Gas regulator question

On Liquid Propane tanks, say, the 20 LB tank on my gas grill, what is the pressure in the full tank and what is the pressure stepped down to on the low pressure side of the regulator?
How does this differ from regulators used to deliver Propane to Propane stoves, furnaces, and so forth?
I've heard that the "Outdoor-Use" regulators step down to deliver gas at 1/2 PSI, and that "Internal -Use" regulators step down to deliver gas at 2.0 PSI.
I'm wondering how to make an old propane furnace in my shop run on 20 LB cylinders, and need to understand the stepdown of the regulator and where to get one inexpensively. I already have all of the fittings to attach the tank directly to the furnace.
Let's leave code and inspectors out of this conversation for now.
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There are TWO regulators on a propane system. The first stage drops the tank pressure to 10PSI ( this is known as "high" pressure ) and the second regulator drops the pressure to the required level for the appliance. There are two types of "low" pressure regulators - a 2PSI version for large heating units and an "11 inches of water" version for most everything else.
Fisher makes both of these in many models depending upon how much gas needs to be delivered. You do know that the tank has a reverse thread on it, don't you?
http://www.fisherregulators.com/lp/pdf/lp31slct.pdf
Try eBay for regulators but only buy new in box units.
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Andy adds:
I have seen "10 inches" of water specified on a number of furnace devices. I thought I would just post what that means and what it means in psi.
10 inches of water means the weight of a square column of water 1 inch on each side which is 10 inches high .
To determine the psi; Remember 33.9 feet high (406.8 inches) and 1 sq inch on a side is 14.7 pounds
Therefore , 10 inches : (10/406.8) = (Xpsi/14.7) psi is 0.36 psi
11 inches : 0.40 psi
So, these pressures represent a very low, but still positive pressure.
Obiously, these very low pressures would be a pain to measure with a gauge, but really easy with a manometer , hence "inches of water".... Andy
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Where did you learn this? "of a square column of water 1 inch on each side"
You make it sound like the density of water is dependent upon the volume of it's container.

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Terry wrote:

I wonder if his manometer is a one inch by one inch square :-)

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Terry wrote:

each
volume of

Andy replies:
If the bolus of water is 1 inch on a side, the bottom area of the column is one square inch. Pounds per SQUARE INCH is the measurement we are interested in, so I used this as an illustration.
The WEIGHT of the water is dependent on the volume of the container ---- density is not the issue we are interested in. However, the DENSITY is what we are dealing with when when we say that 33.9 feet of water in a column one inch on a side, weighs 14.7 POUNDS...... Since the base of the column is ONE SQUARE INCH, the pressure is 14.7 pounds per square inch...
This is also known as ONE ATMOSPHERE, or, the pressure of a column of AIR , one inch on a side, extending from the earth to space, at standard temperature and pressure, exerts a force of 14.7 pounds per SQUARE INCH ,or ,ONE ATMOSPHERE....
Thats how I remember the value for water without having to look it up...
If you are diving in water , at 33.9 feet below the surface, the water pressure on you is 2 ATMOSPHERES, or, 29.4 psi.... ( Easy to remember if you take a scuba class)
Go look in the CRC tables, and it will list all this stuff. Also, a general science book from high school should give a similar explanation....
Sorry if my explanation was not in the manner that allowed you to understand it..... it worked for me, and that's how I remember it......
Finally,1 gallon of water = 231 cubic inches = 8.34 pound avor
You can work this backward and get the same answer.......
By the way, here's a GREAT rule of thumb.
1 foot of water is 1/2 psi. Not strictly precision, but real easy to remember and close enough for alt.home.repair.
Andy , BS, MS, PE etc.etc.etc

pressure.
a
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Andy adds :
One more thing.
"Eric" sent me an Email telling me that he worked for a gas company that used a little tube of clear plastic to determing the pressure. It was partially filled with water and one end open and the other connected to the pressurized line. A simple ruler, in inches, was used to determine the pressure......
Sure... That's called a "manometer". If you mount it on a nice stainless steel plate and put a calibrated ruler on it, you can buy one for between 10 and 1000 dollars, depending on the quality. Personally, I use the little plastic tube and my kid's ruler, since I don't need calibration to 4 decimal places (grin).
For very low pressures, you can't beat this method.
By the way, the LARGER the diameter of the tube, the higher the accuracy. It has to do with capillary action...... If you have a half inch diameter, it's pretty good......
As an out of class assignment, do a google search on "water levels", which is a way to us a very long plastic tube to determine that a very long piece of anything is level...... This stuff gets interesting when you start applying these principles to stuff you might need to do......
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Terry wrote:

