propane tank purging

Thanks. I am still confused. If the tank is purged, why does it need to be filled within 6 months?

I guess I cannot complain about the 15 pound fill at Home Depot or Lowes. It seems this is entirely a rip off. Most people think they are getting a full tank. In any case, both companies will take any tank in exchange. I got rid of my 10 plus year old tanks and replaced them with tanks that were made within the past couple of years. You do need to pay attention. Several times both Lowes and Home Depot have given me tanks that were many years out of date and did not show recertification. I would not have been able to get them filled while traveling. Now that I have all new tanks, I do not exchange but get them refilled.

Jim, when you do an exchange on LP, the 20 lb. tanks are only filled to 15 lbs. in most cases. It used to be 17 lbs. A regular propane filler will probably fill to 20 pounds. The sticker you saw on the shutoff knob should have been removed when it was filled the first time. Any tank that is over 6 months or a year old, whatever the manufacturer indicates, should be purged even though it was vacuumed purged by the manufacturer. This is a precaution the manufacturer takes.

Maybe someone can explain this to me.....

I exchanged a tank at Home Depot and got a new tank. Tank was made by Manchester and filled by Paraco. Well, partially filled anyway. Home Depot and Lowes both exchange tanks that are only filled to 15 pounds.

There was a sticker on the valve handle. I forgot the exact wording but it said the tank should be purged again if it was not refilled within 6 months. ??

I will continue to have future cylinders purged when new even if there is a sticker indicating the tank has been vacuum purged.

One of the reasons is because there is the safety check valve in the outlet of the cylinder valve. It is there to stop the flow of propane when the handwheel is still open and the hose is disconnected. The poppet of the check valve is pushed in by the POL fitting or acme nut fitting when the hose is screwed onto to the cylinder valve. That allows propane to flow in when filling or out when used. There is a spring that pushes it toward the opening to hold it closed when there is no hose attached. The spring also helps guide the poppet to seat correctly. The spring only needs to be strong enough to do both. If the tank is under pressure with propane and there is no hose attached, the pressure will hold the poppet against the seat to stop the flow of propane. When the cylinder has been vacuum purged of all air the check valve poppet is under vacuum, meaning that it is under suction trying to pull it open. As long as the cylinder valve handwheel is shut tight no air can get into the cylinder. If the spring is not strong enough and the handwheel is turned opening the cylinder valve, air can fill the cylinder negating the vacuum purge. There is no way to know if some kid or anyone else has played with the valves on the unsold cylinders on the store shelf.

The second reason I will continue to get cylinders purged when new is because I have purchased 2 - 30 lb cylinders a few months apart that I was told didn't need purging. The first by a senior tech at my local RV store when one of the junior techs asked him because he was unfamiliar with how to purge. I had always got new 20 lb cylinders purged at that location even when purchased for for a grill. I still insisted it be purged and the "brand new" shiny and not a scratch on it but 2 year old cylinder I was purchasing was filled anyway without purging. I went in to the sales counter to complain and there was another senior tech there that had purged them for me before. The person at the sales counter asked him and he said they always purged them. About that time the other senior tech came in and yelling that he told me it didn't need purging. This is the same person that months before set up the weight disributing hitch on by truck. When I got it home which included 10 miles on the interstate I found the ball loose after I unhitched it. Thank God the spring bars held it tight on the hitch. any way I was told by the others if I had any problem to bring it back. I wound if with a cylinder that was full of propane and was making my furnace sputter and pop. I already had 2 other 7 year old 40 lb cylinders in use that the furnace worked flawlessly with.

The third reason is the idiots filling cylinders that supposedly have been properly trained to fill a prepurged cylinder. My fourth 40 lb cylinder was purchased at a Northern Tools store and filled at U-HAUL. Like my 3rd cylinder it had a sticker certifying it was vacuum purged. I wanted it purged with propane anyway and told the filler. All of the guys filling propane there had been recently retrained and certified by Suburban Propane to fill portable cylinders. They had not recently been purging cylinders because their purge rig was no good. The last time I had propane cylinders filled there they told me they were getting new purging equipment. I brought one of my older cylinders and the new no. 4 cylinder I purchased. I told the guy to fill the older cylinder and purge and fill the second and asked if the new gear had arrived to purge cylinders. He said yes and started filling the old cylinder. When finished I took the older tank to put in the truck when I got back he was already filling the new cylinder. I asked him why he didn't purge it. He said he did and showed me he opened the spitter valve before before he connected the hose and started and that had purged the cylinder before he started. So much for retraining. The manager didn't charge me for improperly filling the new cylinder. I was told if there was a problem they would take care of it. Right. Neither place did anything to refill the cylinders because they didn't have any way to safely empty the cylinders and would not buy me new cylinders, to just bring them back when I got them empty and they would refill them free. I was now stuck with 2 unpurged cylinders full of propane that I could not get emptied or refilled properly, the second one of which any vacuum purge it may have had was filled with air before ever having propane put in it. That cylinder also caused my furnace to sputter an pop so there must have been air in the other one when it was filled.

I was later able to get Phillips Energy in Gloucester county, Va, a propane supplier to help out. They had recertified cylinders for me in the past for only $5 each. They are the only propane business I can find within a 45 min drive that will purge or recertify a cylinder. They had a burner on a trailer specifically for burning off contaminated propane from portable cylinders and tanks for rural homes and businesses. I left the cylinders and picked them up a few days later. One of the guys there burned off the propane, put some kind of alcohol in the cylinders to remove water "just in case" because the second cylinder had cold damp air introduced when the spitter valve was opened before filling was started while it was snowing. He also refilled the cylinders. All for less than $40. The cylinders have worked fine and the furnace flawlessly since.

I can't say if the second new cylinder which was only 3 months old would have worked out okay if the filler at U-HAUL would have at least partially filled it before opening the spitter so damp air wouldn't get sucked in before he started, but the first was filled partially before the spitter was opened. Even though it was vacuum purged at the factory it still apparently got air into it some how sitting on the shelf before he ever filled it.

camper19709 wrote:
Yes. My tank was so full of air that the tank would not fill. The vapor vent needed to be opened for an extended time to expel the captured air. This was at a large propane supplier in Arizona that serves RVers.

Air and gaseous propane are both compressible. The purpose of purging any air from the tank isn't to allow the tank to be filled, it's to prevent air from mixing with the propane causing poor burner performance including flame outs. A full tank of un-pressurized air will compress to fit in the 20% of head space left after a proper 80% fill.

F450 wrote:
So I guess that FMCA didn't know what they were talking about when they said that a propane tank should be purged every so often.

If a tank has remained closed to outside air intrusion, there's no needed for periodic purging.

Ron3rd wrote:
......believe it or not, they're even selling "pre-purged" tanks now that supposedly do not have to be purged when you buy them.

As Jesseannie referred to, Worthington and others have pre-purged tanks available. A vacuum is drawn on the tank at the factory to remove the air, and the tanks are shipped still under the vacuum. No additional purging is needed prior to the first fill.

......believe it or not, they're even selling "pre-purged" tanks now that supposedly do not have to be purged when you buy them.

So I guess that FMCA didn't know what they were talking about when they said that a propane tank should be purged every so often.

I just bought 2 new 30 pound Worthington cylinders from Lowes they had a sticker on them that stated they had been vacuum purged at the factory.
Good to fill and go.
Jesseannie