how can i clear an air lock from a farm irrigation system?

HAVE INSTALLED ANOTHER WATER TROUGH ON A FARM WHICH IS SUPPLIED FROM A BORE..PIPING TO THIS OUTLET WAS LINKED TO EXISTING PIPING PROVIDING WATER TO OTHER OUTLETS...NEW PIPING IS APPROX 150 METRESLONG...ARE UNABLE TO ESTABLISH A CONTINUOUS SUPPLY OF WATER TO THE NEW OUTLET...ALL OTHER OUTLETS ARE WORKING FINE...