The pump won't work at all or badly until the air is flushed out.
Ditto for the piping.
You usually need about 1 to 1.5 m/sec velocity to "sweep" out air in pipes.
Very vague question so a general response.
Do you have a more specific issue / problem?
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.