valves if you need to fetch a strong light source.

• The pressure will equalize and you will see a swirling motion in the pail as the flow of solar fluid into and out of the loop stabilizes.
• The solar fluid in the pail will go a milky white color because there are millions of tiny air bubbles passing through it.
• As the last of the air exits the system, the bubbles will get smaller and smaller. You need to get as many as possible out, no matter how tiny they are!
• When the pump has been running for a while, the milky color will fade.
• Eventually, the bubbles will stop.
• Keep the pump running for another five minutes.
• Slowly shut off the filler and drain valves, maintaining pressure of at least 10lbs/in².

When all the air is out of the system, both valves are closed and the pressure is in the right range, you can move on to the third step of pressurizing the system.

Bumping the bubbles

There are ways to help the air out of the system:

• Kink the drain hose a bit and let the pressure rise a little, then release quickly. This gives an extra push.
• Kink the drain hose a lot, quickly, and release it just as quickly. This makes the pipes shake, jolting trapped air bubbles.
• Turn off the charging pump from time to time, to allow the bubbles to settle out of the charging pail, then resume pumping.