What type of steam trap relies on the variable density of condensate?

The correct answer is that a steam trap that relies on the variable density of condensate is a thermal steam trap. Thermal steam traps operate based on the principle that steam and condensate have different thermal properties, specifically different densities and heat content. As steam condenses into water, the density changes, and this difference can drive the mechanism of the trap, allowing condensate to be expelled while retaining steam.

Orifice steam traps, on the other hand, function by creating a fixed opening through which condensate is expelled. Their operation is not dependent on density changes, but rather on flow rates through the orifice. Pneumatic traps utilize air pressure to operate and do not rely on the density characteristics of condensate. Mechanical traps typically use moving parts, such as float mechanisms, and their operation is based on physical movement rather than variable density.

By understanding that thermal traps leverage the changes in density of steam and condensate, one can see why this answer accurately fits the question. The unique relationship between the two states is crucial for the thermal steam trap's ability to function effectively in expelling unwanted condensate while retaining steam.