What is the safety zone in PSI for boiler pressure (and temp if important) for hot water Boiler heat

NassauTom

Icesailor, believe me, I had never seen anything like this nor did I think it possible. It has been a very unpleasant eye-opening, to put it mildly. The expansion tank had definitely failed and I am fairly sure that the pressure reducing valve integrated into the Extrol tank had also failed. But it was the fact that the pressure relief valve was also bad (rusted shut) that led to the hat trick necessary to cause this type of failure. Apparently, when the oil company comes out to do annual service on the burner and boiler, they don't look at any of this. SURPRISE!!!! Well, I've learned a lot about my heating system due to this and I'll be better armed to maintain my system myself.

NassauTom

The thing to think about is that these radiators are 100 or more years old. They have been through 100 or more heating seasons and may have been exposed to less than optimal treatment at various times during their lifespan. In fact, the house was vacant before we bought it 10 years ago.

Bottom line is that the cast iron was likely stressed and likely had developed weak spots which were the points of failure when they exposed to higher than normal pressure. We all think of cast iron as brittle but it does deform a bit before failing (see the stress-strain diagram attached). The same radiators would not have failed under the same conditions 100 years ago. At least, that is my conjecture.

icesailor

As far as I know, there is no ASME approved 30# pressure relief valve incorporated with that bad idea of a tank/fill valve fitting. The only true safety pressure relief is installed on the boiler. Hydraulic shock can do that with a failed compression or bladder tank. When the water is cold and the system has to heat up, with no place to go, the pressure will build to astronomical levels. Enough to split old cast iron radiators. The cast iron composition of the old radiators wasn't as standardized as much as it is today.

Too bad no one flipped the test lever on the PR valve and saw that it didn't work. Of course, if it was leaking after the test, some crabby customer might accuse someone of screwing with their system just to sell them a new valve.

icesailor

All of us have worked for them.

And some of their type come here and start crabbing about how someone was trying to rip them off because they changed a PRV that wasn't leaking (but they neglect to mention that it was hard to find because it was covered in rust).

NassauTom

I think a lot of that crabbiness comes from ignorance. Honestly, I might have been one of those crabby customers because before this all happened, I knew nothing. Once you understand the system a little bit, you appreciate its complexity, the importance of well maintained components, and the work and cost involved in maintaining it. I was an ignorant homeowner who didn't even know enough to check that the pressure relief valve was working. I sure as hell know to check it now!!!

NassauTom

Hatterasguy said:

I am a bit surprised that one of them could withstand 100 psi without discharge. It's just a rubber diaphragm and a spring. How is it possible for the rubber to hold that kind of pressure?

A LOT of rust. I'll try to take a picture of it and post it later.

If you have any customers who don't want to spring (no pun intended) for the cost of a replacement PRV, now you have a real life story you can relay to help explain to them why it is such a good idea to do.

icesailor

Hatterasguy said:

I am a bit surprised that one of them could withstand 100 psi without discharge. It's just a rubber diaphragm and a spring. How is it possible for the rubber to hold that kind of pressure?

???

The system water goes in the diaphragm bag. The air pressure is outside the shell, against the rubber diaphragm. If the diaphragm leaks the water into the air side, or the air leaks out, there is absolutely no place for the pressure to go. When you unscrew a #30 Extrol that is full of water because it failed, you better have made allowances for when it comes free from the last thread. And have your foot out of the way.

NassauTom

Hatterasguy said:

NassauTom said:

A LOT of rust. I'll try to take a picture of it and post it later.

If you have any customers who don't want to spring (no pun intended) for the cost of a replacement PRV, now you have a real life story you can relay to help explain to them why it is such a good idea to do.

It can be completely encased in rust. Inside the valve is a spring and a rubber diaphragm. If the pressure exceeds 30psi, the rubber lifts off the seat.

I suppose that it's possible that it cannot lift if the entire spring assembly and internal housing for the spring is completely corroded. But, since they are usually made from brass, it's a bit unlikely.

Here is a pic of the old PRV. It would not open when pulling on the level. If I had pulled any harder on the lever, I would have broken it off.

icesailor

Sorry, but the most common replacement boiler PRV is a Watts #340 30# PRV. It has a Cast Iron body with a brass seat. The spring is steel. The escaping water vapors can cause the spring to rust. The rust can collect on the spring to the point that the spring can not work.

Some of us here have seen the lengths that some homeowners will go to avoid being "ripped off" by what they consider to be unscrupulous service technicians. So, they might cut the copper drain on the valve off so they can unscrew the adapter and put a 3/4" black plug in the relief valve drain. There is one small place to leak left where the stem on the spring goes through the cast iron of the valve body. To stop the leak, they use Epoxy Patch stop leak in a tube.

Or why you aren't supposed to leave a threaded end on a relief valve drain pipe. So someone doesn't screw a cap on it to stop it from dripping water on the floor.

What is scarier is if the boiler was hot, over 212 degrees, and those radiators "exploded". The boiler would have too with catastrophic consequences.

NassauTom

When you unscrew a #30 Extrol that is full of water because it failed, you better have made allowances for when it comes free from the last thread. And have your foot out of the way.

Exactly! Luckily I did think about that and was prepared for the weight of it when it unscrewed from the last thread.

NassauTom

icesailor said:

What is scarier is if the boiler was hot, over 212 degrees, and those radiators "exploded". The boiler would have too with catastrophic consequences.

I consider myself VERY lucky that only the radiators cracked and not the boiler.

RobG

I would bet that at some point in the past the rads in the home froze up causing stress fractures. The fractures had sealed with rust then the small overpressure was the proverbial straw that broke the radiators back.

icesailor

"" Thanks for that photo.

