The heat exchanger cooling fan used on the Physical electronics 16-025 and 16-050 heat exchangers which are used to cool the x-ray sources on an XPS system can run slowly as the fan motor ages once the bearing lubricant begins to dry up. The result of a slow fan is that the anode will run warmer than normal and possibly melt. At a minimum reduced cooling will shorten the anode lifetime. The 16-020 heat exchanger has a fan that is attached to the pump motor, so it will not have this problem unless the pump motor fails.
The symptom for a slow heat exchanger fan is that with the source at full power after 20 minutes of operation the water lines to the x-ray source will be very warm or even hot rather than slightly warm.
To test the fan you can feel how much air is coming out the back side of the radiator when the 16-025 or 16-050 heat exchanger is on. The radiator will slow down the airflow, but it should still be a reasonable amount of air that escapes out the back side of the radiator. If the fan looks like it is spinning slowly and there is minimal airflow then the fan should be replaced.
If you want to test the actual RPMs of the fan you can use a non-contact laser tachometer (available for as little as $15.00). Or you can use an audio method as shown in this video on YouTube that uses Audacity:
The fan motor should spin at 1650 RPMs.
If you determine that the fan should be replaced (or if you want to as a preventive measure if your heat exchanger is 20 years old), here is the model number information –
Manufacturer – Orion
Fan, AC, 230V, 254 X 89mm, Round, 547CFM, 35W, 55dBA, 1650RPM
Manufacturer part number: OA254AP-22-1TB
Allied Stock # 70103674
It is held in place with some radiator mounting rods that are available at most auto parts stores. Look for Hayden Nylon mounting rods with vibration pads.
In addition to the cooling fan, if the pressure indicator on your 16-050 heat exchanger bounces during operation you should consider replacing the water pump as well. RBD Instruments provides the water pumps. The 16-020 and most 16-025 heat exchangers do not have a pressure gauge.
And of course, make sure that the radiator is free from dust as being covered with dust will also reduce the cooling efficiency of the 16-020, 16-025 or 16-050 heat exchangers. Refer to the RBD TechSpot post Heat Exchanger Preventive Maintenance for more information on dust and the radiator.
Heat exchanger preventive maintenance will prolong the anode lifetime on your 10-610 mono chromator anode and prevent a costly and time consuming anode meltdown.