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ERBenoit
01-14-2010, 09:06 AM
I'm helping a friend of mine install a L.P. heater in his infrequently used garage. The manual calls for incoming pressure to be between 11-14 inches of water. Those "/H2O gauges are expensive.

What does 11-14" water convert to in P.S.I.??

Evan
01-14-2010, 09:10 AM
1 psi = 27.7 inches of water column

Carld
01-14-2010, 09:12 AM
At sea level it's 1 psi = 27.7" of water column.

Evan
01-14-2010, 09:20 AM
Sea level makes no difference. 27.7 inches of water weighs one pound per sq inch of area.

Willy
01-14-2010, 09:31 AM
11=14" of water = about .4-.5 PSI.

Nope your tire gauge won't do.
But you already knew that. Now you know why the gauges are so expensive.

EVguru
01-14-2010, 09:41 AM
Inches of H2O gauges are expensive!?

Here's a radical thought, why not make a gauge that uses water in a tube and measure the inches.

Carld
01-14-2010, 09:43 AM
But air pressure is not 14.7 psi at 10 or 20,000 feet. Does the weight of water change in relation to the change in atmospheric pressure at various altitudes?

Carld
01-14-2010, 09:48 AM
He could make a manometer to measure the pressure but a column of water to measure 14 psi would be about 407.19 inches tall.

Evan
01-14-2010, 09:55 AM
A manometer is not referenced to atmospheric pressure, only to local gravity. It's called a Manometric unit. While gravity does change with altitude it isn't enough to matter.

Blueskys
01-14-2010, 09:56 AM
Sea level makes no difference. 27.7 inches of water weighs one pound per sq inch of area.

Atmosphreric pressure would change when away from sea level.
But I think most H2O" gages read relative to atmospheric pressure.
A bourdon tube has atmospheric plus process pressure on the inside
and just atmospheric pressure on the outside?
So take the same system intact to the beach and the gage should
read the same H2O"? I think.
But I'm sure there are instruments that read total pressure in which
case elevation would matter? I think.

Evan
01-14-2010, 10:01 AM
All about manometric measurement: Atmospheric pressure is not a factor.

http://ixian.ca/pics7/manometer.gif

Black_Moons
01-14-2010, 10:06 AM
carld: What? he said he wants to know what 11~14" of H2O collumn is in PSI, not measure 14psi with a water collumn.
EVGuru: Exactly!

To everyone going on about realative/absolute: Its a friggen propane heater, its gonna be refrenced to atmospheric pressure k? its 1/2psi of pressure, a very standard service pressure. My friends propane heater says the exact same thing. they make premade hoses that go from propane tanks, with the proper regulator going to diffrent fittings, the fitting depends on the pressure/etc, so you can't even buy a hose that will fit but has the wrong regulator (Im sure someone will go off and make a custom hose thats wrong and sell it just to prove me wrong now but ANYWAY).

You don't measure it, you don't even need to know what it is. you just hook it up to the proper regulator designed for it. They standardised all this stuff so people would'nt blow themselfs up, thats why they sell the premade hoses at even low end hardware stores like home hardware.

Carld
01-14-2010, 10:15 AM
Evan, the above page says the same thing I am, that altitude does affect the reading. The density of the water, the gravity change(which would be small) and the atmospheric pressure would all together make 1 psi rated at sea level be different at altitude.

An open end manometer at sea level would read 27.7 column inches with 1 psi applied to it. Taken to 10,000 feet the column would be higher with the same sea level 1 psi applied to it because the atmospheric pressure is lower. If the standard for 1 psi changes with altitude then it would still be 27.7" but I thought standards were standards and did not change with conditions.

Doozer
01-14-2010, 10:17 AM
Good stuff here. Evan, thanks for the info.
I copied the GIF image with the data to my
reference files for future reading. Very handy.

At a yard sale some time ago, I bought a gas
pressure gauge that reads in inches of water
and inches of Hg. I think it converted to
1 1/4 psi max for the gauge. I could peg the
needle just by blowing in it. No other gauge
I have ever had could do that. I have tried to
get past girlfriends to try to apply suction to
a vacuum gauge, just to see how well they
could do. I think only one was keen on the
idea. Anyhow, this gas pressure gauge was in
a hinged metal box, permanently affixed.
I think I payed \$3 for it. I think I used it for
adjusting a propane fork lift once.