It appears that the valve is exactly the opposite of your Watts valve, Ice.

The body is clearly brass, but the excessive corrosion around the seat would imply iron in there. The spring is reasonably intact and would not have impeded the action of the valve if the seat wasn't "welded".

If that seat was brass, the valve would have functioned as designed. ""

Do you ever read for comprehension what I write and say?

I said that the most common PRV used is a Watts 3/4" #340 cast iron body with a brass seat. I didn't say anything about the POS cheapest available/bought in bulk PRV, with that Male Thread Conbraco 3/4" PRV that so many boilers come through with.

When I installed boilers, I always swapped the FPT inlet for a Watts #340, because when and if I had to change one. I wouldn't be carrying around THAT valve. I always piped the drain with nipples and the long drop piece with the end of the copper tube annealed and the adapter so I could be sure to get it nice and plumb. No heading out to the truck for the flamethrower torch and fittings to change the relief valve. And for some of us who are thorough and nosey, we take the pipe and nipples off and have a look see at the seat to see if it is leaking bye. Especially if we see a rust spot on the floor under the overflow drain or a bucket under the drain.

Years ago, I went to check a house that a caretaker had "just checked". It had snowed 5 days before. My tracks were the first ones to the house. For anyone not having the experience, there is no sound of quiet like the quiet sound of a big house that the heat has gone off. And the temperature inside is as cold as a witches heart. You go into the kitchen and try the faucets, The faucets are frozen solid. Every sense is at attention. What to do now. Why is the heat off. Fire off the boiler and try to warm it up?

When suddenly, there is a loud BANG from upstairs. Scares the crap out of you. Like someone took a 10# top mall and hit a pipe behind you. Dead silence. You go to explore. BANG!!!! Another bang. The radiator in the hall just blew out the top end, and it went right through the wall where you are now standing. Good thing you weren't standing there.

And the owner believes the caretaker that he was " just there" so the caretaker hires someone else to fix the problem and broken pipes.

The problem was caused by the oil running out, the Caretaker was vacationing in somewhere in the Grenadines, and the oil company had tried to deliver oil but found the tank empty and couldn't contact the contact person the caretaker left. He no longer worked for the caretaker. Life in the Fast Lane.

I don't miss the lying caretakers.

NassauTom

RobG said:

I would bet that at some point in the past the rads in the home froze up causing stress fractures. The fractures had sealed with rust then the small overpressure was the proverbial straw that broke the radiators back.

Rob, I believe (and fear) that you may be right. Which would mean, of course, that there may be more stress fractures lurking, especially in the radiators that have not yet failed.

Assuming I make it through the winter with no further dramatics, this spring it may be worthwhile to remove each radiator in the house and pressure test it.

icesailor

In almost 50 years of looking at frozen and broken pipes, if a radiator freezes, it doesn't always crack. If it cracks, it leaks. Every time. Old Victorian column radiators are a thinner casting and a poor quality of cast iron. They usually split along seams or pointed places. Because there is a lot of water to freeze and expand. Modern column type radiators don't have the water volume in the tubes to exert enough pressure to split the Cast Iron. That's why you often see the end sections with blown out top section pieces. More accumulated water.

Live dangerously. Test it now. Get a small air compressor for nail guns with a secondary pressure regulator. Set it for 28#. Make something so you can connect an air hose to the compressor, with the other end connected to the boiler. Drain the water out of the heating system. Close all drains, air vents and automatic air vents. Fill the system with air. When the system gets to 28#, the compressor will stop. Shut off all air connections to the boiler so it is isolated. If you have normal hearing that hasn't been destroyed by listening to loud music with loud bass, or going to Grateful Dead concerts, you will hear any air leaking. If you have any children that haven't yet damaged their hearing, try them. If the pressure is still 28# after an hour, you don't have any leaks.

Yours didn't freeze up. They broke because of a defective PRV and a failed bladder tank.

Harvey Ramer

I personally think that those FillTrols are the devil. When I do a boiler service, one of the items is servicing the expansion tank. With the FillTrol you have to remove the tank from the system and you can't do it without getting wet. I also discovered that the stem in the top of the tank has a habit of getting tight. When that happens the valve will keep on letting water in the system till the relief valve blows.

They are just so darned unhandy. Don't like them a bit.

icesailor

A really bad idea to cut something out of the food chain.

NassauTom

nicholas bonham-carter said:

What a loss to lose such pretty rads!
glad you were able to get the cause under control.--NBC

I won't be losing the radiators, just the cracked sections. I have another radiator made of the same segments and will be taking the damaged radiators apart, removing the cracked sections and then installing sections that I will take out of the sacrifice radiator.

NassauTom

icesailor said:

Sorry, but the most common replacement boiler PRV is a Watts #340 30# PRV. It has a Cast Iron body with a brass seat. The spring is steel. The escaping water vapors can cause the spring to rust. The rust can collect on the spring to the point that the spring can not work.

The PRV that failed due to a large buildup of rust fusing the disk to the seat was a Watts M330-M1. The valve body is brass. Due to all the corrosion, I can't tell what the other components are made of.

SWEI

NassauTom said:

The PRV that failed due to a large buildup of rust fusing the disk to the seat was a Watts M330-M1. The valve body is brass. Due to all the corrosion, I can't tell what the other components are made of.

How old was it?

NassauTom

SWEI, I don't know. I know it is more than 10 years old (we bought the house 10 years ago).

SWEI

At this point, it sure doesn't owe you anything.

NassauTom

SWEI said:

At this point, it sure doesn't owe you anything.

Except 3 radiators. LOL