Spa Son

Okay - I've figured out it's called a dually but that's as far as I can seem to get

I need to replace a pump seal on what I can only describe as a double ended pump - there are wet ends on both side of the motor (I've nicknamed a pushme-pullyou pump)It's on a Cal Spa but I've never seen one before and want to find out more about them before I commit to the repair job. Anyone know what it's really called and where I can find out more - maybe even the pump seal it uses ?

I've always been told to fill a spa with cold water - not hot water from a water heater. I can't seem to find any source material as to why not.