Hot water pump and coolers

[nw-mailing-list at nwhs.org]

Veterans,

What is the purpose for a 'hot water pump' on a steam locomotive?  Pumping
from where to where?

Also, what is the purpose for a 'cooler' or 'after cooler'? I presume it's
to cool water (or steam), but why?

Thanks,
Dave Willis
N&W Steam lives on in Indiana.