What piping arrangement or device prevents the complete loss of boiler water if a return line breaks?

The Hartford Loop is designed specifically to prevent the complete loss of boiler water in the event of a break in the return line. This piping arrangement consists of a horizontal pipe connecting the boiler to the return line, typically configured with an elevation drop between the boiler and the return system. In the event of a break in the return line, the Hartford Loop ensures that water remains in the system, utilizing the principle of maintaining a sufficient water level in the boiler, thus preventing the boiler from running dry, which could lead to serious damage.

In contrast, other options do not serve this specific purpose. A surge tank is typically used to accommodate fluctuations in water levels but does not prevent water loss in case of a return line failure. A drain valve is designed for the removal of water from the system, not for retention during failures. An expansion tank is used to absorb excess pressure caused by thermal expansion in the system but does not protect against the loss of boiler water through a broken return line. Therefore, the Hartford Loop is a crucial safety feature in steam systems, ensuring water retention under failure conditions.