--Doozer

Carld
01-14-2010, 10:19 AM
Black_Moons, we're off on a different tangent now, join us and have fun.:D Actually Willy gave him the right answer but we're having fun now, don't interrupt us.

ERBenoit
01-14-2010, 10:22 AM
carld: What? he said he wants to know what 11~14" of H2O collumn is in PSI, not measure 14psi with a water collumn.
EVGuru: Exactly!

To everyone going on about realative/absolute: Its a friggen propane heater, its gonna be refrenced to atmospheric pressure k? its 1/2psi of pressure, a very standard service pressure. My friends propane heater says the exact same thing. they make premade hoses that go from propane tanks, with the proper regulator going to diffrent fittings, the fitting depends on the pressure/etc, so you can't even buy a hose that will fit but has the wrong regulator (Im sure someone will go off and make a custom hose thats wrong and sell it just to prove me wrong now but ANYWAY).

You don't measure it, you don't even need to know what it is. you just hook it up to the proper regulator designed for it. They standardised all this stuff so people would'nt blow themselfs up, thats why they sell the premade hoses at even low end hardware stores like home hardware.

Thank You!!! All I was looking for is this = that, not start a debate about it.

I was able to score several brand new low pressure service regulators and will be using one for this application. We'll be starting witha 100# LP tank. Maybe I should have made that known.

The gauge is marked off in 1/4 P.S.I. increments. I think by the graduations on the gauge, I can set the outlet pressure pretty damn close to .4/.5 P.S.I.

Carld
01-14-2010, 10:24 AM
There ya go ERBenoit, now back to the discussion at hand. Grab some coffee, I want to learn why I what I think is wrong.

Evan
01-14-2010, 10:29 AM
In that vein...

A manometer is a balanced pressure device. When reading zero pressure the local atmospheric pressure is equal on both legs and so doesn't affect the reading. That's why a sphygmomanometer doesn't have a barometric pressure compensation.

Blueskys
01-14-2010, 10:32 AM
Debates are good. They force you to face unwarrented pre-conceptions
that may be misleading you.
Best if it doesn't get personal though.

Carld
01-14-2010, 10:33 AM
Evan, so what your saying is that the standard of 1 psi is not a standard at all and does vary with altitude?

Evan
01-14-2010, 10:35 AM
No, it's just not referenced to local atmospheric pressure.

Don't confuse a manometer with a barometer. The barometer is affected by local pressure since it is referenced to a vacuum.

Carld
01-14-2010, 11:17 AM
So, from what I have read at some sites:

A manometer pressure is only relative to the altitude at which it is used.

The standard of pressure is 100 kpa which is somewhat less than 14.7 and was adopted as the standard.

An open pressure gauge would be affected by ambient pressure while a closed pressure gauge would not and the closed gauge would use the sea level standard as "0" by having a vacuum on the closed area. But then wouldn't the vacuum on the chamber cause the needle to show below "0" at altitude?

So, in effect a standard pressure gauge would read different at different altitudes because they are open gauges. The open gauge would read pressures as the manometer does because it is affected by ambient air pressure.

As I see it the manometer and a standard pressure gauge(open gauge) would read the same at any given altitude which they were used side by side using inches of water to compare the readings.

Dawai
01-14-2010, 11:22 AM
OKAY>>>> ORGINAL question.. most plumbers, who's iq is lower than whale manure..

they get under there, adjust flame size, then adjust "flame color" on the settings, check it with a gauge. and Leave with a nice bill signed.

Very few people can "calibrate it" and Yes.. Evan is right about the loop, they "incline" the manometer to increase visual accuracy to perceive the proper value.

And, you left "temperature-density out of the equation".. but.. most the time, who cares..

