I'm a certified pool operator, but I've only worked on one pool and one spa for the last 13 years. Our spa at work has 3 pumps and 1 blower. 1 pump for the filter at 1HP, 2 pumps for the spa jets at 1.5 HP and one blower, which blows air into the jets.
I don't have any experience with residential spas. The ones I've seen only have one pump? One pump does the job of filtering and putting out the jets? I've seen spas with timers and controls on the spa itself. If there's only one pump, then how do the spa jets work? Do the controls increase the pump motor RPMs?