swing check valve

Steve_210

Hello Everyone. Please see photo of swing check valve. This is on the return line of a radiator of a 2- pipe air vented system. I have (3) buildings with 2 pipe air-vented systems that we are working on at the minute. They are all in the same neighborhood and i'm seeing a lot of these check valves. On all 3 jobs we have the pressure down to cutting out at about 14 ounces or slightly below 1lb. My question is: Does anybody think these check valves are original? I would think yes. As most of you here know, there are no steam traps on these radiators only hand valves with an air vent. The returns do not go to a wet return. They all join together like a ladder so you can have 6 radiators joined into a return riser before it drops into the wet return. What I'm trying to understand is the necessity for these check valves. I have a couple of areas in some of the buildings where I still have steam coming up the return before the supply and my thinking is, I should re-install some check valves. Looks like they were removed at some point, but i cant be sure. I then have to consider what type of check valve. Obviously, you want something that is going to open at low pressure or I will get water backing up in the returns. Hope this makes sense. Any Help greatly appreciated.