Which type of steam trap operates on the principle that hot water under pressure flashes into steam when the pressure is reduced?

The correct answer is the impulse trap. This type of steam trap functions based on the principle of pressure reduction causing hot water to flash into steam. When the pressure of the water is lowered, the temperature at which water can exist in liquid form decreases, which allows some of the water to convert into steam. The impulse trap utilizes this principle by having a mechanism that responds to the changes in pressure and temperature, allowing it to efficiently discharge condensate while preventing steam loss.

Impulse traps are designed specifically to handle condensate in systems where fluctuating pressure and temperature conditions exist, making them well-suited for steam systems where such changes are common. Their operation is not reliant on buoyancy or thermal sensitivity, which distinguishes them from other types of steam traps.

In contrast, float traps rely on a buoyant float mechanism to control the discharge of condensate. Thermostatic traps function based on temperature changes, using a thermal element to open and close the trap as the temperature of the condensate varies. Inverted bucket traps operate on a principle of buoyancy and are often used to manage condensate in high-pressure steam systems. Each of these alternatives has unique mechanisms and applications that do not coincide with the flashing principle utilized by impulse traps.