What thickness of foamglass is specified to cap the bonnet on a cold service valve insulation?

• A. 3 inches
• B. 2 inches
• C. 4 inches
• D. 1 inch

Answer: (A)

Insulating the bonnet on a cold service valve relies on delivering enough thermal resistance where the valve stem enters, so heat from the surroundings doesn’t transfer into the cold line and condensation is minimized. Foamglass is used because it’s rigid, has low thermal conductivity, and resists moisture, making it reliable for a bonnet-cap application. The specified thickness for this bonnet cap is three inches. This thickness provides the necessary resistance to keep the bonnet from warming up to ambient and reduces the risk of sweating and energy loss, while still fitting within typical space constraints. A thinner cap wouldn’t provide enough insulation, increasing condensation risk, while a thicker cap isn’t required and could add unnecessary cost or crowd the space.