Big Jim posted:Yep, it has everything to do with the injector!
The boiler pressure through the injector does not go back into the boiler. The boiler pressure turns the water into velocity, via the injector, and that is what forces the water past the check valve into the boiler. Now, almost all of the HEAT from the steam used to work the injector is retained in the feedwater and that is what DOES go back into the boiler!So let's go back to your incorrect temperature scenario. Remember that WATER is going into the boiler. Water from the injector, getting it's heat from the boiler water at pressure (go look at the temperature/pressure charts to see just how hot the steam is starting out) and water from the feedwater heater, getting it's heat from the exhaust steam, are both going to be very (for all intents and purposes) close in temperature. The reason being that the feedwater heater being an open (to the atmosphere) system has water that can't be very much more than 212° F.
So, your temperature scenario is moot. So why would running the injector lower boiler pressure and running the FWH not? The water from both is about the same temperature. Well, the reason is the way each system works. The FWH system uses a small amount of live steam to operate its pumps compared to the large amount of live steam that the injector uses to force water into the boiler. And, that large amount of steam used to operate the injector is exactly what sucks the pressure from the boiler.
Now, as for your Worthington FWH pumping COLD ( at ambient temperature) water into the boiler. You must have forgot the conversation that we had about this a number of years ago and was substantiated by others. Worthington designed their feedwater heater to limit the amount of actual COLD water that could be pumped into the boiler. Another thing about FWH's, how much they can pre-heat the water is directly related to how hard the locomotive is being worked.
Now, exactly how many steam locomotives have you fired, Big Jim? I'm guessing the answer to that is none, 'cause pretty much everything you wrote above is incorrect, or confused, or mistaken.
I have never operated an engine with a feedwater heater, so unlike you, I won't presume to know precisely how they function beyond the basics. Hot Water can address those issues.
I have, however, fired two engines with Sellers injectors, one for the last seven years (and one stationary boiler, with a Penberthy), so I think I can speak from a bit of experience here. For what it's worth, when I say "cold water" being injected, I'm referring to "relative" temperature. This is something I don't have to explain to steam guys, so my bad for not clarifying to a lay person. While the water being injected into the boiler isn't "cold," it sure as heck is a lot cooler than the 380 degrees that the water in the boiler is at 190 PSI, probably by 200 degrees cooler, despite your incorrect statements above. So yeah, relatively speaking, it's "cold."
The steam it takes to run the injector is minimal, so no, the boiler pressure doesn't go down because you use steam to run the injector--it goes down because you're cooling the boiler. It's simple thermodynamics--maybe something you don't need to worry about when running a diseasle, hmm?
