When fuel oil is subjected to a vacuum in excess of how many inches of Hg does it start to come apart?

When fuel oil is subjected to a vacuum exceeding 15 inches of mercury (Hg), it begins to break down. This is primarily because the vapor pressure of the fuel oil is such that as the pressure decreases, the liquid can start to boil or vaporize, leading to the formation of bubbles and eventually causing the liquid to separate into its components. The phenomenon is commonly referred to as cavitation, which can cause issues in fuel delivery systems, leading to a loss of fuel efficiency and potential damage to the system.

Understanding the behavior of fuel oils under vacuum conditions is crucial for those working in HVAC systems, as excessive vacuum can disrupt the flow of fuel, cause complications in burners, and ultimately affect system efficiency and performance. Choosing a threshold like 15 inches of Hg reflects established industry standards for the safe operation of fuel oil systems.