Sorry to be such a pest, but I have another question about our aging steam
radiator system in our six-unit apartment building. Last night, an hour or
so after the weekly flushing of the systerm, we heard a very loud knock in
the pipes. As if someone had hit the pipe with a sledgehammer.
Is this dangerous? What should I do? Was the knock, which we heard only
once, probably tied in with the flushing?
probably a steam trap releasing , wouldnt worry about it unless it persists,
9so after the weekly flushing of the systerm, we heard a very loud knock in
4the pipes. As if someone had hit the pipe with a sledgehammer.<PIs this
dangerous? What should I do? Was the knock, which we heard only .once,
probably tied in with the flushing?
Banging steam pipes come from water in the pipes being shot by the flowing
steam. Dangerous? Usually not on a low presure system, certainly on a high
pressure system. The water can be condensate laying in pipes that are not
properly pitched, or it can be "carry over" where the steam picks up water
from the top of the water and carries it into the pipes and slams it into
the fittings at elbows and such. Filling too high can cause that also. I've
seen 12" steam pipe bounce and shake violently from water hammer. It can
also break open or fitting fly off. Try to avoid it.
You may want to consider how you perform the maintenance. Instead of a
weekly flushing, a daily blowdown is peferable. There is no sensible reason
to do a flushing as you are just adding fresh water and all the oxygen it
contains. You want to flush the minerals that condense out by doing a
blowdown of the bottom of the water chamber. If you have a lot of minerals,
a softener would be a big help. Most industrial boilers also have water
treatment to reduce oxygen and scaling of the tubes. Residential cast iron
boilers usually don't do that.
If it continues, get the advice of a professional that knows steam and how
the system works. Get your water tested.
I think that by "flushing" I mean the same thing as you mean in "blowdown."
Daily? No one ever suggested that often before. The guy who installed it
I've never been clear what the "blowdown" does anyway.
OK we are probably talking about the same thing. The frequency depends on
the quality of the water and how much loss you have.
In a perfect system, you'd fill the boiler to the recommended level and
you'd never had a loss and you'd never add water, and you'd never have to
blowdown the system.
reality is, you do have some losses of water or vapor through leaks and
vents so water is added as needed, usually through an automatic valve. As
you add water, you also add dissolved solids that are in the water. When
you make steam, the water is turned into vapor and the solids drop out.
Over time, the solids accumulate and can form a mud on the bottom of the
boiler. This coating inhibits heat transfer, plugs up tubes and other
potential problems depending on the boiler type. So, to get rid of them,
you blowdown (or as you say, flush) out the bottom of the boiler. Some have
a mud drum for that reason. You do this while the boiler is hot, under
pressure, but you don't take the water level down out of the sight glass.
Again, using industrial boilers as an example, the water is checked daily.
We have a meter to tell us what the TDS (total dissolved solids) is and we
do the blowdown accordingly. In our case, this is a process boiler and we
use up to 10,000 gallons of water a day for steam so a lot of stuff can be
left behind. We also add chemicals as I noted before to assist in keeping
the insides clean, keeping the solids dispersed, and driving off oxygen.
You may have radiators not pitched to drain the water if you have
removed them to refinish floors or paint, or the building settled,
just check they angle, a shim or wood can be used to raise one end. In
blowdown I do the low water shutoff and a drain at the bottom of the
boiler for about 5 seconds maybe every week or 2 if it continues and
you are not overfull maybe the building has settled changing the pitch
of a pipe.
In short, everything from the radiators to the boiler has to have the
radiators and piping with a slight pitch back to the boiler. This
includes all of the piping. Even that hidden in walls and floors. Not
always the easiest of fun jobs.
A bad steam trap at the radiator or in the lines can cause this
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