I need to check some three way bypass valves to see if the bypass is working or not. The original install was a bypass three way valve on many of the cooling coils. A retrofit a few years later was supposed to replace the valves (didn't happen) or block the bypass (maybe?) when they put VFDs on the CHW pumps. I think many of these bypass valves are still open because the CHW delta T is very low at low load conditions (as low as 3 degrees).

I've eyeballed the valves and don't see a blank-off plate installed. I was trying to measure pipe OD temperature at the coil and bypass ports but the bypass line is only about a foot long so I'm not seeing much of a temperature change with the valve in either position.

The best I've come up with is to put the valve in the closed position (full bypass) and wait to see if the chilled water line warms up. If it does, the bypass is blocked 9no CHW flow). If it doesn't, the bypass is still open. It may take a while (half hour to an hour?) for the outside of the pipe to warm up or make sure I didn't give up too soon. I didn't want to shut down cooling for that long. Have you got any other suggestions?