Hot Tub Pump
All hot tubs will have one or more pumps used to produce the water high pressure needed for the jets to work.
Some systems use more that one pump - many have a main pump for the jet system and a separate pump for circulation. Very small circulation pumps don't always move enough water through the filters and as a consequence can lead to extra chemicals having to be added in order to maintain water quality. Where there is more than one main pump (and therefore more than one set of associated pipework) it is vital that the control system operates that system periodically to ensure that stagnant water does not build up in the plumbing in the event of that second system not being used.
If the pump system has a diverter it means that the pump is not capable of operating all of the jets simultaneously. Diverters cut the tub into zones where you have to select which zone is active.- this is fine if you are using the hot tub on your own but not so good if you have to "wait your turn" when bathing with company. Diverters can also inhibit the flow around the pipework and cause the pump to work harder.
Air blowers pump air into the hot tub - this can have the effect of lowering the water temperature if it does not pump warm air (some air systems use warm air from inside the cabinet).
All pumps need to be accessible in case maintenance or replacement is necessary and should be located near removable panels in the cabinet.