What should be used to cap the bonnet on a cold service valve insulation with 3 in thick foamglass?

• A. Flat block foamglass 3 inch thick
• B. Wooden bonnet cap
• C. Flat block foamglass 2 inch thick
• D. Rubber cap

Answer: (A)

Maintaining a continuous insulating envelope around the bonnet is essential. The bonnet cap should be the same thickness and material as the surrounding insulation to prevent thermal bridging and condensation. Using a flat block foamglass exactly 3 inches thick matches the insulation there, preserving the cold surface and keeping heat and moisture from sneaking in.

A wooden bonnet cap would conduct cold and could absorb moisture, compromising insulation. A cap thinner than the surrounding insulation would leave an exposed area, reducing effectiveness. A rubber cap might not be compatible with foamglass or could deform and create gaps. So, the 3-inch thick flat block foamglass cap best maintains a continuous, effective insulation barrier.