Posted by Harold Kestenholz - Hydronic Network on May 19, 2001 at 14:29:07:
In Reply to: trapped air posted by harvey lankford on May 19, 2001 at 11:29:22:
Gases will go in and out of solution and gases can leave the radiation over time from properly located automatic air vents. As the system is 60 years old, it is more likely an air control system, not an air elimination system. The main difference is that the air control system tries to return the gases to a bladderless tank near the boiler. This means that there must be a flow of water above 2 fps to move bubbles of water within the radiation. In other words, the air control system usually traps air in radiation and must be manually vented. A useful procedure is to have a cabinetmaker install doors near the vents to permit their use.
An air elimination system would include automatic air vents at the radiation and a bladder-type tank.
An older gravity system would have an open tank in the attic or high closet and the water velocity would never be high enough to permit automatic venting.
Just a note - if the system really registers 30 psig on the gauge, you have a dangerous condition. If the pressure does not exceed 25 psig during the coldest days of the year, the system is functioning. Check the accuracy of the pressure gauge and the operation of the pressure relief valve, they do need to be replaced periodically.
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