After pressure testing and prior to evacuation, all air and moisture must be removed to the extent possible, by emptying purge oxygen free nitrogen and, possibly, with the help of heated air. Significant amounts of water in the system cannot be solved in practice with the help of a vacuum pump, because it takes too much time. The principle of evacuation to reduce the pressure of any moisture left in the pipeline to saturation temperature below ambient temperature, turn off the vacuum pump and observe any increase in pressure, which indicates a leak or a large amount of moisture in the system that should be boiled away. Then vapor pressure can be lowered as much as possible. Pressure of saturated water vapor, expressed in units, all as absolute pressure, as shown in Table 11.1 (see also the units of measurement in Annex).
Vacuum pump must be connected to learn from all parts of the circuit. This may require two connections to get around the restriction, such as expansion valves and valves should be opened in the chain, requiring power supply of the solenoid valves and operation of theft screws on which they are installed.
Final vacuum-pressure shall be lower than the vapor pressure of water at the bottom of the system and, therefore, depends on the temperature of the system in its coldest point.
This process can be accelerated using triple evacuation procedure, which includes breaking vacuum oil-free nitrogen to help absorb moisture and again evacuation.
On small systems, such as factory packages, typical for a final pressure of 50 |im Hg (7 PA) must be achieved. Vacuum pumps of high quality that will endure refrigerant gas should be used. Evacuation of a large system can take several days. During this time, a check must be performed around pipes for cold patches, pointing to the boiling water and heat is used to get this away.....