Plumbers Do It With Pressure Hoffman Differential Poster

Plumbers will enjoy this poster featuring the US Patent 1777333 by William K Simpson for The Hoffman Differential Loop along with the truism saying "Plumbers Do It With Pressure." The Hoffman Differential Loop, a device with no moving parts, keeps water in the boiler by making sure that under no circumstance could pressure in the boiler exceed 10 ounces higher than the return piping. It does this by bleeding pressure into the returns after 10 ounces was reached in the boiler. Thus, for example, if the boiler reached 11 ounces in it, then 1 ounce would be bled into the return pipes, since at no time could the return pipes be more than 10 ounces different than the boiler. What this means is that water would always be able to return to the boiler and steam would always flow since there was a differential pressure between the supply and return pipes. This device maintains an unvarying water line in the boiler independant of boiler pressure, which means that water in the boiler is never lowered to a point where the heat from the fire can exert a destructive influence on the boiler. Celebrate technology that is still applicable today in the home heating systems of old houses with this poster featuring a 20th century invention!