Nice response and answer, Steve.
An additional point about injectors is, the water volume can be throttled back, so that the injector (regardless of type & size) is only "dribbling" water into the boiler. During such use of the injector when the engine is working lightly, with sufficient fire in the firebox, the boiler pressure does NOT DROP.
Now, concerning feedwater systems, first the Worthington "open type" ( type S and SA), there is NO "limiting feature" to prevent either the Fireman nor the Engineer (on those railroads where the Engineer had control of the Feedwater System) from operating the system with the THROTTLE CLOSED! Thus, the Worthington system will indeed pump cold water (cold enough that one can put your hand in the water without danger) into the boiler. Also, with the Worthing and Elesco Feedwater Systems, boiler pressure is used to operate the cold water turbine pump plus the high pressure feed pump (thus those types of feedwater systems actually use more boiler supplied steam than, say a Nathan non-lifting injector), while ONLY the exhaust steam is used to preheat the feed water. In other words, if there is no exhaust steam, then there is NO preheating of the feed water, and it is then COLD WATER. You want to see the boiler pressure drop VERY RAPIDLY, then operated the Worthington Type S or SA system with the throttle closed!!!!!
As additional information, the Elesco Exhaust Steam Injector type of feedwater system has a change-over valve internally, thus that feedwater system can be used when the throttle is open or closed, and the feed water is STILL pre-heated, by either exhaust steam or boiler "live" steam.
