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Old 05-30-2013, 07:33 PM   #1
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New valve in propane tank - purge air or fill the tank ?

I am going to have the valves replaced in two 100 lb propane tanks. I have read on the internet somewhere that the air needs to be purged from a tank when the new valve is installed or there will be diminished performance from the fresh filling.

My thoughts are: 1) When the tank gets filled, the operator always cracks the bleed valve open until the liquid propane comes out, then the tank is full of liquid.
2) As the liquid propane enters the tank, it will not only displace air (which goes out the bleed valve, and is also producing vapor, which is heavier than air and will also displace air.

So, do I need to be concerned with asking the technician about bleeding the air out at the risk of looking stupid, or do I just get the tanks filled as normal and go with it ?
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Old 05-30-2013, 08:03 PM   #2
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The shop installing the new valves should be able to tell you if the purge is necessary.
The shop that changed my valves , always filled the tanks at the same time .
Remember the only stupid question is the one you don't ask.
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Old 05-30-2013, 08:23 PM   #3
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The biggest problem I have is my fixed income budget.

The shop replacing the valves charges almost 2 bucks a gallon and there is a place not far from there I can buy for a buck and a half a gallon. I am thinking of asking them (after they replace the valves and do the recert stamp on the tanks) if they will price match the other place.

Every bit of money I can save helps.
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Old 05-31-2013, 07:30 AM   #4
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Most distributors put a vacuum pump on the tank for several minutes when a valve is replaced or on the initial fill of the tank. Many times there's moisture in the air remaining in the tank. If it's not removed (by using a vacuum pump) it will condense to liquid form when the cold propane is added. It can then work it's way into the valve and possibly all the way to the regulator. The cold prpoane vapor can cause it to freeze stopping all flow.

Years ago you could just fill the tank to the top forcing out the moisture. Now that we have the OPD valves the tank can only be filled to 80% so you can't purge all the air from the tank. When putting a vacuum on the tank you cause the moisture in the air to boil at room temperature. It's then removed as a gas so it can't mix with the gas or freeze in the tank.
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Old 05-31-2013, 08:04 AM   #5
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Quote:
Originally Posted by mtnmankev View Post
I am going to have the valves replaced in two 100 lb propane tanks. I have read on the internet somewhere that the air needs to be purged from a tank when the new valve is installed or there will be diminished performance from the fresh filling.

My thoughts are: 1) When the tank gets filled, the operator always cracks the bleed valve open until the liquid propane comes out, then the tank is full of liquid.
2) As the liquid propane enters the tank, it will not only displace air (which goes out the bleed valve, and is also producing vapor, which is heavier than air and will also displace air.

So, do I need to be concerned with asking the technician about bleeding the air out at the risk of looking stupid, or do I just get the tanks filled as normal and go with it ?
On the bold, no, that's not true. That bleed valve is attached to a stem fasten to the bottom of the valve that reaches down to the 80% full mark within the tank. So when filling, you'll see liquid appear when the tank is 80% full. Any air in the tank will be trapped in the area above that.

To purge the tank, normally you would put a gallon or so of propane in it, then turn it upside down and open the valve - releasing that gallon of propane as well as any air.

I've never seen a tank pumped down using vacuum, but it seems like that would work fine as well. Not sure how many propane stations are equipped with those though - or the potential for trouble pumping propane vapors through a vacuum pump?

Assuming you're on a budget, have the valves replaced when the tanks have emptied. Then take them to have them purged (as described above) at the inexpensive propane supplier. -Al
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Old 05-31-2013, 09:54 AM   #6
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Quote:
Originally Posted by Hikerdogs View Post
Most distributors put a vacuum pump on the tank for several minutes when a valve is replaced or on the initial fill of the tank. Many times there's moisture in the air remaining in the tank. If it's not removed (by using a vacuum pump) it will condense to liquid form when the cold propane is added. It can then work it's way into the valve and possibly all the way to the regulator. The cold prpoane vapor can cause it to freeze stopping all flow.

Years ago you could just fill the tank to the top forcing out the moisture. Now that we have the OPD valves the tank can only be filled to 80% so you can't purge all the air from the tank. When putting a vacuum on the tank you cause the moisture in the air to boil at room temperature. It's then removed as a gas so it can't mix with the gas or freeze in the tank.
A frozen regulator is a real pain in the keester.
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Old 05-31-2013, 12:58 PM   #7
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When the law was changed and the portable tanks had to go to 80% valve, we changed all the tank valves at our lot. We changed on a non rainy, non cloudy day. We removed the old valve and immediately installed the new valve. We had no problems with the tanks.
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Old 05-31-2013, 03:59 PM   #8
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when they purge tanks here they open the release valve and add gas then after a minute or so they close it and the air is mostly gas then ....jeff
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Old 05-31-2013, 04:08 PM   #9
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Propane is heavier than air and under pressure so once the tank is filled when the
main valve is opened for a few seconds the small amount of air is released.
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Old 05-31-2013, 04:43 PM   #10
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During the initial fill, leave bleed closed, pump 1 gallon, stop pumping, open the bleed for 30 seconds, close the bleed. Repeat 3 times, then fill normally.

Former propane pumper.......
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