Water flow measurement is critical to insure that the components of the resistance welder and especially the electrodes are receiving the proper amount of cooling water during operation.
Open Drain - The simplest method if you are using an open drain is to run the exit water line from each component on the welder into a bucket for one minute and measure the water in the bucket. the ideal amount for the electrodes is 1.5 gallons/minute.
Closed Loop/Cooling Tower – You cannot break the exit line and take a reading because you would be eliminating the head of water back to the cooling tower. In this circumstance you must use an in line flow meter on the exit side to register flow for each component.
Reference: RWMA Resistance Welding Manual 4th Edition