Vacuum Vents

George3

I have recently purchased an old house with a 2 pipe steam system. Most of the convector's steam traps were bad so I am replacing them now. While doing this I wanted to make sure that the main vents at the end of the mains and the dry return lines are functioning. They look pretty old especially the on eat the end of the main line - Hoffman 16A. I was surprised to see that both main vents are vacuum vents Hoffman 76 and Hoffman 16A. This tells me that the system originally probably was meant to run as a Vacuum system. The boiler and the near boiler piping and parts were replaced probably 20 years ago. I don't see a vacuum pump currently either.

Can someone please help me with the advise if it is better to try and to restore the system to run on Vacuum by adding vacuum pump etc. or just replace the Existing vents with a non-vacuum ones and run the system as a normal 2 pipe one.   

Jamie Hall

The presence of

vacuum vents does not, repeat not, indicate that the system was originally intended to have a vacuum pump or something of that sort.  Much much more likely that it was a vapour system -- which is not quite the same as a "normal" two pipe system.  The vacuum vents simply allowed the system pressure to drop below atmospheric as the fire in the original coal furnace died down, increasing the length of time the system would heat on a load of coal and, to a certain extent, the efficiency (which was horrible anyway, but that's another story).



Your best bet is to replace the vacuum vents with Gorton #2s -- they might even just screw right in -- for starters.  And figure out what kind of vapour system it was.  And set your pressure down; if you have a pressuretrol, set it as low as it will go reliably.  If you are blessed with a vaporstat, a good starting point is around 8 ounces cutout and 2 ounces cutin.