Propane level gauge- howzit work?

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Propane level gauge- howzit work?

Postby fastED » Thu Jan 08, 2009 7:58 pm

Ebay has an in-line analog propane tank level gauge. You've probably seen them, about 25 or 30 bucks. How do they work? The vapor pressure of propane is constant, regardless of propane level in the tank, right? Like I have said many times before.........I don't get it..........
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Re: Propane level gauge- howzit work?

Postby Larwyn » Thu Jan 08, 2009 9:33 pm

fastED wrote:Ebay has an in-line analog propane tank level gauge. You've probably seen them, about 25 or 30 bucks. How do they work? The vapor pressure of propane is constant, regardless of propane level in the tank, right? Like I have said many times before.........I don't get it..........


They work exactly as you said, and are just as useful as you stated. I purchased two of them when I got my 5th wheel trailer. Only used them once. They are very accurate when the tank is empty, anything between empty and full reads purty much the same. They are a waste of money and a stupid application of a pressure gauge, but they serve their purpose, which apparently is to separate the uninformed from their money. I'm informed, now but that did not prevent my wife from getting one as some kind of a gift, so between us we have three of them, each one as useless as the next.

They would however make good paper weights, the gauges might look somewhat impressive if included in some kind of industrial art, and as I have already stated when used on a propane bottle they are absolutely accurate when the bottle is empty.... :lol:

All kidding aside they are useful when checking for leaks. You connect the gauge between the tank and the pigtail to the system. Turn on the propane valve to pressurize the system. Then turn the valve off. Go away for a while. Come back. If the pressure has dropped on the gauge you have a leak somewhere. That's about as useful as they get.

I'd sell you all of mine cheap, if I could find them............ :lol: :lol:
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Postby Jiminsav » Thu Jan 08, 2009 9:34 pm

it doesn't work..the pressure drops JUST before it runs out..which you'll have noticed when the fire got cold anyways. get one of the thermal ones you stick to the side, they more accurate indicator of the level of liquid left in the tank.
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Postby Dale M. » Fri Jan 09, 2009 12:01 am

Actually pressure in tank is temperature sensitive... IF tank is really cold pressure drops, gauge reads near empty... Warm tank up pressure increases, tank reads full.......

There ARE two accurate way to tell how much liquid that is in tank...

First is by weight... Propane weighs 4.25 pounds to a gallon and a 20 pound tank holds 4.8 gallons.... 4.8 x 4.25 = 20.4 pounds for propane...

Put tank on scales, and get total wight of tank+propane and then subtract "tare weight" of tank (stamped on safety collar- usually 18-20 pounds), and remaining weight can be converted to how many "gallons" of liquid remains...

Other solution is to heat a pan of water (quite hot) and dribble it over side of tank (take your time heat has to transfer from water to steel tank).... then slide your hand down side of tank, there will be a "line" on tank where upper part of tank is warm, below line tank will be cool... The is level of propane in tank... This is same principle where "liquid crystal strip" tank indicators work...

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Postby sdtripper2 » Fri Jan 09, 2009 1:24 am

FastEd:

I too have been wondering about those gauges. And as the
(Keeper of the Most Out Of Control Shop (2005), (Larwyn)
and our own Jim in Savannah (Who will always take
money)
have concluded the analog gauge seems to be junk. I unike
Larwyn have access to the one I bought and would gladly sell it to you for
a hamburger next week.

After studying tonight about the magic that goes on inside the propane
bottles I have come away with a better understanding. I honestly didn't
know like yourself how the pressure and propane came out of those bottles
in theory.

So here it is in a nut shell:

Given:
Propane gas becomes liquid with a little pressure.

At fill time a specific amount is filled and it boils off in the atmosphere of
the tank to equalize pressure with liquid on the bottom of the tank and
boiled off gas at top (Waiting for the chef to turn da valve).

Scenario:
A full propane bottle sets there waiting for a change of valve pressure (gas out to your stove etc.)

