Hot Water posted:Big Jim posted:smd4 posted:you're adding cold water to the boiler and cooling it off, so the pressure goes down.Steve,
I am surprised that YOU, of all people, would say that! You are most definitely not putting cold water in. Much to the contrary, the water is very hot. The loss of pressure is that you are using boiler pressure to operate the injector.Nope! That has NOTHING to do with using the injector, since the boiler pressure through the injector goes right back into the boiler. The boiler pressure drops a bit because the injector supplies water that is NOT as hot as the large volume of water that is already in the boiler. No, the injector doesn't supply "cold water", but it DOES supply water that is "cooler" than the boiler water, and on smaller boilers, the pressure can drop significantly if the injector is left running too long.
Besides, what you might consider "very hot", say 180 degrees?, is no where near the boiler water temperature, anyway. On the other hand, a Worthington Feedwater System will pump "cold water" into the boiler if there is no exhaust steam to preheat the water to temps above 180 degrees.
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.
