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Old 05-16-2022, 08:34 AM   #1
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Overpressure on refilled propane tank

Had my tanks refilled a week ago - one was empty, the other one just needed to be topped off. Shut the trailer down properly and put it into indoor storage immediately after.

Pulled the trailer out to work on the storage space, leaving the trailer nose-first into the Illinois sun. After a few hours, my buddy noticed a propane smell coming from the nose of the trailer. Sure enough, the flies noticed it too, and had started to buzz all over the tanks (flies are a sure sign you've got a leak, they LOVE mercaptan - the stuff that gets added to propane to give it that smell - also present in rotting meat, veg, and poop).

I pulled both tanks off the trailer, and set them in the shade, apart from one another. The flies preferred one tank/ignoring the other so I had my suspect. Mixed up a little soapy water to spray over the tank valving, and - sure enough - the overpressure valve was leaking a little gas. Putting the tank in the sun gave it just enough heat to cause the gas to expand (as propane expands mightily)... which was J U S T enough to overcome the overpressure valve spring.

Hooked the tank up and ran some propane appliances for a while - taking enough off the tank to reduce the volume required. Tested again with my soapy water mixture to find the overpressure valve had reseated.

phew. Felt like I had dodged a bullet.

Well, I know which tank to make my primary/first one for a while. I guess the moral of the story is to be aware of your tank levels after having them refilled!
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Old 05-16-2022, 08:51 AM   #2
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Follow the Science. Gases expand in heat, contract in cool. Looks as if the tank is working as designed???
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Old 05-16-2022, 08:57 AM   #3
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Did you perhaps watch how they filled the cylinders? The reason I ask, depending on how they refilled them and verified they were full, could be indicative to if the cylinder may have a problem with the OPD. Did you transport the cylinders to/from the refill place on their sides by any chance?

I have reasons for asking these questions.

Thanks
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Old 05-16-2022, 11:32 AM   #4
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Yes, Brother Les, tank (and overpressure valve) working properly. Tractor Supply might have just been a little enthusiastic in adding propane to that one.

Hey, WMTire - Tanks were on the rig vertically, all the way to the propane resupply/ I pulled them off and handled vertically, the entire time. Filled with a giant tank and regulator setup, manually (I didn't see the TSC worker preset a PSI or weight). Then right back on the rig, and properly hooked right back up.

Tanks are new-ish from last year delivery of the Roo. I'm not saying anything was wrong with the tanks or how they were handled, I'm suggesting TSC simply put a little more propane in there than the tank should have received, above the 80% rule.
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Old 05-16-2022, 12:01 PM   #5
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Originally Posted by Rhumblefish View Post
Yes, Brother Les, tank (and overpressure valve) working properly. Tractor Supply might have just been a little enthusiastic in adding propane to that one.

Hey, WMTire - Tanks were on the rig vertically, all the way to the propane resupply/ I pulled them off and handled vertically, the entire time. Filled with a giant tank and regulator setup, manually (I didn't see the TSC worker preset a PSI or weight). Then right back on the rig, and properly hooked right back up.

Tanks are new-ish from last year delivery of the Roo. I'm not saying anything was wrong with the tanks or how they were handled, I'm suggesting TSC simply put a little more propane in there than the tank should have received, above the 80% rule.
This is my point I'm trying to get at. Tractor Supply "shouldn't" have been possibly able to overfill them with a properly functioning OPD (overfill protection device) in the cylinder and/or proper fill techniques. That's why I am thinking there could be other issues.

The OPD is a float lever inside the cylinder. When the cylinder receives an 80% fill of liquid propane, the OPD closes to not allow any more liquid propane in.

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Old 05-16-2022, 12:19 PM   #6
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Interesting, I wasn't aware of how the OPD functioned. Maybe it was just a case of a completely full tank doing a little venting, and all was working properly (thank you, Gay-Lussac's Law). Tank was never anything other than horizontal, but I'll watch the tank. Never had a problem prior to this fill from TSC.

FWIW, the 'leak' was at the pressure release valve in the 9 o'clock position. Had a red plastic insert. Soapy water test showed this right away.
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Old 05-16-2022, 12:21 PM   #7
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When they are filling the tanks, is it the relief valve that they open with a screwdriver for venting? Is it possible they did not close it tightly enough and therefore the relief valve opened at a lower pressure than it was supposed to?
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Old 05-16-2022, 01:03 PM   #8
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When they are filling the tanks, is it the relief valve that they open with a screwdriver for venting? Is it possible they did not close it tightly enough and therefore the relief valve opened at a lower pressure than it was supposed to?
X2 The place I get mine filled at always opens the relief valve, and I always double check that it is tightened before putting them back in service.
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Old 05-16-2022, 10:43 PM   #9
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If the OPD float is functioning as it should, it makes it impossible to overfill the propane tank. The tanks themselves have dual threads at the outlet nozzle: an outer thread that is common for the large coupling nut that is standard for most connections and an inner thread for specialized applications. In both cases, the valve inside the outlet is pushed open when a nut is screwed onto the outside or inside thread. It does not matter if the valve is turned on or not…. There will be some gas present. You could have a cracked coupling but or a hairline crack in your hose that is allowing the propane to pass. In one case, I had a regulator that the inside rubber diaphragm had become brittle and was allowing the gas to escape.
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Old 05-17-2022, 12:42 PM   #10
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Thanks for the input, gang. I don't know that there's anything wrong (and don't really suspect that there is), other than a *completely full* tank that is simply off-gassing a
hair through its a BOV because it was in the sun for a while (aka working as designed). Tanks are new(ish), being freshly factory delivered last year and covered at all times (with indoor storage).