At the moment of air temp change of valve opening the gas that has boiled
off at the top of the bottle flows out, and immediately the liquid
propane boils again and releases more gas to equalize the pressure. This is
done almost imperceptibly. UNTIL there is just a bit of liquid gas or empty
and then an in line gauge would say empty. The gas is Temperature sensitive
so gauge will fluctuate See this pdf file for Temp chart and read more at
the link below.
(Thus in our opinions a worthless gauge,
except for telling leaks as in gauge reads empty
and you didn't use your bbq ... duh... ya have a leak)


So there you have it ... the in~ine gauge is basically a FULLl / EMPTY gauge for 25 bucks. :roll:

Read Click Here for much more information and for other ways of telling how full your tank is.
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Postby john » Fri Jan 09, 2009 8:04 am

I just watch for the condensation/frost that forms on the side when in use. May work better in humid areas. :thumbsup:
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Postby sdtripper2 » Fri Jan 09, 2009 8:40 am

How can I tell how much LPG is left in the cylinder?
There are a number of ways to check this:
· Firstly, a cylinder can be weighed to check how much product is left in
the cylinder. The weight of the LPG remaining in the cylinder is total weight
of the cylinder plus the LPG, less the empty weight or tare weight, of the
cylinder. (The regulator and any other fittings should be removed prior to
weighing the cylinder).
· Secondly, some cylinders have gauges which show the amount of :roll:
LPG contained within the cylinder. The in-line gauges are less desirable
than the in-tank gauges that have floats that sense exact liquid level.
(This in-line gauge is one that is the FULL / EMPTY gauge for 25 bucks.)
See The Tank and SureFlame advertisements for in-tank float gauges.

Thirdly, liquid crystal gauges, which stick to the outer surface of the
LPG cylinder are available, and these show the level of the liquid LPG within
the cylinder by indicating a colour change at the interface between the
liquid and vapour levels caused by the temperature variation.
· Fourthly, if the cylinder is being used, then it may be possible to see
the level of the LPG in the cylinder by observing the level of the sweating
on the cylinder wall
. (This is John's suggestion and I agree this works fur sure.)
· Lastly, it is possible to see the level of the LPG liquid within a cylinder
by pouring boiling water down the side of the LPG cylinder. The liquid level
is revealed where a condensate or frost line occurs.
***
What does a 20lb propane cylinder weigh when empty?
17-18 pounds, depending on the manufacturer.

How long on average does a 20 lb propane gas grill tank last?
1 gallon of Propane ~= 4.23 lbs ~= 91500 Btus
1 lbs of Propane ~=22000 Btus
20 lb tank of propane holds approx 4 gallons of propane (366000 BTUs)
Your grill will last 366000 BTUs/ Grill BTU output hrs
WikiAnswers
****
Last edited by sdtripper2 on Fri Jan 09, 2009 3:53 pm, edited 2 times in total.
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Postby campadk » Fri Jan 09, 2009 9:32 am

I have two gauges that I have added to each of my 2 tanks on the Airstream. They work well for me. Not super accurate, but they certainly give me a good sense of whether a tank is fairly full, or getting low/needs refilling. I would buy them again in a snap!

Didn't buy them here, but this looks like the versions I bought...

http://www.northlineexpress.com/itemdes ... L-TVL-212P
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Postby brian_bp » Fri Jan 09, 2009 2:21 pm

sdtripper2 wrote:Secondly, some cylinders have gauges which show the amount of :roll:
LPG contained within the cylinder. (This one is the FULLl / EMPTY gauge for 25 bucks.)

Yes and no. Most gauges which are built into common "barbecue" (20-lb) tanks are indeed simply those nearly useless pressure gauges. The exception is Manchester's SureFlame, which is an actual level gauge. The dial is a clip-on accessory, which is magnetically coupled to the float inside which triggers the OPD valve. It provides an actual (if not terribly precise or accurate) level indication.
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Postby sdtripper2 » Fri Jan 09, 2009 4:13 pm

brian_bp wrote:
sdtripper2 wrote:Secondly, some cylinders have gauges which show the amount of :roll:
LPG contained within the cylinder. (This one is the FULLl / EMPTY gauge for 25 bucks.)

Yes and no. Most gauges which are built into common "barbecue" (20-lb) tanks are indeed simply those nearly useless pressure gauges. The exception is Manchester's SureFlame, which is an actual level gauge. The dial is a clip-on accessory, which is magnetically coupled to the float inside which triggers the OPD valve. It provides an actual (if not terribly precise or accurate) level indication.


