Factors behind heritage railway steam engine use?

[alexl92]

I'm interested to know what factors come into play when a heritage railway decides which steam loco(s) to use each day.

I'm aware that on some railways, there are minimum requirements for power - such as on the NYMR where I believe they need a minimum of a BR power class 4 to haul 7 coaches up to Grosmont from Pickering. I'm also aware that in some cases, having the various bits of kit for mainline running are a necessity.

I'm interested to know the other factors that come into play. For example, if a railway was running a one train service for 5 consecutive days over half term, many would choose to run the same loco all week. Are there any factors that would define that or is it simply a decision of convenience?

What else comes into play when making these scheduling decisions?

Thanks!

 

[Cowley]

I remember from volunteering at the Mid Hants that the same loco would be used on the one train operating timetable a few days in a row because it was better to keep the loco warm as frequent cooling and heating up would put undue stresses on the boiler.
The loco would eventually be due for a boiler washout and would be allowed to cool down for this and any other repairs undertaken before it went back into service after being lit and warmed up (slowly) for it’s next stint.

 

[JonathanP]

On longer heritage railways the limiting factor on engine size isn't so much power, since even small locomotives can haul a fairly heavy train at 25 mph, but water capacity. The amount of miles a small tank engine can pull a heavy train with frequent stops but no time to fill up with water is quite low.