OT: any steam heat wizards here?

[wmgeorge]

Steam pressure gauges are always mounted on top of the boiler, never in the water. Link to a proper Steam Table chart. Steam-Tables.pdf (byworth.co.uk) Yes I have actually worked on steam boilers and remember the gauge reads in PSI not Absolute. Water in column 1 ft high and 1 inch in diameter weighs .433 lb.

[gellfex]

Steam pressure gauges are always mounted on top of the boiler, never in the water. Link to a proper Steam Table chart. Steam-Tables.pdf (byworth.co.uk)

Like I said, some people can intuit these things, others can't. A dial gauge is not a tube manometer. It's a stupidly simple idea, if the pressure outside the vessel is lower than inside, the water will rise in the tube above the level in the vessel. Just does. Exactly how a 'swan' barometer works, when atmospheric pressure drops, the water goes up the tube. But if you held a candle under there, it would also go up as the water and trapped air expanded.

[wmgeorge]

Since your an expert, its going to be interesting how you solve this problem.

[mikey553]

Like I said, some people can intuit these things, others can't. A dial gauge is not a tube manometer. It's a stupidly simple idea, if the pressure outside the vessel is lower than inside, the water will rise in the tube above the level in the vessel. Just does. Exactly how a 'swan' barometer works, when atmospheric pressure drops, the water goes up the tube. But if you held a candle under there, it would also go up as the water and trapped air expanded.

Laws of physics are not subject to intuition. If you want to measure the steam pressure inside a boiler, you have to connect a pressure gauge above the water level to be precise in your measurements.

I am not familiar with steam boiler design and do not want to make any comments on how the pressure is measured. But pressure at the bottom of the boiler is higher than the steam pressure. This is due to the weight of water - exactly as wmgeorge said. Try to tell a deep water diver that depth has no affect on pressure. For your information 1 psi = 2.3067 ft of water at 32 deg. F, so the water depth has quite significant affect on pressure.

[wmgeorge]

So if a farmer had a 12 foot high round tank that was sealed completely and put in exactly 10 ft of water, and installed a pressure gauge at the top and bottom.... and added one psi of air pressure at the top of the said tank, what would the gauge at the bottom measure in psi gauge read?

[mikey553]

So if a farmer had a 12 foot high round tank that was sealed completely and put in exactly 10 ft of water, and installed a pressure gauge at the top and bottom.... and added one psi of air pressure at the top of the said tank, what would the gauge at the bottom measure in psi gauge read?

5.3 psi.

[J Tiers]

So if a farmer had a 12 foot high round tank that was sealed completely and put in exactly 10 ft of water, and installed a pressure gauge at the top and bottom.... and added one psi of air pressure at the top of the said tank, what would the gauge at the bottom measure in psi gauge read?

Different kind of gauge, different reading.

The gauge at the bottom is reading inside pressure vs outside pressure. It does not cancel out the water pressure so it reads air pressure PLUS "depth pressure".

The water manometer would just fill with water until it was in balance, with the pipe and the boiler both registering the same height. Now that the "depth pressure" is balanced (canceled) out, the DIFFERENCE between water levels is the "extra" pressure of steam in the system (if any), or in the farmer's tank, the one lb air pressure.

[wmgeorge]

5.3 psi.

Correct!! I wish I had a prize!! A pressure gauge is a pressure gauge! No one uses a manometer on a boiler except on measuring gas pressure.

[J Tiers]

...............A pressure gauge is a pressure gauge! .....................

Not really...... There are many kinds of pressure gauge. Some register pressure above atmospheric. A few measure absolute pressure (vs a vacuum). And a manometer reads DIFFERENTIAL pressure. The DIFFERENCE of pressure at one end vs the other.

Your pressure gauge ....... the one you wanted to out on the tank. What does it read when it is just sitting on the table?

What would it read if you just tossed it into that tank of water and it sank to the bottom?............................. yep, same thing it read on the table. Zero.

Why is that?

Same exact reason why the manometer will read perfectly correctly on the tank of water.

And, speaking of that tank of water...... you seem to be saying that if the manometer was 15 feet tall, and was filled with water to the same height as the tank, that if a tube is run from one side of it to the top of the tank, that it would read WRONG.

That's what you claim, whether you know it or not.

So, let me ask you this. Now we take that manometer, and put half of it inside the tank, sealed up so there are no leaks. We fill that manometer with water to the exact level of the water inside.

When the 1 PSI of pressure is applied, would the difference in water level in that manometer be DIFFERENT FROM the difference in water level between the original manometer that just is connected to the tank, and the water level in the tank?

If so, explain why.

If NOT explain why.

[wmgeorge]

Jerry you are pulling straws out of the haystack, Lets talk real world here, steam pressure gauges are mounted on the top of said boiler. Now if the Homeowner / Expert wants to solve this problem, he needs to go back to the last time it worked correctly and then find out what has changed. All he really needs is perhaps one PSI gauge pressure at the top of the boiler. From my experience working in the real world is more than likely a venting or water issue or at least start there. If might even lead back to the boiler change out.

Edit yes he might need more than 1 psig if he has a very tall house, and yes Jerry I worked in the commercial HVAC world for over 30 years, very familiar with all types of gauges. Never saw a manometer used to measure pressure on a steam boiler however.... in the Real world.

[J Tiers]

It's not done because it is inconvenient, and breakable, NOT because it does not work. It works fine, although reading a dial is a lot more convenient, and you have to make sure the manometer has water in it (automatic if it connects into the boiler below water level).

I'd put a gauge on the top also. My hot water system has a pressure gauge. I like pressure gauges for that sort of application.

Point here is not that a manometer is a great practical idea, but it A) works, and needs no "calibration", and B) the OP has one installed which actually should work just fine if it is installed right.

If his manometer is installed right, and reads zero PSI, then there is zero PSI in the system.

[wmgeorge]

If I was on a service call and suspected the gauge not reading correctly I would pull it off and check the calibration or replace the gauge. Instead of mickey mousing around with something else the Homeowner had. When your charging $80 - $120 an hour the customer expects a professional.

[gellfex]

If I was on a service call and suspected the gauge not reading correctly I would pull it off and check the calibration or replace the gauge. Instead of mickey mousing around with something else the Homeowner had. When your charging $80 - $120 an hour the customer expects a professional.

1st I added a 0-3psi gauge to the 30psi one stock. Nada. Then I flipped open the overpressure release valve. Nothing, no hiss. Then I added the primitive manometer. No pressure. Positively no pressure.

It's definitely not about the venting. Venting is like the rudder of the ship, it's useless if there's no way on her, the pressure. I still think the vanishing gas/BTUs is the key.

[wmgeorge]

So how much water is in the boiler, since your the expert? A low pressure steam boiler has no use for a 0-30 psig gauge. BTW when was the last time this system worked normally? Never on a service call rule out anything!!

[gellfex]

So how much water is in the boiler, since your the expert? A low pressure steam boiler has no use for a 0-30 psig gauge. BTW when was the last time this system worked normally?

The water is up to the normal level, the autofill is operating according to the tech, and it's not using excess water. All steam boilers are required by law to have a 0-30 psi gauge, an additional lower pressure gauge is optional. The boiler seemed to be working after service last March. I'm still puzzled why the tech didn't analyze combustion when that was the 1st thing he did last year.