What happens when the relief valve discharges in a low temperature hot water system operating up to 250 °F?

When a relief valve discharges in a low-temperature hot water system operating up to 250 °F, the discharge immediately flashes to steam due to the sudden drop in pressure as the hot water escapes the system. Relief valves are designed to prevent excessive pressure buildup in the system by allowing fluid to exit when pressures exceed safe levels.

Given that the water in the system is heated to a high temperature, when it is released through the relief valve, it encounters the lower pressure of the atmosphere outside the system. This pressure drop causes a rapid change in the state of the water. Since the water is already at a high temperature, it does not require much of a reduction in pressure to transition from a liquid to a vapor phase, resulting in the immediate formation of steam.

This is a critical safety feature in hot water systems, as it helps to prevent potential hazards associated with overpressure, such as pipe failure or explosions. Understanding the behavior of water under varying pressures and temperatures is essential for ensuring safe and effective operation of steamfitting systems.