Is this a pressure release valve?

I know nothing about sprinklers, except that our new (to us) house has them and I didn't turn them off last winter. There is water shooting out of this piece next to one of the controllers. The piece is capped off with some sort of filter, but when I turn the water on it shoots out of a 1/4" hole.

Here is an action photo:

http://www.writeorama.com/images/hosed/hosed.html

It looks like it is glued on. How do I take it off and replace it? Also, am I going to electrify myself?

Thank you very much.

That's an 'automatic' drain valve. It's supposed to close up, once the water pressure is applied. Buy a new one, and if that's all the damage you suffered for failing to winterize the system, then consider yourself lucky.

Thanks! Do I just crank on it to remove it?

It appears to be glued on. Do I just crank on it with the right wrench to remove it? Thanks!

There should be 1/2 inch male threads on the device.