Water and other liquids circuit pressure tested for safety and leaks, using water at a pressure of 1.5 times the working pressure, or as needed. The ability to shoot when filling in for testing to make sure that the paths can be filled without airlocks. Air vents at high points of the circuit can be automatic or manual.
While the pipe is full, the pumps should be running, if possible, remove any dirt before draining down and purification filters. If a lot of dirt found, the pipeline should be filled again and reflushed. In any case, the pump should be started as soon as possible and filters are clean. Fluid if, in addition to water, not put until this crimp and washing was carried out...