Vaporstat setting

JoeyQ

Hello I am reading "the lost art of steam heat" and have a question regarding the cutout of the vaporstat. The rule for cut in is no less than twice the system pressure drop. He works it out in psig so 4 ounce total is made 8 ounces to ensure pressure drop is overcome. Then the 1psig is added to give us the 215 deg steam at the radiator so we define edr. So cutout is at 1 1/2 psig. Perfectly clear on that. With vaporstat the cut in setting is 4 ounce. The book days the cutout is ten ounces. My question is where does that number come from? I know that the 4 ounce is double pressure drop for the system. But the 10 ounce cut off value makes no sense to me. I take it the vaporstat is more sensitive than the pressuretrol. Is their a formula behind this cutout value or did they just pick it based on a safe assumption ?h