Chilled water system and air locks

[Goober]

Can anyone clearly explain why an airlock in any given piece of pipe in any circulating water system, be it on a chilled circuit, hot water circuit etc can stop the flow of water? the air lock is in the pipe and not anywhere near the pump(S).

I have heard of this over the years but never really found out why and how? Even talking to one of my crusty old experienced plumber colleagues, who knows everything, he couldn't tell me.

[Brian_UK]

Assuming that there is more than one pipe branch....

Think of the air lock as a form of closed valve, it can reduce the flow of water in that branch as the water can divert somewhere else. Also, air being compressible it can form effectively a solid plug providing the water pressure /flow is not too high.

If you have 50mm pipe that has air trapped in it, with no escape, such that the air is taking up 40mm of pipe then with only 10mm left for the water the flow must be reduced.

[Goober]

[QUOTE=Brian_UK;271724]Assuming that there is more than one pipe branch....

Yes, but could it happen with a single circuit system?

Think of the air lock as a form of closed valve, it can reduce the flow of water in that branch as the water can divert somewhere else. Also, air being compressible it can form effectively a solid plug providing the water pressure /flow is not too high.

But how?...yes I understand the air being compressable, but surely it will eventually push against the water on the other side and eventually move the air lock along the pipe..that is providing we don't have the situation as you have described below and which I have discussed with said crusty plumber.

If you have 50mm pipe that has air trapped in it, with no escape, such that the air is taking up 40mm of pipe then with only 10mm left for the water the flow must be reduced.

Now this i understand...I suppose in the real world this is what actually happens and one never gets a 100% air lock taking up the full 50mm of the pipe. But, In the case of having the 50mm pipe full of air only surley the air lock would be moved along the pipe, eventually?