can any one explain me working of a pressurization unit or make-up line in chilled water system?

Question

and wht is ment by primary and secondry pumps?

Answer 1

make up line or pressurisation units are used to keep the chilled water systems always "charged". usually such systems have a expansion tank at a height which keeps the system always under pressure and makes up for the losses.
primary pumps circulate the chilled water through the system and secondary pumps "charge" the chilled water system