Agree with Dave. Balancing valve would not have an adjusting element, which is what that wing nut thingy on the top looks like. Pressure regulator is more likely, or possibly some kind of funky filtration element. Any pressure tap ports?
I am inclined to agree with "btrueblood".
I think it is a Filter or Strainer.
The "Wing Nut" on the top would be to remove and replace (or clean) the cartridge.
Definitely looks like regulator although inlet and outlet appear to be pvc pipe. So neither side under high pressure. May just be for crude pressure control.
Maybe a backflow preventer of some sort. Just another possibility