Case of how air got into the piping

How does pumping away reduce air inside a hydronic system? For years, I couldn't understand it. Then I got it. Air doesn't get sucked in, it's already there. The pressures inside the system when a pump is on the return releases this pesky buggers and they do their best to interrupt heat to the radiators.

[@iansinclair521]

Good explanation, Ray

[@boilerroomdetective]

Thanks Ian

[@oilandfireguy1739]

Ive listened to lots of dan holohan and gil carlson (havent read the books)but you just explained why to pump away better than any one else ive heard! The point about the compression tank taking the extra pressure explains why its the point of no pressure change better than ive heard explained before!

[@boilerroomdetective]

Thank you very much I appreciate that

[@irishmike4914]

As we have talked about before,if you shake a bottle of water and open it.pssss