What component prevents compass fluid from bursting out of the case during temperature changes?

• A. The case is sealed with a flexible metal diaphragm
• B. There is a vent that opens with pressure
• C. The fluid is non-compressible
• D. The case is made of glass

Answer: (A)

Expansion of the compass fluid with temperature changes must be accommodated to keep the pressure inside the case from increasing. The case is sealed with a flexible metal diaphragm that can flex as the liquid expands or contracts. This diaphragm provides an expansion chamber, allowing the fluid to increase in volume without building dangerous pressure or leaking. Because of this flexible seal, the compass remains closed and safe through temperature swings.

A vent that opens with pressure could relieve pressure, but it would not maintain a continuous, leak-free seal while still accommodating volume changes. The idea that the fluid is non-compressible doesn’t address expansion, and a glass case doesn’t provide the necessary mechanism to absorb liquid volume changes.