Emptying LPG Tank

[richard_ha]

I need to empty my tank so that I can remove the multivalve.

What is the safest way to do so? I imagine there's going to be at least 5l of LPG left in the bottom of the tank?

[bxman]

If you have run it till it runs out there will be nothing more than a tank of vapor left which will vent to atmosphere very quickly. best done out in the open without any open flames or naked lights about {try inserting a prohibited word good old nanny state}

[richard_ha]

Thing if it my pick up is in the wrong place I could potentially have up to 10l of liquid in there.

Do I just start unscrewing the multi valve or should I disconnect the feed and put 12v across the solenoid?

[mat_fenwick]

Whatever you do, don't make or break any connections near where the LPG is being released… What I would be tempted to do is disconnect the outlet pipe (after running on gas as much as you can) and connect 12V across the solenoid, in an exposed place whilst not smoking I would first wait and see if anyone more knowledgeable can add their wisdom to this though.

We had a bit of a dilemma a few months ago - failed solenoid in the engine bay, no manual shut off on the multivalves and even though I disconnected the solenoids on the tanks it appeared they were stuck open (and we'd just filled the tanks…) So, no way to run on gas to empty the tanks, and no way to isolate the gas supply from the solenoid I wanted to replace. Had to wait for a windy day and vent off 60 odd litres.

[demonicwillow]

Well when I did mine, I carefully released the gauge sender assembly, slackened the 4 bolts but didnt remove, eased out the sender and let it gently vent off, made sure that no one was around, no nakked flames, ciggies or anything that would make a spark, but if anyone did walk past I could just tighten the sender back down to stop venting if there was an issue.

If you go down the 12v across the solenoid route, make sure the solenoid is properly connected to a long lead and keep the power source a good distance away to prevent any possible sparking from igniting the vented vapour, just remember that if there is a few ltrs in there, you will get a fast liquid discharge which will then vaporise, I personally would be more inclined to allow vapour venting carefully rather than quick liquid discharge, but each to their own method.

[bxman]

IMO If you drive around in a economy mode the feed from the tank will supply sufficient amount of vapor to run the car and so exhaust the tank even if the pickup tube is well clear of the liquid that may be left in the bottom of the tank.
No doubt rossko will be along in second or two to put me right if he considers that I am mistaken.

[rossko]

Nah, I'm with you on that
You can get enough vapour up a 6mm pipe for the engine to idle (not so sure about driving around) and that's undoubtedly the safest way to 'flare it off'.

[jayc]

I've vented a few tanks before. As has been said if using the solenoid be careful of the power connections, choose a windy day, don't vent directly above a drain and you should be fine.

You can get enough vapour through a 8mm hose to run a 5.7L engine at around 50% power though. I recently troubleshooted a boat which had been converted from normal 4 hole tank to using red 19KG bottles. It was down on power but had still been used all season. Turns out instead of using 18KG FLT's they where using 19KG vapour bottles. I suggested turning them upside down, instant power boost! Still far from ideal and I suspect the valves where shot due to excessive lean running.

[demonicwillow]

Where were the bottles stored ??

[evautos]

Hello all,
I normally drive the vehicle until it changes back to petrol because of pressure drop (or loses power if mixer system), if the system is working ok. Then I run the engine with a throttle depressor holding revs at around 2500rpm with the vehicle stationary(keeping an eye on temperatures etc), until it cuts out or changes back to petrol & then leave it idling, until it cuts out, changes back to petrol. This usually takes about half a day to do on the average 70 ltr or so tank, but when you then remove the multivalve , there is hardly any vapour remaining. My problem is that there are several houses around me nearby, so I've got to be carefull about venting to atmosphere, remembering that liquid lpg expands about 250 times when it vaporises, being combustible between 2-10 % in air, with 1 ltr yielding approximately 12500 ltrs of flammable mixture(sorry to those approved installers reading this that already know these figures).
When there is a problem where the system won't run the engine, such as when liquid pumps pack up, I usually connect the outlet to an empty lpg cylinder & power the solenoid, until the pressures equalise & lpg stops flowing. I then use my space heater in the workshop to burn off the lpg in the recovered cylinder, until it runs out & start over again. I usually use two cylinders so that one is filling whilst the other is being burn't off & I also have the vehicle outside in the yard, whilst the burner is operating in the workshop obviously.
I have been told by a friend(an installer) that he once removed a multivalve with the contents in the tank & the flowing vapour/liquid froze over & sealed the hole in the tank, then he fitted another valve( i've never tried it & think it may not be possible to do), but there must have been a lot of vapour hanging around
Hope this helps, regards, Andrew

[jayc]

Where were the bottles stored ??

Just at the stern of the boat. It was a ski boat so they just strapped to the gunnels. Oh did I mention the local hydraulic shop sold them the fittings and said it was ok to use orange hose and jubilee clips on the high pressure hose!

Luckily it's back to a 4 hole tank now and correct hose/fittings.

I once vented a very old 110L 4 hole tank that was nearly full to replace the dip tube as it had broke off. It had a manual supply lock off so on a windy but cold winter day i started venting it. It took a good 45 mins or so then pretty much stopped. The hole tank was incased in ice due the vaporisation of the LPG. I removed the supply fitting and thought I'd roll the tank over to see if the snapped off dip tube could be fished out. Turn's out the tank wasn't empty but the tank temp had dropped enough to keep the LPG liquid. On roling over the LPG flowed out rather quickly, hit the ground and some of my tools which must have been considerably warmer than the ground and instantly vaporised. Did I jump, hell yes!!