Boiler pressure still messed up?
- Thread starter Xenithar
- Start date
This is extraordinarily helpful, Zec . Many thanks for posting it. I had always been puzzled about what a flashing yellow cut off meant and have lost speed trying to fix it it with the regulator.
I have started paying attention to the steam chest pressure and found it to be very useful for dialing in in a locomotive. With full cut off, the steam chest pressure begins to decrease as the speed increases; I am not quite sure the reason, but I suspect it has to do with the increased speed not allowing the steam time to fully expand leaving exhaust at a higher pressure. I would love a more accurate explanation if someone could provide it.
Once I see the steam chest pressure decrease, I start to dial back the cut off until it increases again to close to the boiler pressure. With further speed, the steam chest pressure decreases again and I repeat dialing back the cut off. This gets the engine up to speed efficiently and quickly.
I assume that in the prototype, there was no gauge that measured steam chest pressure and that this was all done by feel.
Great stuff to learn!
ZecMurphy
Community Assistant
Hi Frimbo
Essentually what is happening is that the regulator/steam lines can only provide steam up to a particular rate. As the cylinders operate faster, they consume more steam and eventually get above the rate it can be provided from the boiler. Reducing the cut-off reduces the amount of time the valves are open to let steam into the cylinders, which reduces the steam consumption. The expansion of the steam will still drive the cylinders at the higher speeds, so you don't need as much steam to keep the train moving.
Steam chest pressure gauges do exist, and appeared from I think the 1910s onwards. With, or without, the crew would still read the loco by feel, and sound, to get it 'right'. However, they are on a lot of locos today to help crews read the the loco better, as they tend to have a lot less running hours. Some locomotives had cut-off gauges or similar which worked in a similar way, but gave an indication to the driver if the cut-off was in the right place (I'm not 100% sure how these work, but IIRC it's still somewhat based off steam chest pressure).
Regards
Essentually what is happening is that the regulator/steam lines can only provide steam up to a particular rate. As the cylinders operate faster, they consume more steam and eventually get above the rate it can be provided from the boiler. Reducing the cut-off reduces the amount of time the valves are open to let steam into the cylinders, which reduces the steam consumption. The expansion of the steam will still drive the cylinders at the higher speeds, so you don't need as much steam to keep the train moving.
Steam chest pressure gauges do exist, and appeared from I think the 1910s onwards. With, or without, the crew would still read the loco by feel, and sound, to get it 'right'. However, they are on a lot of locos today to help crews read the the loco better, as they tend to have a lot less running hours. Some locomotives had cut-off gauges or similar which worked in a similar way, but gave an indication to the driver if the cut-off was in the right place (I'm not 100% sure how these work, but IIRC it's still somewhat based off steam chest pressure).
Regards