Brian I have edited the post above and the other post in the camping secrets section to reflect the different in-line and in-tank float gauge differences and pointing to the in-tank float gauges as being a better solution.

Secondly, some cylinders have gauges which show the amount of :roll:
LPG contained within the cylinder. The in-line gauges are less desirable
than the in-tank gauges that have floats that sense exact liquid level.
(This in-line gauge is one that is the FULL / EMPTY gauge for 25 bucks.)
See The Tank and SureFlame advertisements for in-tank float gauges.


camping secrets section edits
Two inside tank float sensors that work well for an external gauge
Advertisements:
The Tank© is a product on the market that gives an accurate,
reliable measurement of the level of liquid propane left in the tank.
***

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SureFlame

***
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Postby TinKicker » Fri Jan 09, 2009 5:18 pm

Following this thread, I thought of the propane tanks on our company forklift. They're cigar shaped and mount horizontally, so you grab the handle at one end and pull the tank off the "trunk" of the forklift to remove them.
The gauge on them will flutter as the tank moves from horizontal to vertical, so they must have floats in them. That apparently is a good design because we've used them for MANY years on two different lifts, and they're still accurate.
Just my experienced two cents.
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Postby BPFox » Fri Jan 09, 2009 8:20 pm

Here's how I tell, when the flame goes out, time to change the tank. It's kind of a simple system, but it works every time.
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Postby sdtripper2 » Fri Jan 09, 2009 8:50 pm

BPFox wrote:Here's how I tell, when the flame goes out, time to change the tank. It's kind of a simple system, but it works every time.


BP you sly fox you :R

Many a person has taken your sage advice to heart. :thumbsup:

Just to reset this thread... the question was from fastEd: wrote:Ebay has an in-line analog propane tank level gauge. You've probably seen them, about 25 or 30 bucks. How do they work? The vapor pressure of propane is constant, regardless of propane level in the tank, right? Like I have said many times before.........I don't get it..........


A few of us agree with fastEd that the pressure in the propane (LP) tank
stays constant almost till it is empty because of the way the LP liquid under
pressure boils off inside to keep the pressure constant. We are firmly in the
camp of the IN-LINE Gauges are not very accurate for that reason.

Dave says he likes the IN-LINE Gages he has on his Airstream two tank
system. As he has two tanks he doesn't have the same worries if one of his
tanks goes empty without his gauges reading precisely.

Brian brings into focus that IN-TANK float outside gauge products are
available to have very accurate assessments of propane in tanks.

Others believe in the touch, condensation, sensor on side of tank or hot
water pour methods of observation. These are well respected.

Then there is YOU BP and most likely many more out there that use your 8)
system of propane available when the knob is turned = A-OK. If not then
there is an Aww-sh!t sound and a scrambling to get more.
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Postby brian_bp » Mon Jan 12, 2009 2:42 pm

Thanks for the updates, Steve. I had not heard of The Tank before. Unfortunately, it appears to be even more expensive than the Manchester Sure-Flame, and less available.

TinKicker wrote:Following this thread, I thought of the propane tanks on our company forklift. They're cigar shaped and mount horizontally, so you grab the handle at one end and pull the tank off the "trunk" of the forklift to remove them.
The gauge on them will flutter as the tank moves from horizontal to vertical, so they must have floats in them....

Yes, lots of propane tanks have proper level gauges in them, including most built-in tanks, these forklift tanks, larger upright portable tanks (generally a couple hundred pounds and larger), and even 20 lb to 40 lb horizontal portables; they're all floats as far as I know. It seems to me like it's only the common cheap things we use for barbecues and RVs that don't have gauges.

A forklift tank would be appealing for a trailer, except that (I believe) these are set up for liquid service, and we need vapour.
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Postby brian_bp » Mon Jan 12, 2009 2:44 pm

BPFox wrote:Here's how I tell, when the flame goes out, time to change the tank.

:rofl:

But seriously, losing the ability to cook and heat in the middle of a trip is not fun. I assume that my travel trailer has two tanks only so the second one can be used as reserve, not because people commonly use 40 lb of propane in one trip.
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