relief valve working to often ??


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Old 12-01-04, 05:22 AM
minime
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relief valve working to often ??

hey everyone,

i have a bryant hot water radiant heating system, 2 zones if it matters. Now my relief valve i believe (has a pipe running from the top of the furnance down the side of the furnance... a have been putting a cup to catch the overflow that comes out.. the readings of my furnace right when it shut off was 35KPa at 75C.. is this OK ? everyday i have to empty out the cup ..is that too much overflow to be happening??
any takers ...
thanks
 
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Old 12-01-04, 07:01 AM
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I am not used to working in kPa units, but here goes. If I've done my math right, 35 kPa is about 5.1 psig.

Your PRV should be set at 30 psig, so it should not be relieving unless it is defective, or, possibly the system is liquid full. Have you tried shutting off the valve between the boiler and expansion tank, and draining the expansion tank?
 
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Old 12-01-04, 07:25 AM
minime
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no i havent tried that. I am a newbie to this kind of heating, but i am very mechanically inclined, and beleive i could understand it enough to do most repairs...

so this water build-up is increasing the volume, thus increasing the pressure ?
 
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Old 12-01-04, 07:46 AM
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Boy dont know if I have it right are not also. I get not a KPa I come up with a Kgs and at 35 Kgs = 77.179 psi?????
Lets try it this way if it helps. First is the expansion tank empty so the water can expand. If not this can give you the high Psi. like said the PRV is set at 30 psi the auto fill at 15 psi. most of the time we run boilers at 160oF on to 180oF off.
like to know how you make out here.

ED
 
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Old 12-01-04, 07:55 AM
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Originally Posted by minime
no i havent tried that. I am a newbie to this kind of heating, but i am very mechanically inclined, and beleive i could understand it enough to do most repairs...

so this water build-up is increasing the volume, thus increasing the pressure ?
When your boiler heats the water, it expands when it is heated, if your expansion tank is liquid full, there is no place for the water to go, except to release the pressure thru the PRV.

IF, the PRV is not defective, and IF the expansion tank is liquid full, then draining the expansion tank will probably solve your problem. However, you must drain the expansion tank completely, so it is full of air, to allow it to absorb any liquid expansion.
 
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Old 12-01-04, 08:44 AM
minime
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alright, i have two expansion tanks, is that common...?
but i will try what you said rick, and post with what happened...or DIDNT happen..

thanks again..and talk to you soon.
 
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Old 12-02-04, 06:28 AM
minime
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last night i went to empty the expansion tanks, but all they have is a valve on top (like a bicycle tire valve) i pressed it , and some water came out, but should their be something on the bottom of the tanks ? or somewhere below the tanks in the system ?

thanks

mark
 
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Old 12-02-04, 07:53 AM
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If you got water out of the schrader valve, the bladder is ruptured in the expansion tank, and you will need to replace it. You should be able to valve it off, and not have to drain the entire system.
 
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Old 12-02-04, 07:59 AM
minime
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do you know how much one costs ?
 
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Old 12-02-04, 09:48 AM
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Wink

You have to call around for a cost on that bladder tank there. Ask for the same size that you have now in Gal. there is a Extrol and a Fill-trol. Is what we have here.

ED
 
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Old 12-02-04, 09:56 AM
minime
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so let me understand properly....
by the bladder being ruptured, it is causing my relief valve to open due to the pressure increase ?
what is happening in the expansion tank which is increasing my pressure>>?
even better, does anyone have a image, sorta like a section view of a expansion tank... im looking on the net right now,,,
thanks for helping guys.
 
  #12  
Old 12-02-04, 12:49 PM
Wingnut1
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Here's a useful reference:
B&G How Hydronic System Components Really Work

For specifically the expansion tank:
Diaphragm Tank Picture

To summarize: As water heats up it expands and the hydronic system is a closed system. If the water filled the system at 12psi and the water heats up from a minimum of 160F to 180F it must expand while the system volume is relatively fixed. If no expansion is allowed, the system pressure quickly exceeds the relief valve pressure and the system dumps water. To fix this the expansion tank is used. There are a few types, two of which are shown on the above page. Yours sounds like the bottom one because of the Schrader valve on it. If water is coming out of the valve, the bladder must be ruptured. Since the tank is full of water, the expanding water has nowhere to go and thereby increases system pressure until the relief valve blows. Normally the bladder would be pre-charged to meet the system fill pressure (12psi typical), any increase in water temp and thereby volume is absorbed by compressing the air in the tank. The tank should have an isolation valve to allow replacement without draining the system and the pain of re-filling and bleeding the system.

Cheers, Wingnut
 
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Old 12-02-04, 01:18 PM
minime
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you explained that great. I read over those files, it all makes sense now.
thanks everyone for helping me out, and i will post back with my results...
 
 

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