Pressure Relief Valve Leaks

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  #1  
Old 11-24-04, 08:41 PM
SteveM
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Pressure Relief Valve Leaks

I have a Dunkirk, 225K btu closed system gas boiler with a new B&G NRF-22 circulator and a B&G 12 psi pressure reducer. There is a Honeywell Aquastat. The expansion tank (x-tank) is a Flair #30 (4.4 gal) , bladder type, 12 psi factory setting, Max. 45 psi. There are no air scoops.

The PRV oozes at about 28 psi. I am 95% sure it is due to an undersized x-tank. I performed a few tests on the existing x-tank and I feel its is working well with its given capacity. I am considering replacing the x-tank with a #60 or a #90 since I have cast iron radiators throughout.

The PRV started oozing for the first time this season (I think) because I had performed work on the system every year (adding air to the system on drain and refill). Also, I removed a few vertical, unused, capped pipes which likely added air cushioning to the system. Also, I regularly bleed the radiators so I feel the system is pretty air free.

I read a few threads here and I see an option of "adding air" to the system. I thought I might accomplish this by turning off the water supply and draining a little water (during high pressure operation) via the return side mounted sill**** until the pressure drops. Then turning the water supply back on to provide steady pressure (?)

I am concerned about adding air blockages to the system and reducing system heat efficiency.

What do you think ?

Also, The system is installed in a 2 story house in Chicago, IL. What is the best hot operating pressure range ? And what is the best hi lim setting for the aquastat in Chicago. 140 F ? 160 ? 180 ?

Thanks.

SteveM
 
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  #2  
Old 11-25-04, 04:40 AM
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First of all, I would never add air to a heating system for any reason at all. It causes corrosion and needs to be removed from a system as soon as possible after start up. You may have a bad expansion tank and never knew it because of your other air cushions in the system. Take pressure off the system and check the pressure in the expansion tank. It should be around 12 psi.

If that shows up OK, then you could isolate the feed valve and see if pressure still rises. If not, replace the feed valve.

The expansion tank may be undersized too which is hard to calculate.

I think 180 degrees would be a good place to start with the high limit.

Ken
 
  #3  
Old 12-11-04, 08:27 PM
SteveM
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PRV blows at about 30 psi

I added a new #60 x-tank to the system and left the existing #30 x-tank installed. I located the new x-tank on the same supply (hot) pipe about 2 feet from the existing x-tank. That roughly doubled my expansion capacity. Many of my pipes are the old (large) gravity feed type. Plus, I have 15 cast iron radiators. Lots of water in this system

I also added an air scoop and an air vent. The added x-tank is installed on the bottom of the air scoop with the air vent on top.

Its working much better now. No blown PRV. The pressure is still a bit high (about 26 psi) but that occurs at a much higher temp so it should work just fine. Thanks.

What is a good pressure range for a hydronic boiler ?

What is a good exhaust air temp range measured about 1 foot above the boiler ?

Is there a way to capture at least some of that exhaust heat ?
What a waste of btu's and $$$.

SteveM
 
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Old 12-12-04, 05:30 AM
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26psi is a little high. It would be best for a 2 story house to run around 15. If the expansion tank is working, the pressure shouldn't rise too much between hot and cold.

The minimum stack temp for a masonry or tile lined chimney is around 350. If you have less than that, you will have condensation problems inside the chimney and it will degrade in only a few years. An acceptable temperature is anything between 350 and about 650. Anything over 700 is a little excessive. The devices to reclaim some of that heat are not cheap, they reduce the draft at the boiler and they require electricity to run a fan. The real question is how long until they pay back. I think it would take many years for a heat reclaimer to save its cost.

Ken
 
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Old 12-12-04, 10:04 AM
SteveM
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Best method for measuring stack temp

Ken:

Thanks.

What is the best method for measuring flue temp?

I have a device that attaches magnetically to the outside of the ductwork (I located it about 1 foot above the boiler). It has a range of 0 to 850 deg F with 25/50 deg F increments. It is used on wood stoves to help avoid chimney fires from accumulated combustibles in the chimney stack.

I am not convinced it it is the best method.

SteveM
 
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Old 12-12-04, 01:21 PM
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I don't know what is available besides what we use. Ours is made to go in a small hole and reads up to 1000 degrees F. Most newer voltmeters have a thermocouple you can add that gives you digital accurate readout of temps. You also didn't say what your temp was. I don't think the magnetic ones are quite as accurate as you might want. It will put you in the ballpark though.

Ken
 
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Old 12-12-04, 06:26 PM
SteveM
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Chimney stack temp...

Ken:

The magnetic thermometer currently reads about 275 deg F. Thats low from what you stated earlier. How do you increase flue temp ? A new boiler ?

On the pressure build up, I have done the following:

1.) Added an additional #60 x-tank to the existing #30.

2.) Filled the system with water via the reducer valve and checked cold system pressure. It read about 13 psi. Looks like the reducer is doing its job.

3.) Shut off the water supply prior to to start up ("good practice" per the B&G rep engineer I talked to). Start up with the water on can increase the cold start system pressure and supply continous water to a leak.

4.) Checked the x-tanks for operation. Both felt warm in the upper 20-30% at peak temp and pressure. They seem to be working - but how well (?)

5.) Observed the pressure rose steadily from start up to peak.

6.) The new B&G NRF-22 circulator is located (as was the old circulator) on the return side of the boiler. Again, the same B&G rep engineer said that actually may help the pressure build up a bit. He also mentioned that the circulator has little to do with pressure build up as long as the radiators are getting hot and you are "comfortable".

7.) Also, I performed a test. I ran the system to hot then shut off the gas supply. I ran the circulator a few minutes then shut off the entire system. The pressure held steady while the system temp rose a bit from the accumlated boiler heat.

What else can I do ?

SteveM
 
  #8  
Old 12-20-04, 11:40 AM
SteveM
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Tankless Coil Boiler

Ken,

I looked at the inside my Dunkirk Boiler and observed what appeared to be coils. Are these coils part of a tankless design ? Can a tankless design cause pressure problems if the the boiler has a leak ?

Also, I tested the magnetically mounted temp gauge on another (new) boiler system. I am returning the gauge to the vendor. I do not believe it will accurately measure AIR temp of the boiler vent. Looking for a local supplier.

SteveM
 
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