Tractor Supply didn't adjust the BOV or take any tool to the the tank in any way whatsoever, simply screwed on a fill line and ran the fill.

*shrug* I was really just sharing an anecdote.
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Old 05-17-2022, 12:57 PM   #11
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Tractor Supply didn't adjust the BOV or take any tool to the the tank in any way whatsoever, simply screwed on a fill line and ran the fill.

*shrug* I was really just sharing an anecdote.
Every tank that I have ever had filled at multiple places they have always vented the tank by opening the relief valve with a screwdriver.
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Old 05-17-2022, 02:13 PM   #12
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Every tank that I have ever had filled at multiple places they have always vented the tank by opening the relief valve with a screwdriver.

I fill tanks at U-haul, some employees open the relief valve, most do not.
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Old 05-18-2022, 01:53 PM   #13
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Over pressure

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I fill tanks at U-haul, some employees open the relief valve, most do not.
The relief valve should not be opened to fill. There is a bleed valve that should be opened just enough to bleed GAS during filling. When the liquid fills to this bleed valve, liquid comes out instead of GAS. At this point filling is complete. The bleed is closed. If this bleed is not opened during filling, the tank can be over filled. The top area of the tank should have GAS and liquid in the lower area. This area of Gas is what allows for the expanding liquid. When it get hot there is not enough GAS space for the expansion of the liquid. Pressure gets higher than the relief setting and bleeds GAS off. If the bleed valve is not used during filling get it done someplace else.
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Old 05-18-2022, 03:18 PM   #14
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Every tank that I have ever had filled at multiple places they have always vented the tank by opening the relief valve with a screwdriver.
That's because many are taught by old-timers from the pre-OPD era that it's still necessary.

The "outage valve" will show liquid at 80% and the OPD shuts all inbound at 80%.

On my tanks (03-17 date) the instructions state clearly that the use of the outage valve is OPTIONAL.

Had a tank filled Monday on way out of town. The operator insisted on opening outage valve while filling. I watched meter and it stopped about 20 seconds befor he finally closed valve.

All the valve accomplished was to create a stink.
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Old 05-18-2022, 03:36 PM   #15
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That's because many are taught by old-timers from the pre-OPD era that it's still necessary.

The "outage valve" will show liquid at 80% and the OPD shuts all inbound at 80%.

On my tanks (03-17 date) the instructions state clearly that the use of the outage valve is OPTIONAL.

Had a tank filled Monday on way out of town. The operator insisted on opening outage valve while filling. I watched meter and it stopped about 20 seconds befor he finally closed valve.

All the valve accomplished was to create a stink.
It's all a matter of pressure. There are two things that will stop the flow of liquid propane into the tank being filled (and really only one thing). The pressure inside the tank being filled equals the pressure of the source it is being filled from (and relieving that pressure via a relief valve solves that issue) or the overfill prevention device (float) closes which then causes the pressure at the inlet port of the propane cylinder being filled to equalize with the filling source to stop the flow of liquid propane into the tank.
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Old 05-18-2022, 08:22 PM   #16
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It's all a matter of pressure. There are two things that will stop the flow of liquid propane into the tank being filled (and really only one thing). The pressure inside the tank being filled equals the pressure of the source it is being filled from (and relieving that pressure via a relief valve solves that issue) or the overfill prevention device (float) closes which then causes the pressure at the inlet port of the propane cylinder being filled to equalize with the filling source to stop the flow of liquid propane into the tank.
Since liquid propane is being pumped into the tank at a high enough pressure to keep it in liquid state it will overcome any pressure of the gas in the tank. As pressure rises gas in the tank will return to its previously liquid state. Propane only needs 100-200+ psi for this to occur depending on ambient temp.

Liquid level is what stops flow into typical portable RV tanks with OPD Valves installed. Not gas pressure.

Also, no gas needs to be let out to fill. The outage valve is just a primitive "liquid level indicator".
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Old 05-23-2022, 06:37 PM   #17
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Overfill freezout

Im told that an overfilled tank can cause liquid propane in the lines to freeze and disable the regulator. More can be less.
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Old 05-23-2022, 07:13 PM   #18
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Im told that an overfilled tank can cause liquid propane in the lines to freeze and disable the regulator. More can be less.
That's why the OPD valves are now required. That and to also prevent an overfilled tank from venting liquid when warmed up by sunlight, etc which then vaporizes into a cloud of propane that can ignite from any flame/spark.

With a only 80% of the tank filled with liquid the remaining 20% provides a cushion for expansion and prevent unwanted venting of gas or liquid.
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Old 05-23-2022, 08:35 PM   #19
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Water droplets inside the connector can freeze the valve shut and prevent the tank from being filled.
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Old 05-23-2022, 11:41 PM   #20
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EPA regulation for gas emissions reduction reason for valve.

Federal regulations for the reduction of fugitive hydrocarbon emissions is the primary reason for the implementation of these OPD valves. An added benefit is the safety factor of not overfilling the tank.

As a side note, even the alcohol containing vapors from rising bread in large commercial bakeries requires emissions controls as do the return vapors collected by coaxial hoses installed on gas pumps in areas of the country with ozone compliance issues. Sometime the gas vapor is collected with a carbon canister and returned to the storage tank as liquid and in other cases a device with a vacuum pump and a heated electrical grid combusts the vapor.
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