One check valve is sufficient. The valve's primary purpose is to prevent water from a livestock tank being syphoned into well through a hose submerged in contaminated water.

Thanks Klem1, So that check valve should go in at the start of the run? I haven't dug it up yet, but I expect to see a T cumming out of the well then one line going to the house and one line going to the existing yard hydrant.

I presume you mean a backflow preventer? One is sufficient because it doesn't care what is downstream from it...you could have 20 yard hydrants ;-)

Just make sure you put it in an accessible valve box and don't simply bury the valve in the ground.

I live in an urban area and I'm required to have one valve for the water supply to the house and another to my yard irrigation system. And the water utility requires them to be tested each year.

A few things:

A check valve is just that - prevents water from moving backwards.

A backflow preventer is more sophisticated and usually includes vacuum breaks and multiple check valves in an integrated device. They are used to prevent potential contamination of a common water supply.

There are also less sophisticated vacuum breaks built into a lot of outdoor hydrants / hose bibs.

A good practice would be what Kudzu suggested, a backflow preventer in a box in the ground to prevent potential contamination of your well.

FYI: Lazypup passed away several years ago.

Our in-ground sprinkler system required a back-flow preventer where it connected to the water line, but only one was required. The sprinkler guys installed it in the box where the system connected to the main water line. It was in a warm climate, so protection from freezing or ability to purge the system of water was not an issue.

Bruce