Why did you come up with that critique? His explanation makes perfect sense and is correct.
I often explain water pressures developed by gravity the same way.
Happy Holidays,
Jeff
--
Jeffry Wisnia

(W1BSV + Brass Rat '57 EE)
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Jeff Wisnia wrote:

When I read Andy's statement I had the same impression as Terry. 10 inches of water has nothing to do with size of the column. On the other hand, you have to know the weight of a 1 inch square column to convert to PSI (pounds per square inch), which is what Andy said he was doing.
Pressure measurements are confusing because so many different measures are use. PSI is common to everyone, inches of water are used for low pressures. Inches of mercury are used for somewhat higher pressures. Atmospheres is a convenient measure for some work.
And, it is not easy for many people to find the conversion factors. Here are some:
Atmosphere -- 14.70 psi -- 1.058 tons per square foot-- 29.92 inches of mercury -- 33.90 feet of water
Inches of water -- 0.03613 psi -- 0.07355 inches of mercury-- 0.002458 atmospheres
By the way, the inches of water measure is based on 4 deg C and mercury is based on 0 C.
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George E. Cawthon wrote:

Andy replies:
You know, I had never thought of that. It's obvious from the state table that this temp is the max density of water at standard pressure.......
Thanks for pointing it out. It seems there are a number of things that I haven't run into before....... Andy
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George E. Cawthon wrote:

That's distilled (H2O) water I presume, not "heavy water" (D2O) which has a specifig gravity of 1.107. <G> Ice cubes made from D2O sink in regular water.
http://ptcl.chem.ox.ac.uk/MSDS/DE/deuterium_oxide.html
You can even buy it here:
http://www.unitednuclear.com/chem.htm
The town water where our business is located has enough bad taste to it that I bet it even has a different density.<G>
There's so much salt in it (from years of road salt finding its way into the well water.) that the town has to tell all property owners that if they are on a restricted salt diet, "Don't drink the water."
Interestingly enough, there's no town regulation requiring the property owners to inform office tenants like us, or apartment tenants. Seems like they should though. I happen to know about it because we lived in the town about 19 years ago and they were doing it then. Friends who live in the same town now tell me they still get notices in the mail from the town once a year.
We use a "MultiPure" brand filter ahead of our office water dispenser, and we use the same one at our home in the next town, though the unfiltered water at home tastes a lot better than the stuff at the office.
Happy Holidays,
Jeff
--
Jeffry Wisnia

(W1BSV + Brass Rat '57 EE)
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Jeff Wisnia wrote:

Ha. Ha. If you have heavy water, you've got too much time on your hands, or maybe your hands have been where they weren't supposed to be.
I thought the actual numbers might be interesting. But, yes, distilled water would be best, and put that water in a vacuum bottle to keep it the right temp! Actually for all practical purpose the difference in density within normal living temperatures and the difference in solutes of normal drinking water aren't going to make much difference in the measurement. Besides, the guy that decided 11 inches was correct or 7 inches in an RV system, just picked a ball park number. Stuff I've looked at that uses low pressures often allows a 20-30 or even 50 percent difference in allowable pressures. So even it you use water so salty you can't drink it to set the regulator, it is unlikely it would make any measurable difference to operation.
Wait till you get to a system where they decide the best way to add chlorine is to add a months supply in one day. That way you don't need to bother with adjustments for the rest of the month.
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One foot (height) of water make .434 PSI. So, 10 inches is a little less than .434 psi.
If you want to be exact, the formula would be
10 --------- x .434 = pressure in PSIG. 12
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Christopher A. Young
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