what coolant flow do i need for liquid cooled spindle's

If a heat exchanger is being used, you should be fine with 45 liters per hour (L/h). A heat exchanger is a radiator that the water will flow through that typically has a fan to provide convection to transfer the heat off of the fins of the radiator. Our pumps have a flow rate of around 400-800 L/h. Additional Information: Here is the water cooling kit we have available for spindle cooling. https://buildyourcnc.com/item/pneumatic-hydraulic-spindle-inverter-cooling-water-pump-reservoir-fan-radiator-g14fittings-silicone-tubing