Re: Boiler Pressure

Kevin,
The railroads based the locomotives boiler pressure from what kind of work the locomotives were going to be doing. The more pressure that the boiler is capable of operating with, the dryer the steam is and the more work it can do without using too much water and fuel. Size is not always a factor. Once they decided on what kind of pressure they thought they would need, then they worked on what kind of steel was going to have to be used, the thickness of it in certain places of the boiler, and then heating surfaces like grate area and tube length and thickness and the amount of tubes. Everything...
You can't design a 4-4-0 to have a boiler pressure of 300psi. It would be rediculous. It would slip so much you couldn't even run it. Then they say, "oh ok, then let's use smaller cylinders". Well that would be silly too because then you would have to use more steam and then it would still be slippery.
It just depends on what kind of work the locomotives are going to do. One way D&RGW and Baldwin compensated with the K-36's and working up 4% grades was first some very good boilers, that have such good heating surfaces, that even when working full out, can still lift the safety's. In other words, it's making more steam than it can even use. But that's with most "modern" steam power.
Kevin Bush