Steam "Piggie"?

[casturbo]

What's the purpose of the pigtail piping on a steam pressure switch? My understanding is to prevent the control from short cycling, but how? Is there some water trapped in it to act as a buffer? Some systems don't have this "piggie", but work OK?

[oil lp man]

The pigtail is a water trap to prevent steam from ruining the control.
Most of the time if there is a problem with cycling, it is caused by a blocked pigtail(from corrosion). Pressure will get between the corrosion in the pigtail and the control and trick the control into thinking the pressure is higher than it is and not allow the burner to come on until the pressure syphons(through the corrosion) back to the boiler on the burners' off cycle. To clean the pigtail I remove it, then use hot water to flush the crud out of the pigtail, then reinstall it. You have to disconnect the wires from the control first to spin it off.
The brass pigtails are less likely to get blocked.
The pressuretrol usually lasts a real long time with the pigtail.
I've never seen a steam boiler without one.
I guess if the pigtail wasn't there all that corrosion from the steam would get inside the control and cause that cycle problem but would be difficult if not impossible to fix.




[Edited by oil lp man on 03-07-2005 at 01:24 PM]

[condenseddave]

They're cheap. I carry three of the 90s and six straights...