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13 Aug 2001 at 2:32 am #275168MasterPlumbersKeymaster
I just replaced a radiator and when I refilled the system I could not get the 2 large radiators on the second floor to fill, I got some air then nothing, what gives? I got the circulator to run but that didn’t make a difference either
13 Aug 2001 at 4:10 pm #291287SylvanLMPParticipant
What you need to know and do is the following.
Most boiler manufactures that include an automatic feeder set the pressure at 12 PSI with a maximum setting of normally 20 PSI. Depending on the actual maximum working pressure of the boiler as some hot water boilers I work on have a 160 PSI rating.
What you need to do is locate your pressure and temperature gauge and this TRI indicator gauge will also show you altitude.
You should see a red line where the 30 PSI ends and the normally pressure/altitude setting is.
How heating folks set this is by filling the system COLD and watching the gauge.
Then we know the following the height exerting a no flow hydrostatic pressure reading will be calculated as follows.
Height pressure (.434) will give a hydrostatic reading.
Now we know the min of pressure this system requires to operate.
We then add about 8-10 PSI to over come friction losses and to make sure we have a positive pressure to keep air out of the system.
To find out how much pressure you actually need you can measure from the highest radiator to the top of your boiler and times this by . 434
Then you can adjust your pressure setting accordingly.
To find the actual pressure required take 2.31 times the pressure and this will tell you how high the water will be elevated.
Remember that as water is heated it expands and creates more pressure and this is why you have to make sure your expansion tank is working and properly sized.
On your automatic feeder you will see a handle for Quick fill, lift this handle when the boiler is COLD as so not to thermo shock the boiler and cause a possible boiler crack.
Watch the pressure gauge while fast filling and stop just below the 30 PSI mark
UNLESS you want to test the relief valve at this time which should be tested yearly then just watch the gauge and see exactly when the relief valve discharges.
Now once you have the pressure up then you can go ahead and bleed out more air until you get a full stream of water.
Then you can again check the pressure and adjust accordingly.
You may want to install an automatic air bleeder like a Bronze Hoffman # 75 or Bronze Spiroflex air eliminator that removes micro bubbles from the system.
Any questions please feel free to E mail me.
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