I watched a boy wind a wallace and tierman box up, the needle looked like a helicopter for a second. He was confused.. I lost my calibration tool.

im#2
01-14-2010, 11:51 AM
May I add my 2 cents worth? I am a propane delivery driver in the state of Colorado and to be legal here you have to take a course and pass a test one part of which includes how regulator work and the adjustment if required.
Very seldon do you need to adjust one and by national fire code now to run anything to a house you have to use a two stage regular much like the new two stage regs in use in our better cutting torch rigs. It has nothing to do with any hose is made up or home made.
You are dealing with a liquid propane which had to vaporize to be used so be sure and attach the 100 lb bottle to a good anchor to keep it upright and it should be away from any door or windows 5 ft and the same from the house.
Yes, 1/2 lb is real close for the converted pressure but a manometer is the right tool to use if you have to adjust pressure and yes the pilot and air to the flame does need to be adjusted. Its sad that plummers are held in such low esteem as most do very well at that their job.

Carld
01-14-2010, 01:08 PM
To add to that, a plumber and electrician have to be licensed and a machinist does not.

philbur
01-14-2010, 02:05 PM
A manometer is a differential pressure gauge. It compares the pressure of the gas in the container to the local atmospheric pressure. Differential pressure is the factor that primarily controls the flow rate of gas out of the gas container, the manometer tells you what you need to know. The absolute pressure in the reservoir is equal to the local atmospheric pressure plus the measured manometer pressure. All normal dial type gauges (bourdon tube type) are differential pressure gauges. That’s why it’s called gauge pressure as opposed to absolute pressure.

Phil:)

Carld
01-14-2010, 03:42 PM
Thanks Phil, I think I understand it now. :D

derekm
01-14-2010, 05:43 PM
I atmosphere ~ 1 bar ~ 10m of water ~ 33ft water ~ 760mm Hg ~15psi

Dawai
01-14-2010, 06:04 PM
I apologize if I insulted the "real plumbers".. the licensed ones.. The majority of the ones around here are not. The Licensing test, they have to build a 3 story apartment complex parts list and proper venting design including a laundromat. THE Steamfitters local Chattanooga Tn, they have some real plumbers.

I was really amazed to discover that non licensed plumbers are trusted with fire control in homes. And yes, if you diddle the gas pressure-mix up, you can burn the place down.

My first experience at "iv tube water" manometers was a carburetor calibration tool for the Jap bike I had in 1973. Kool aid in the water helps see it. The trick there was getting the vacuum even on all carbs.

HSS
01-14-2010, 06:22 PM
I atmosphere ~ 1 bar ~

Most of the bars I have frequented (in the long lost past) didn't have much of an atmosphere.:rolleyes:

Patrick

Don Young
01-14-2010, 10:38 PM
Probably the easiest way to measure 11-14"H2O of gas pressure is to see how deep under water you have to stick the end of the hose for the gas to quit bubbling out. Could be dangerous for inflammable gases but is how such gages are often calibrated (generally using air or nitrogen).

rdfeil
01-15-2010, 12:09 AM
Evan is very right about a manometer, they read in reference to local atmospheric pressure only. So atmospheric pressure, elevation etc. have no effect on the reading. Another use for a 'manometer' is a long reaching level. A manometer is nothing but a U shaped tube that is filled with a measuring fluid (several fluids are used for various reasons), water is common. If you have a long clear plastic tube, say 400 feet for my example, and you go out to the local football field and want to mark the bottom of the goal post uprights at the same elevation (not necessarily the same height above ground) you do the following... run the tubing up the goal posts with it running down the field (a very long U). Now put the end of the tube on one goal post where you want the elevation to be. Now fill the tube with water (be careful to get the air out after filling). Top off the tube with water. Now go to the other goal post and where the water level is in the tube is the same point as the water level at the other end (the end of the tube). This will work at any elevation :D . Now on the same note if you were to apply 1 PSI of pressure to the reference end the level at the other end will be 27.3 inches higher.

On another note, pressure gauges can be purchased in many configurations. The most common is referenced to local atmospheric pressure, technically this pressure is called PSIG (Pounds per Square Inch Gauge). Another is referenced to a perfect vacuum and are called PSIA for Absolute. These gauges will read 14.x at sea level with the port open to the air and a certain barometric pressure. The last is a differential gauge- PSID this gauge brings out both the pressure port and the reference port for use. This type of gauge might be used to monitor a filter for replacement. As the filter plugs up the pressure loss will show on a differential gauge.

