Propane Tank Vacuum Purge

Proper procedure for purging a propane tank with propane vapor (propane gas) and why.

propane cylinder purging

I believe you only have to do use propane vapor (propane gas) 3 times on the smaller DOT cylinders of 100 lbs and less, but I can't find the link.

Looks like I might be wrong. Everything I can find says 5 times. Including regulations from the Utah State Fire Marshall.

Yes boys and girls. Some state regulations require cylinders shipped with air to be purged with propane vapor (propane gas) for the reasons stated in the link above.

I can't make a shortcut to the Utah link, but if you copy paste what I put below into your browser it will pop up in the search. Other state propane regulations may also show up. So regardless of what the maysayers state about being unnecessary state regulations may require purging.

Utah LP-Gas-Basic-Filling-Procedures-Gen-Info-1

Ok, I rechecked the stickers. The sticker doesn't Vacuum Purge it says VACUUM PURGED!

So, should I assume that the tanks have been purged already and are ready to fill?

Purge might be good as long as someone hasn't turned the valve handwheel or opened the spitter screw.

There is a one way built in check valve that doesn't allow propane to flow out unless it is depressed when the acme nut or POL fitting is screwed into the cylinder valve. It is also depressed when the tank is filled.

With the cylinder under vacuum the poppet could open drawing air into the cylinder if the handwheel is turned. Air can also enter the cylinder if the spitter screw is opened.

A propane supplier told me if the cylinder is more than 6 months old he purges them with propane vapor anyways.

Just have it filled and go camping.

time2roll wrote:
Just have it filled and go camping.

Exactly....
That propane cylinder was shipped under a vacuum (vs air pressure)

rhagfo wrote:
Just means that the propane dealer doesn’t need to use propane to purge the air from the tanks. Otherwise they need to put a small amount of propane in the tank then release it to flush any air out of the tank.

Every time I get my tank refilled, they open the overflow (?) valve and fill until propane comes out. No air left !

SDcampowneroperator wrote:
Its a gimmick. Fuel to air ratios fall between the too rich and too lean for combustion, even then there has to be an ignition source in that critical % state in side the container.

It has never happened. Purging is just a gimmick used by suppliers to charge you for something you do not need. Big tanks like 500 gallon tanks are shipped and filled with air at atmospheric pressure. They are not vacummed or purged. The negligable air and oxygen becomes too rich of a mixture to burn,

Propane 101
Ask your local firefighter.


The potential water vapor could be a concern IF filled on 100% humidity day, IF used on much a colder day in which the tank empties to allow the water to boil. Otherwise, water will become and remain liquid until the pressure drops so low as to cause it to boil off or to freeze dry. That would be far below the boiling point of propane at -44.3 f Niether is ever likely or documented. It just cant happen

Talk to your local firefighter. not your propane supplier Its akin to asking to a used car salesman vs a scientist One will tell you its safe , the other truth. both will tell you its safe
Talk to your local fireman!

Ever notice how people who have little or no knowledge of a subject are the most ardent in their opinions? I will take a propane supplier's word over a "firefighter's" word any day concerning propane. Note that a "propane supplier" is not the local UHaul guy or campground employee pumping propane.

I dunno about that, Bobo. I grew up in a fire family, and dad and all his buddies really knew their stuff. They studied and drilled on this stuff all the time. I wouldn't discount their expertise for a second.

Not that good LP guys aren't knowledgeable too, but the average propane monkeys don't seem to be. How many times have you had someone refill your tanks and not even bother wearing gloves or eye protection? They may have standards somehow, but I don't see it in practice, and I don't detect a lot of training or science in what they do.

Old-Biscuit wrote:
New propane cylinders are shipped either with 100# Air pressure OR under a vacuum

Air Pressure........Cylinders need to be 'Vapor Purged' 4 times to remove all air

Vacuum......propane vendor just fills them. NO Purging necessary


Check that 'sticker' again.

Why is some of this stuff so hard for people to understand??
Thanks Old-Biscuit!

theoldwizard1 wrote:

Every time I get my tank refilled, they open the overflow (?) valve and fill until propane comes out. No air left !

That "overflow" valve is actually the "Fixed Liquid Level Gauge". When the escaping vapor turns to escaping liquid the tank or cylinder is filled to the maximum legal 80% of the liquid capacity to allow for expansion.