Reddit reviews Orbit WaterMaster Underground 51240 1/2-Inch Plastic Auto Drain Valve
We found 1 Reddit comments about Orbit WaterMaster Underground 51240 1/2-Inch Plastic Auto Drain Valve. Here are the top ones, ranked by their Reddit score.
Easy to install1/2-inch male threadedOpening pressure: 3 to 5 psi (0, 2 to 0, 34 bars)Closing pressure: 5 psi (0, 34 bars) or greaterFor outdoor use with cold water Only
In most cases, you don't need to do anything other than shutting the water off. Most systems will have drains like these that will automatically open when the pressure drops.
I've never seen a system with a 'manual bleed' valve like you describe, but I'm certainly no expert. Every place I've lived around here has had a system with drains, but there unfortunately isn't a reliable way to tell if the person who installed the system actually put drains in.
Based on your pictures, my gut feeling is that you're probably okay, as your valves don't look too old (I've lived in a place that had the same valves), and you probably don't need to do anything else. However, if you want a professional opinion, you could take those pictures to a nearby Sprinkler World location and ask them. (They're open this time of year because they also sell Christmas lights.)