Can Somebody Explain this Plumbing?

[af1]

Please see attached image.

This is in the crawl space, on the hot water line.

There is some kind of valve at the end of the pipe shown.

When I turn off the main supply water, then water comes out of this pipe (ie seems to open when water pressure is low).

Water will continue to come out until I have drained the hot water heater.

So - what is the valve called at the end of the pipe, and what is the purpose?

 

[havasu]

I can't really tell from the pic being washed out, but I'm wondering if it is used to drain the water lines for winterization?

 

[plumbtired]

That is what it is used for. Most of the time you see theses on repo houses. They go in install all for Winterization.

 

[af1]

What is the name of a valve that is closed for high pressure, and open for low pressure?

Does anybody foresee a problem with replacing the valve at the end with a sillcock?

 

[leatherlung]

It's hard to tell in the pic but I don't see why you couldn't put a sillcock on there.