Stop getting sicker
Air Purge Index
Fill the system to the minimum pressure
required to keep the system filled to the top.
Make sure the pressure in the system is high enough to force air out of the system; or when
you purge air, it will come back in again.
· You are going to establish the
minimum cold fill pressure (static pressure.)
· If the expansion tank is an older
tank without a bladder the tank will be filled to the minimum
pressure by the pressure of the system.
Shut the tank off from the system. Drain the
tank completely. Close the drain fitting. Open the valve to the system. Fill
the system so water will come out of the highest part of the sealed circuit.
· Add four more pounds of water pressure
to the system by adjusting the pressure
reducing valve higher with the knob
or screw at the top of the regulator or by adding water through a hose
from the cold water line through a hose to a system fill valve.. This is
the lowest
pressure you can permit in the system.
Lower pressure will permit air to come back into the system through open vents.
By
adding four more pounds than the pressure required to fill the system to
the top, the expansion tank will be charged with extra water
to make up for variations in temperature. This is the pressure setting
for the
pressure
reducing
valve.
· The pressure
reducing valve will be set to this pressure of minimum height plus
four pounds.
If the pressure reducing valve is set higher than this pressure, the expansion
tank can act as if it were too small by being overfilled.
Often, 12 psig
takes care of a two-story house; although, as you can see, as not all houses
have the highest part of the system at the same height, this can vary depending
upon the height of the top of the highest
radiation above the boiler gauge.
Mark the boiler pressure gauge with the
pressure. If
pressure drops below this mark, the system must be repaired and refilled.
If a bladder-type expansion
tank:
Set the minimum pressure while the diaphragm tank
is not on the system or the system does not contain water.
Estimate
the height of the highest radiation in the system above the boiler. Divide
that height number in half, that number
is the pressure in pounds that you will use to adjust the bladder-type expansion
tank air pressure.
· You can add air to the expansion
tank through the stem with a hand tire pump or you can release
air as if releasing air from a tire.
By then adding four more pounds to the
system (above the pressure required to fill the system to the top, which
is the pressure
used
to fill the bladder with air) the extra water forced into the tank will
make up for variations in temperature. This
is the pressure setting for the pressure reducing valve.
· Shutting the cold water feed hand
valve after service permits the use of the pressure gauge
to detect leaks and prevents damage to the home by leaks from the system.
· If there is concern that a serviceperson must return to refill the system after adjusting the pressure properly due to air leaving through automatic vents, the serviceperson may charge the system to 20 psig so there will be a reserve of extra water in the expansion tank to make up the difference. A small amount of extra water may dump out of the relief valve during cold weather until there is no excess water in the system.
NOTE: The minimum fill pressure is not the pressure the system will run at when the water in the system becomes warm. As water heats, it expands, so the pressure will be higher than the minimum. The pressure should not be higher than 25 psig in the coldest part of the year or the relief valve can lift, dumping water. After water is dumped, the pressure when the water cools may be less than the minimum pressure.
NOTE: If the expansion tank is left at the usual factory pressure of 15 psig, the pressure reducing valve is set by the factory at 12 psig, and the system requires 12 or less psig to make the minimum fill pressure plus 4 psig, the pressure will move up to 15 psig as soon as the system starts heating. There will be no extra reserve of water in the expansion tank to make up for air leaving from air vents. So there may be noise in the radiation from free air bubbles passing through as the system cools even though the system had been purged well
