Hey Sean,
In any case, a running spindle must not be disconnected any other way than by the RUN/STOP command of the VFD, and never by a switch, otherwise spindle or VFD could take harm.
If it has to be simple, I would connect the cooling station’s sensor outputs to VFD input terminals. The temp or flow sensor connected to an input terminal of the VFD can trigger immediate spindle STOP (if terminal is assigned to the corresponding function).
The VFD would then also be able to trigger stopping the running program on the CNC controller.
Image: KG5000+ Cooling station (back)
Left: Festo QS8 toolless hose connector, right: circular connector for temperature and flow rate alarm
Of course the system’s Safety relay circuit (e.g. Omron G9SE) or the CNC controller are also able to send RUN/STOP to the VFD if wired correctly.
To dimensionate the cooling system it’s the flow rate of the pump and the amount of coolant liquid (tank size) that matters. Expensive cooling stations have also bigger cooling windings and a bigger fan, here is one forum member that opened their device: Anyone using the Vevor CW3000 water chiller for their water cooled spindle?