In my business I use a lot of pressure transducers that are of the submersible type. This is a differential type measurement. The reference port is connected to a small tube which is embedded in the cable to the transducer. The measurement port is the face of the transducer. The reference tube is connected to a bellows (think balloon with no pressure in it) and then the measurement is now based on the weight of the water or other nastier effluent on the face relative to the local atmospheric pressure. A 40 foot water tank will measure about 17.32 PSI when full (only the water pressure in the tank, not the pipe pressure of supply pressure). This is how we control levels in reservoirs and underground tanks. I have even measured the depth of our local river for kicks :p .

I hope this gives some help and insight.

Robin

Black_Moons
01-15-2010, 10:40 AM
Hmmm, PSI, i'll have to add that to my list of level senseing solutions iv considered for verious projects (mechanical float attached to arm or screw, mechanical float with magnets and hall sensore, mechanical float with optical sensore, ultrasonics with or without float tube, weight of tank, electrical conduction sensores

rdfeil: What kinda price can you get one of those electrical 2~psi sensores? I actualy recall one guy whose making 'fish robots' who uses vacuum refrenced PSI sensores but he says his cost \$600. I think he did'nt shop around.. :P Course, his are good to like 1~2" depth accuracy

Abner
01-15-2010, 10:55 AM
I have built and used my own manometer for years doing exactly what you are doing.
Take a piece of plywood 24" tall. Mark lines every 1/2" horizontally. Make the line in the middle 0 (zero)
attach a clear plastic tube in a 'U' shape.
fill with water until it levels out at the zero line.
You now have a manometer
attach a flexible piece of tubing to either end of the clear tubing, and connect to the (edit) burner side of your gas valve with the appropriate fitting.There should be 1/8 in port for doing this.
Pressures are set while the unit is working. Hopefully they are not to out of wack or you will have problems to get it to light safely/uniformly. I count to 5 if it doesn't light then I stop.

Your pressure is THE TOTAL difference beyond zero of both tubes added together on your manometer. (+7") plus (-7") = 14 inches of water column.

JoeFin
01-15-2010, 11:08 AM
Probably the easiest way to measure 11-14"H2O of gas pressure is to see how deep under water you have to stick the end of the hose for the gas to quit bubbling out. Could be dangerous for inflammable gases but is how such gages are often calibrated (generally using air or nitrogen).

Thanks Don - you accurately described what we call a "Bubbler" Presure/level device which would accurately make the measurement as required.

BTW: the diameter of the hose/straw makes no difference

Dawai
01-15-2010, 12:01 PM
Yeah, bubbler.. Used to put them in to measure liquid depth.. Stand a piece of pipe up in the water, you attache a flow rotameter (flowmeter like on a mig welder) and a regulator, the "pressure DP cell" at the top in the nice clean enviroment. Hook the air to it, any pressure exceeding the "water column" at the bottom of the bubbler tube just bubbles out. Retained pressure in pipe equal water column pressure which the instrument measures in the nice clean enviroment at the top.

I saw a galvanized one inch bubbler pipe bent over double in a sewage plant in Dalton.. Aligator? large turtle? no clue.. I know turds don't get that big. A grate was lifted and it was GONE.. whatever it was gone No threat to me. Thou I did look around while I was there.

Boucher
01-15-2010, 12:16 PM
Why not get a simple water level. They are cheap at the box stores, or they are easy to make. Run the gas into one side through a T and plug the other side of the T when you want to take a reading. Use a ruler to measure difference.

Dawai
01-15-2010, 07:26 PM
IV tube works. It's clear.. be careful dumpster diving for haz-mat materiels.. come up looking like a sea urchin with all the syringes..

KDuffy
01-16-2010, 07:55 PM
All you need is about 8 feet of 1/4" ID tubing a yard stick, a little duct tape, a 1/4" hose barb with 1/8" MNPT, and a cup of water. It will be much more accurate than guessing a gauge. Keep it vertical as was stated earlier and start with lower pressure and work up. Good luck!