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 > Mysterious Propane "Leak"

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JimK-NY

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Posted: 10/19/22 09:50pm Link  |  Quote  |  Print  |  Notify Moderator

A drop in temperature would decrease the propane pressure. The drop is insignificant. During my testing, the temperature dropped from about 60 F to about 50F. Pressure of a gas is directly related to absolute temperature in degrees Kelvin. 60 degrees F is about 493 degrees Kelvin. 50 degrees F is about 487 degrees Kelvin. So the drop in temperature and the drop in pressure were insufficient at only a bit over 1%.

3 tons

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Posted: 10/20/22 08:49am Link  |  Quote  |  Print  |  Notify Moderator

JimK-NY wrote:

A drop in temperature would decrease the propane pressure. The drop is insignificant. During my testing, the temperature dropped from about 60 F to about 50F. Pressure of a gas is directly related to absolute temperature in degrees Kelvin. 60 degrees F is about 493 degrees Kelvin. 50 degrees F is about 487 degrees Kelvin. So the drop in temperature and the drop in pressure were insufficient at only a bit over 1%.


Not to get tooooo far into the weeds, but here’s a temp vs pressure chart:

https://www.propanewarehouse.com/helpful-information/lp-gas-properties/

3 tons

JimK-NY

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Posted: 10/20/22 12:09pm Link  |  Quote  |  Print  |  Notify Moderator

Thanks, that is an interesting web site. Those temp/pressure tables really do not apply to this topic. They are about vapor pressures over liquid propane, not about temperature changes in pressure for propane in a gas state.

wolfe10

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Posted: 10/20/22 05:46pm Link  |  Quote  |  Print  |  Notify Moderator

JimK-NY wrote:

Thanks, that is an interesting web site. Those temp/pressure tables really do not apply to this topic. They are about vapor pressures over liquid propane, not about temperature changes in pressure for propane in a gas state.


????

PV=nRT.


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Bobbo

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Posted: 10/20/22 08:05pm Link  |  Quote  |  Print  |  Notify Moderator

JimK-NY wrote:

Thanks, that is an interesting web site. Those temp/pressure tables really do not apply to this topic. They are about vapor pressures over liquid propane, not about temperature changes in pressure for propane in a gas state.

Ummmm, "vapor pressures over liquid propane" IS "propane in a gas state." The material BELOW the "propane in a gas state" is liquid propane.


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JimK-NY

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Posted: 10/20/22 09:30pm Link  |  Quote  |  Print  |  Notify Moderator

PV=nRT applies to all gases including propane. I showed the calculations above for the variation in temperature that occurred for my last leak test. Temperature for the universal gas law is expressed in degrees Kelvin. A drop of 10 degrees F was only about a drop of a bit over 1% in Kelvin degrees so the pressure would have dropped by that same small amount.

The tables cited by 3tons are for vapor pressure over liquid and would not apply for a leak test with no liquid in the system and the tank valve closed. The tables are quite useful for other purposes. As we can easily experience vapor pressure of gaseous propane over liquid propane changes greatly with temperature. This reflects a decrease in the rate at which gas can be produced from liquid propane. The tables show a substantial drop in the ability of various sized propane tanks to provide gas for heating or other purposes. The drop is so bad I long ago stopped trying to use a propane BBQ in the winter months.

3 tons

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Posted: 10/21/22 12:44pm Link  |  Quote  |  Print  |  Notify Moderator

For the uninitiated, here’s the (above referenced…) ideal gas law, but then again this seems to be delving more into abject nuance than application…Bottom line with gasses remains when temperature goes up pressure goes up (this was my only point…), though I have no idea if this is the true cause of the OP’s particular issue:

https://sciencetrends.com/in-pvnrt-what-is-the-r-constant/

3 tons

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