How much pressure did steam locomotives work under?

Chris - A listener, David in Fincham, has informed us that mainline trains ran at 17 atmospheres, the Flying Scotsman at 15 atmospheres and older models around 10 atmospheres. Also, Mr. Wikipedia tells us that high pressure steam locomotives operated between 23 and even up to 100 atmospheres, that's 1500 psi, but they did need special design to do that.