mystery check valve

[CHW]

Hello everyone. First posting and it's a mystery. Just disconnected all water lines at the hot water tank to drain and winterize water system. Have done this many times before. However, this time a small 3/4" long x 1/2" dia. bullet shaped spring check valve stem with a small "0" ring on one end showed up on the bilge floor without my noticing where it came from. Hot water tank drained quicker than ever so I am thinking that it must have come from the cold water supply connection. Supply line attaches to a 90 degree push in coupler mounted directly to the tank. Anyone ever have this happen and figure out where this stem inserts and in what direction?

 

[rondds]

My HWH has a plastic 3" nipple (1/1" diameter) with an inline check valve. I took it off several times and never lost any pieces of it. I'm sure you can find a replacement one - just not sure where.

 

[Daddubo]

My $.02 it might be a backflow preventer so the lines don't drain back to the tank.:smt017

 

[CHW]

I figured it out. Sea Ray sent me a schematic of the HW tank plumbing. A check valve was specified at the cold water fill and the cold water feed at the blender. After removing the 1/2" x 15mm fittings which had just looked like reducers I found that they had built in check valves and that a faulty "O" ring had allowed the mystery stem to blow back out. Easy fix with a replacement "O" ring. Also, if needed Seatech has this part. They call it a male stem check valve. Thanks to all who helped.