Here's how I would do my own loop.
Shown is the air scoop with the air vent on top. On the right, next to it,is a flow valve. Open the valve by turning the triangular stem on top, circled, counterclockwise. In my case, I use zone valves instead of multiple circulators. There is a manual lever on them to open them. By introducing water to the boiler drain valve, I would now be pushing water up to the center zone valve in the direction shown. The other two valves would be closed off during this time.
Follow the arrows. The purge water is now traveling to the second floor radiators and coming back to my boiler. You can see part of a valve with a screwdriver slot. Not seen, behind the pipe is the hose bib, which is part of the valve. The slot would be turned to a vertical position to stop the flow of water back to the boiler and the other unseen slot will be open to allow water to exit the hose bib. Here, I would hook a hose and run it up to a point higher than my highest radiator. There are many other ways to do this, but this works well.
With the valves all in the correct position, let water slowly enter the boiler and up through the loop and eventually up and out of the hose on the second floor. Let it run until all air is purged.........5 minutes. Turn off the house water. Close the hose bib valve and purge the second zone the same way. When you're all done purging, return all valves and slots to their former position. Turn on the circulator and the rest of the air should be purged normally. If not, do it all over again.
In your case, your hose bib is above your circulator.
Here is another vent which is in my garage. There is no scoop associated with this one, but it's necessary nonetheless.;
Shown are isolation flanges. For the few bucks they cost, they will save you a bundle of time if you have to replace a circulator. If your system is down, install them. You can't have too many isolation points in a system.