steam/no pressure

steam/no pressure buildup

Hi guys,
With your help and the Lost Art, I'm slowly getting my one pipe to work like it should! After venting the mains, unplugging the pigtail, cleaning the low water probe, and installing a 3# gauge, I have another question. Boiler was hot, jumped the thermostat, fired for 30 min, and only saw about .5 psi from initial fire till I shut it down. Rads were hot. Pressuretrol at .5 to 1.5, mercury limit at 3.
Does this mean some of the main or radiator vents are not closing, and it can't build pressure? When they fail is it in the open state? If a tenant has removed a vent will that cause this?
Thanks for sharing your years of experience.
Lance

net steam production

Lance, my system behaves the same way. 6 oz almost instantly after ignition and stays there for 30+ minutes. Then the pressure begins to build again, going from 6 to 11 in about 3 minutes. My vaporstat cuts out at 11 oz. I know from the days when my pigtail was clogged the pressure can go a lot higher. I think if a vent is not closed at 0.5 psi you will hear it hissing.

My hypothesis for my own system (which is sized just right for the connected radiation) is that while the system is heating there is a near balance between steam production and condensation that keeps the pressure flat for a long period. When all the iron is finally up to temperature the steam cannot give more heat to it without being at a higher pressure and so it starts to rise again. This is the ideal preassure at which to cut out I would imagine.

If this is correct then your system fills at about 0.5 psi, and ideally you'd want to cut out just above that level, something you can't do with a pressuretrol.

Bottom line is if you don't have hissing vents and the house is comfy everything is OK, but you could save some money cutting out earlier with a vaporstat.

Vent in rad upstairs

Lance,

You post sounds like it a tenant property, and you are not sure if all of the vents are in place.

You MUST have all of the vents in the rads when the system is making steam. If they are not, it could discharge a LOT of steam into the room. That much steam in an unoccupied apartment (people not home) could cause significant damage. If they were home, and let’s say they were sleeping when the boiler fires, it could really hurt someone if they were near the vent FPT on the rad when the steam discharges.

When you are testing such a system, you must have access to the entire system and all of its components. Don't assume that all is well upstairs, or you could really have a problem.

Ed Carey

steam/no pressure buildup

Thank you all for your input and safety alerts. I will be sure to check all vents are in place. Previously several large (60-72" long) radiators were run with no vent, and never emitted steam. now with the varivalves they seem to be heating further across.
I haven't observed a complete boiler cycle since installing the 3# gauge, but yesterday it was not zero'd, and was straight down off the scale when firing. Is it shot, or can I readjust to zero? Hope my new gauge isn't toast! Thanks
Lance

Thanks Rod,
Yes, the gauge is on a pigtail, which was cleaned and filled with water before use. The 30# was clogged and never has moved. I zero'd the 3# today and it seems to be ok. Thanks to all
Lance