a flow - regulating valve is located in the outlet of the housing of a centrifugal pump instead of in downstream piping , to regulate the flow from the pump without the usual acoustic disturbance caused by flow . the arrangement is especially adapted for hydro - therapeutic installations , such as a spa , hot tub , whirlpool bath or the like . the valve is operated by a control conveniently accessible to the occupant of the hydro - therapeutic installation . the control can be in the form of a knob connected to the valve by flexible cable or the like or in the form of a single push - button which controls both the electric motor for the pump and an electric motor which operates the valve .