg as the first trial.

Only problem now is I have a full tank of gas in the car so it will be a couple of days before I can try this all out. If you see a mushroom cloud over a North Buckinghamshire farm you will know why!

Chris

gremlin1234 - 12/1/18 at 12:32 PM

quote:
Originally posted by ChrisW
Need a trip to Screwfix to get some jubilee clips
I've seen lots of things saying not to use jubilee clips on fuel hoses since they tend not to clamp evenly all round

ChrisW - 12/1/18 at 12:52 PM

quote:
Originally posted by gremlin1234
quote:
Originally posted by ChrisW
Need a trip to Screwfix to get some jubilee clips
I've seen lots of things saying not to use jubilee clips on fuel hoses since they tend not to clamp evenly all round


Interesting, thanks. I actually have the tool for O-clips. Perhaps better to use those instead.

Mr Whippy - 12/1/18 at 01:01 PM

yeah...he's still alive

ChrisW - 13/1/18 at 06:34 PM

Ok, so for anyone following along at home I have had some success (I think) with this tonight.

First problem I came across was it appeared the pump was not gas tight. I took it apart to find out why (I figured I had nothing to loose) and it seems the rear seal was not seated correctly. If you are interested, here is what it looks like inside.

LPG rig test 3
LPG rig test 3

I cleaned everything out, wiped out the remnants of hydraulic oil, and put it all back together. All seemed good from both a sniff test (no gas smell) and ear test (can't hear any hissing). Next time I go up to the yard I will take some fairy liquid and double check that there are no weeps from anywhere.

It is worth saying that I had the pump on about 10m of cable so I could stand well back and activate it just in case anything bad happened. The down side of this was I was I could not hear if anything was going wrong, any gas escaping, etc whilst operating the pump.

So anyway, I hooked everything up but didn't connect to the car, and tested running the pump to see if I could get it to prime. It seems there is some kind of stop valve mechanism in the propane tank fitting that I managed to activate the first time I tried, I think because I was being very cautious about opening all the valves at once and probably managed to create a vacuum somewhere. The second time I just opened all but the valve on the car filler end, ran the pump for a few seconds and hey presto I had liquid when I cracked open the valve at the car filler end.

LPG rig test 2
LPG rig test 2

Then hooked it up to the car and weighed the cylinder so I had a starting position. Ran the pump for a few seconds, went over and checked for any signs of leaks, few more seconds, re-check, etc. Did that until I had 30 seconds of pump run time. Checked the cylinder and the weight had dropped indicating transfer of gas. Started running for longer bursts. First 10 seconds at a time, then 20s, then 30s, then eventually a minute at a time checking cylinder weight between each run.

Should also say at this point the car was not empty so I wasn't able to say with accuracy how much space was in the tank. As I have no pressure relief at the moment it was important that I did not get to the limit of the car tank's fill valve. I took a conservative estimate of the gas used since the last fill (based on miles) and halved that to set a max I was going to attempt to fill today.

LPG rig test 1
LPG rig test 1

Sorry the pic is a bit dark.

Anyway, upshot of all of this was that after 6 minutes of total pump run time the propane tank was 6.5kg lighter than when I started indicating 13 litres of gas had been transferred. That is a pretty poor flow rate, about half what the manufacturer claims. That might be because the flow rate is for hydraulic oil which is far more viscous, because the pump is old and the tolerances in the housing are not what they used to be, or because that 6 minutes was made up of short duration pulses. Who knows, but it will do for now.

So there we go: yes, it is possible to DIY fill from a cylinder without spending thousands or going up in a mushroom cloud.

Next step is to run the car completely out of gas and attempt to pump the rest of the orange cylinder in.

After that, hook up some kind of pressure relief so that I can't overfill the car tank. I have not been able to find any data about how much pressure the tank stop valve can take but the relief valve at my local (retail) filling station is set to 75psi so I guess I use that as a guide, perhaps start at 50psi and turn it up from there.

After that, get some bigger cylinders and try to pump into the bulk tank so I can prove that filling from the bulk tank into the car works without having to invest a few hundred in a full fill.

(Edit to fix spelling mistake)

[Edited on 13/1/2018 by ChrisW]

sebastiaan - 13/1/18 at 07:15 PM

Right, you lived to tell the tale. As you are going to do this anyway (bad idea) and asked for tips instead of silence:

1) use hydraulic hose. Anything you use needs to be rated to at least 50-100 bar or thereabouts (I'm not talking legislation/rules here, just experience and common sense) Hydraulic hose works and is cheapish.
2) the pump will be cavitating at the inlet with that thin supply line and the valve(s?) in between. This will cause the low flow and pump wear. Low flow is also caused by the out-of-spec viscosity of LPG. Being much thinner than the design fluids, the pump will leak more internally. The low flow problems will get worse on lung runs if the pump starts to warm up. Once/if the pump gets to a temperature sufficiently high enough above the tank temperature, there will not be liquid at the pump inlet anymore (the gas will have evaporated) and the pump wont pump anything anymore. Best solution: put the pump inside the tank submerged. Next best option: heat the tank (slowly and carefully, a heat mat on a thermostat will do, but you need a lot of heat for a 1000L tank. Next next best: fit bigger lines upstream of the pump to lower the pressure drop over them. If you will or will not have problems depends on how much the pump is cooled by the fuel flow and the pump efficiency. If you are lucky, the pump will stay cold enough to function. Just dont be surprised if this happens at some point.
3) Safety: you need a pressure relief on all parts of the system, that can be "locked out" (i.e. closed at both ends). Ideally a shut off that will allow backflow into the tank, but not out of it. This is also how the automotive LPG lockoffs work.
4) Safety: get, use and hardwire in a gas dectector that shuts off everything when it senses gas. Yes, this means there needs to be an electrical cut off at the main tank as well.
5) Safety: draw up a working procedure around safety and checks and FOLLOW IT RIGOUROUSLY and ALWAYS. Human error will get you killed.
6) Safety: install a dry break coupling in the fuel hose to the car. See also #5. Yes, people drive away from the pump with the hose still connected. Often...

That should get you part of the way there, should you still really want to. Good luck.