Which type of heat cutoff device operates based on fluid pressure?

The correct choice relates to a type of heat cutoff device that utilizes fluid pressure as its operational principle. This device operates by responding to changes in pressure within a fluid system; when the temperature exceeds a certain limit, the pressure change triggers a mechanism that interrupts the electrical circuit or shuts down the system.

In contrast, a bimetal type device relies on the expansion and contraction of two different metals that are bonded together. This creates a mechanical response when temperature changes but does not utilize fluid pressure for its operation.

The melting type cutoff operates based on the melting of a material at a certain temperature, which activates the mechanism, but again, it does not involve fluid pressure as a variable.

Finally, a motion switch type device relies on detecting movement or the absence of movement, rather than responding to temperature or pressure conditions.

Therefore, the key distinction with the fluid pressure device is its unique reliance on pressure changes in fluids, which allows it to serve effectively in applications where thermal regulation is needed based on the behavior of liquids within the system.