I have a question I am hoping those of you with vast more knowledge then myself can help with. I was having a discussion with my boss about the proper location of an expansion tank in a glycol condenser water loop. We had a customer that had a glycol leak on a riser of their condensers water loop. The leak was on the 2nd floor of a 4 story building, drycoolers and pumps are on the roof. Due to the location of the leak, we had to drain the system down below the leak because there was no way to isolate the leak.
The top of the expansion tanks (two 100 gallon non-bladder tanks) are 3 feet below the highest point in the system. I was always taught/told that expansion tanks in this type of system (drycooler/pumps on the roof) needed to be at the highest point in the system and on the suction side of the pump. Especially if a non-bladder expansion tank. I asked the customer if they wanted me to raise the tanks up while we had the system down and drained. The mechanical prints even showed the tanks when installed were supposed to be above the highest point in the system. The customer asked me to throw them a price together real quick, so I did.

My boss turned around and told them not to worry about it said it does not matter where the tank is located. It could be in the basement, there just needs to be one on the system.

I did not think this was right, I said that the prints showed the tanks at the highest point in the system and should be there but could not come up with the reason why. My bosses reason that the expansion tanks did not need to be raised was because he has seen expansion tanks on hot water boiler loops in the basement so they do the job no matter where they are, just that there is one.

Looking for reasons why expansion tanks are placed in the system where they are.