RV Propane Header Pressure

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jason.hampton

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I have a 2006 Jayco Jayflight (Model 31 BHDS). I want to put a pressure gauge in my propane header to view the current PSI. What is the normal operating pressure for a full tank. I have two of the large bottles, if that makes a difference. I believe they are 30lb bottles.

Best Regards,
Jason Hampton
 
I am not sure, if you put the gauge before the regultaor it will read kind of like this

Full, Full, Full, Full, Full, Full, Full, Full, Full, Empty

The pressure at this point is a function of tank temperature not the level of propane in the tank.

After the regulator, Same result, the pressure here is roughly 1/2 PSI or 11" of Water (The pressure of a collumn of water 11 inches high).

In short, you plan will not work as you hope (Tell you half full for example)

Only three ways to do that I know of

one is weight
one is a float inside the tank (requires modifications to the tank)
One is to pour boiling water over the tank after attaching a LCD strip the color change point is the level of liquid..

You can also "Sound" the tank, some folks are good at it and if you are drawing gas fast enough feel the temp boundry.
 
You can buy a propane "gauge" in many places that have LP equipment or grills - here is one:
http://www.walmart.com/ip/Propane-Tank-Gauge/13350316

The problem is as John described: the tank pressure stays well up as long as there is much of any LP in the bottle, but drops precipitously toward the end. And temperature can have a dramatic effect once the tank gets down a bit.  That said, having this sort of pressure gauge is better than no warning at all, especially if the tank is not easy to get at to "heft it" to check the weight.
 
Welcome to The RV Forum, Jason!

The reason measuring the tank pressure doesn't tell you much is because propane isn't stored as a compressed gas.

It's stored and pumped in liquid form, and the propane in your tank is a pool of liquid propane with a gas vapor bubble on top.  When you draw propane gas out of the bubble, more liquid boils off to take it's place and the pressure remains constant until you've used up all of the liquid.

Liquid propane is 270 times denser than the gas - 1 cubic foot of liquid propane makes 270 cubic feet of propane vapor.  So your tank is essentially empty when the liquid's gone and the tank pressure starts to drop.

The tank pressure will range from around 100 to 200 PSI, but that's determined by the tank temperature, not the quantity of propane in the tank.

A propane distributor may be able to install a replacement tank valve with a fuel level gauge built-in, but these are fairly expensive and specific to the height of your tank.  They work like the fuel gauge in your car, driven by a float riding on top of the liquid propane in the tank.

If you pour a cup of hot water down the side of your propane tank, there will be a temperature difference at the level of the liquid propane, because the liquid absorbs heat much more readily than the gas above it.  Sometimes the hot water will reveal a condensation line at the liquid to vapor level, or you can feel the difference with your hand.

Or you can get a temperature sensitive liquid crystal strip that sticks to the side of the tank and works on the same principle - when you pour hot water on it the strip changes color where there's gas on the other side of the metal, but doesn't where it's next to the heat absorbing liquid propane.
 
jason.hampton said:
I have a 2006 Jayco Jayflight (Model 31 BHDS). I want to put a pressure gauge in my propane header to view the current PSI. What is the normal operating pressure for a full tank. I have two of the large bottles, if that makes a difference. I believe they are 30lb bottles.

Best Regards,
Jason Hampton

It depends on temperature.  There's a chart here:

http://www.pveng.com/ASME/ASMEComment/ASMEComment.php

As Lou said, a pressure gauge won't tell you how much propane is left.  For that you need a float gauge inside the tank.  My TT came with float gauges.  If you want to retrofit, tanks with float gauges are available from several sources, but they are expensive.  I have use Vintage Trailer Supply for related projects:

http://www.vintagetrailersupply.com/30_Vertical_Aluminum_Tank_p/vts-169.htm
 
Here is a link to  cylinders thar are translucent, lightweight and non-corrosive. Only wish they made them in a larger size.
http://www.litecylinder.com/products.aspx
 

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