Well, I understand how the injectors work, and, as Bernhard points out, the injector does impart heat to the water. But that raises the question of why railroads would then bother with a feedwater heater system at all.
From reading further in the Locomotive Cyclopedia, it seems that the answer is in fuel savings - the otherwise waste heat from the exhaust steam used in a fwh is sufficient, on average, to raise the water temperature by 160 deg F. - with feedwater at 60 deg., that's 220 deg. F. as the water enters the boiler, all of that gain at almost no extra cost in fuel. (Some boiler steam is used to run the cold water pump.)
In an injector, the water temperature is raised only to 180 deg. F., but the "live" steam required had to be produced by the boiler for this purpose: in other words, fuel had to be burned to produce the steam solely for the operation of the injector.
Either way, whether at 180 deg. or 220 deg., the fire still has to raise the water temperature to about 600-650 deg. F., the normal operating temperature of steam in the boiler at normal operating pressures.
Because the water from an injector is impelled by live steam at boiler pressure, it's able to open the boiler check valve, admitting the water. In a fwh, using waste steam at lower pressure, the check valve is held open by pressure supplied by the cold water pump.
I appreciate all the assistance and information added by others, and welcome more - my information is only from books, so first-hand knowledge is particularly useful.
Wayne
From reading further in the Locomotive Cyclopedia, it seems that the answer is in fuel savings - the otherwise waste heat from the exhaust steam used in a fwh is sufficient, on average, to raise the water temperature by 160 deg F. - with feedwater at 60 deg., that's 220 deg. F. as the water enters the boiler, all of that gain at almost no extra cost in fuel. (Some boiler steam is used to run the cold water pump.)
In an injector, the water temperature is raised only to 180 deg. F., but the "live" steam required had to be produced by the boiler for this purpose: in other words, fuel had to be burned to produce the steam solely for the operation of the injector.
Either way, whether at 180 deg. or 220 deg., the fire still has to raise the water temperature to about 600-650 deg. F., the normal operating temperature of steam in the boiler at normal operating pressures.
Because the water from an injector is impelled by live steam at boiler pressure, it's able to open the boiler check valve, admitting the water. In a fwh, using waste steam at lower pressure, the check valve is held open by pressure supplied by the cold water pump.
I appreciate all the assistance and information added by others, and welcome more - my information is only from books, so first-hand knowledge is particularly useful.
Wayne