I'm not sure how hot the water is you're talking about, but if it's cooling jacket water below 200°F, then you can probably use circuit setters (also called circuit balancing valves) in each line going to the equipment. These valves are settable and have known characteristics along their range so that, for a given upstream pressure and pressure drop through the valve (measured with probes through integral ports on the valve), you know what the flow rate is. The handle has numbers on it so you know what the setting is.
It would be helpful to know the line sizes and some more information on the water, temperature, pressure, is the upstream pump a constant speed pump, etc.
Any hydronic pump rep can point you to a good source for these valves.