Steam system disaster...

Jeremy Scott

So I am looking to save energy in this school building in MA. Built in 1905 and uses a ton of gas. First, as I posted about previously, this building has thermal chimneys for ventilation. Steam radiators in multiple flues, one per classroom, induce air to rise out of the chimney, thus providing ventilation to the space. Luckily we found the steam supply's were cut long ago, but the chimneys are still open as well as the classroom vents.

Next, the custodians complain of water hammer. When asked if the traps have ever been replaced they said they never had a reason to. Hmmm, classic response from someone who has no clue. Here is what we found. Each classroom has the original steam radiator and a newer unit ventilator. Pneumatic control valves on the UVs and TRVs and traps on the 2-pipe radiators. In the boiler room is where the fun begins. Replacement condensate receiver was piped so that their is now a water leg. We couldn't find any vents in the system but they are getting heat so we assume the steam is passing through the traps and pushing the condensate through. Our assumption is backed up by the fact that the receiver vent has an F&T trap installed at the top of the vent with a garden hose connected to the trap outlet and run to the drain...second they extended the condensate line to the boiler feed tank (not the pumped return from the receiver), but put an F&T trap on that line as well before it goes into the tank...the vent for the boiler feed has one flexible plastic tube directed to the floor where condensate is leaking out and another plastic tube feed to the outside where steam is pouring out. They said they typically have ice on the outside wall above the vent...so I guess there really was no reason to suspect the traps have failed...one other nugget, the relief vent connection at the rear of the boilers was extended for surface blowdown, i guess, but it is capped and an F&T trap was installed and piped back to the boiler feed tank...still trying to figure out the idea behind that trap.
Jeremy

Brad White_202

So much room for improvement

where does one begin? I have to wonder at what pressure they operate. The F&T vent head sounds like they had enough pressure to lift and blow... That hose sure fixed that.

The relief valve connection has some concern. I assume that the path to the relief valve is unrestricted but I would also think that the relief valve would be higher in the steam chest than at the surface.

What you describe as a surface blowdown, that one which has the trap? It is more likely a surface equalizer, used when multiple low pressure boilers are piped in parallel. If the boiler feed fails open, the traps prevent a flood and forms a high limit water level control function. Usually this is an inch or two above the normal highest operating water level.

When I think "surface blowdown", I think of a manual skim tapping. Maybe we are thinking of the same thing.

Jeremy Scott

the pressuretrols were weird...the boiler that was running was cycling between 2 and 4 psi though it was set at .5 and .5...the boiler that was manually turned off was set for 2 and 4. go figure...

pipe to relief is unrestricted. they extended the pipe after the relief valve and added the trap.

i was thinking the same as you on the skimming. From what I understand this is usually done from the vent tap.

Brad White_203

I suspect

that the instrumentation piping (gauge and pressuretrol piping) is clogged and not responding at least until the pressure forces the gunk to move a bit.

We do agree on the surface tapping, often it is a lower one with the relief valve coming off the top, but some manufacturers do recommend it the way you describe, a tee holding the relief valve.

When I do "waterline maintenance" I tend to place the trap off of the equalizer (and like my equalizers large for this reason).