I'm work in a building that has a steam boiler with a one pipe pipe steam system. The store in the building has recently been renovated. Another contractor came in and installed a steam to water flat plate heat exchanger. The steam return line from the heat exchanger has an f&t trap and then ties into a wet return. There is banging coming from the return line of the heat exchanger. Some how i have gotten dragged into this. I told the contractor to remove the f&t trap and let it go straight into the wet return. He said the company requires an f&t trap on the return line of their heat exchanger. The company said the same thing when i called, even when i told them it drains into a wet return. Can someone please tell me why you need the f&t trap on the return of the heat exchanger if it ties into a wet return? Thank you.