Re: Loud hissing from steam radiator's air valve

On Jan 1, 3:17 pm, mathneuro <mathne...@xxxxxxxxx> wrote:
Hello,

I have a one pipe steam radiator system in my condo unit that lets
pressure out through the side air valve. There is no banging or
clanking, but there is an abnormally loud hissing noise from time to
time that's very disturbing. Upon visual inspection of the air valve,
I cannot for my life determine where the release hole is, which is
very curious. (My intention was to make sure that it was not
obstructed.) It is not painted over, either. Any suggestions on how to
solve this annoying problem economically would be greatly appreciated!

Cheers,
J

I am a power engineer fourth class and until I retired a few years
ago, I operated steam boilers in several buildings which all had two-
pipe systems. With the one-pipe system, the steam supply line would
be relatively short, and the pipe graded carefully so that the
condensate all drains by gravity back to the boiler. I am not
familiar with the "side air vent" as you call it, but normally very
little air would need to be expelled from a steam system. The fact
that lots of air needs to be expelled periodically means that
corrosion is taking place in the system. Heat plus carbon dioxide (in
the air) plus water equals carbonic acid, which corrodes iron (not
good).
The fix for the problem is probably in adjusting the controls.
Perhaps the boiler is being operated by a computer that allows the
system pressure to drop to zero for a set time, then re-starts the
boiler. When the pressure drops to zero, air is sucked into the
system maybe at the radiator vent. When the boiler cycles On again,
the air goes hissing out again at the radiator vent until the steam
hits the vent and shuts it. If there's a computer operating the
boiler, its not controlling it right.
On top of the boiler, see one or more safety relief valves that
will release if the pressure were ever to get to 14 psi. There should
be an inspection certificate on the wall nearby showing when the
boiler needs to be overhauled and inspected again. This is every 2
years for a low-pressure boiler unless the inspector finds an
unacceptable amount of corrosion happening.
On the side of the boiler, see the High Limit control, which
should shut off the boiler if the pressure were ever to get up to 13
psi. The High Limit is a box maybe 4" wide and 3" high with a clear
plastic front. There's an adjustment screw on it: Turning the screw
"In" will "Increase" the setting at which the control will shut down
the boiler. On the top of the control, see a reset button which needs
to be pressed or the boiler will not start again.
Next to the High Limit, see the Operating Limit, which is a box of
the same size, but it has two adjustment screws on it. The bigger
screw determines the point at which the boiler will shut off in normal
operation. This "Off" pressure is typically 12 psi. The smaller
screw determines the differential, that is, the point at which the
boiler will start up again. The "On" pressure is typically 9 or 10
psi.
Somewhere in a typical system, there is a low pressure alarm. If
the pressure were to drop to 8 psi, an alarm would alert Security, who
would then phone whoever is On-Call (poor bloke like me).
Adjusting these controls should be done by someone who is familiar
with them, but if you do it yourself, make sure you know where the
toggle switch is on the front of the boiler so that you can manually
shut it off if you're getting befuddled with the controls. Near the
toggle switch is a dial which controls the rate of firing. Adjust the
rate of firing to the bottom end of the scale so that the pressure
climbs only slowly while you're adjusting the controls.
If air is excluded from the boiler and piping as much as possible,
and if the boiler water is appropriately treated with chemicals, your
boiler will serve you well for many decades.
If you have any other questions, I'd be glad to try to answer
them.
Sincerely, Brian
.