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Insulation changes everything

JUGHNE Member Posts: 10,779
In the process of adding 1" FG to steam piping. (Never had insulation) Two 3" mains are 113' & 107'.  Mains are 85% done.  One 2" return is 80% done.  System used to run 3 to 7 ounces pressure and only cycle with T-stat.  Now pushing 1 lb pressure.  Finding several leaks (rad bonnets/unions etc. that never were there before).  The pressure control is set down all the way; screw ready to fall out.  I know it is worthless for this system but never needed one until now.  So is it obviously time for a vapor stat control?   One note when pressure is up to 1 lb and power switched off a vacuum is reached in 6 minutes (twisting a 32 oz gauge needle around past 0 up to the "32" number at least.  Compound gauge might be on 1" HG).  28 minutes later we are back up to 0 psi.  Power on and 28 minutes later we are at 3 ounces.  Is there any to use this vacuum to still heat or have I not read Dan's books enough?    Each main has a Gorton 2 & a Hoffman 75  (more to be added later) rads have Hoffman 40 & some 1A.  Any thoughts appreciated.