Steam Boilers–The Hartford Loop: Insuring Safety
In the dawn of the Age of Steam, boilers used to blow up with terrible frequency. There was none of that awful government interference with people’s right to be killed by unsafe products, and by goodness, killed they were. Coal fires weren’t easy to control, and systems were allowed to carry high pressures without a good way to relieve that pressure. Safety devices, especially ones to keep the boiler from “dry firing” didn’t yet exist. Dry firing occurs when there is a leak in the system below the water line. Water leaves the boiler and allows the fire to overheat the iron of the boiler shell. If more water is added to the vessel, the water immediately flashes to steam and if there is no way to let the pressure out, a bomb ensues.
Insurance companies began to insist on safer heating equipment, and among other improvements, a simple piping configuration which trapped the water in the boiler, keeping it isolated from any leaks below its water line, became accepted practice. It was called the Hartford Loop after the city central to the insurance industry.
A proper Hartford Loop is taken off the equalizing line of the boiler piping with its center 2″ below the normal water line. The shortest possible nipple and an immediate elbow turn the loop down to meet the wet return, forming a water seal. The connecting nipple must be short since this is the place where steam in the equalizer and condensate from the returns meet and water hammer will occur if there is room for the steam/ water slug to gain momentum. Water hammer from the Hartford loop will typically happen in mid-cycle. If you hear banging in your steam piping, you may well have an improperly piped Hartford loop.