Vacuum is the term that designates the absence of matter in a space. Science admits that it is not yet possible to produce a perfect vacuum. Therefore, vacuum in an enclosed space - for example, inside a refrigeration system - means that that space has gases at a pressure well below atmospheric pressure.
Atmospheric pressure, at sea level, is 1.033kgf / cm 2 or 14.7lbf / inch 2 or 1 ATM or 760 mm Hg, at 0 0 C temperature. Thus, an enclosed space whose pressure is well below 1.033kgf / cm 2 or 760 mm Hg will be considered a vacuum. For refrigeration systems, where the vacuum pressure should normally be much lower than 1mmHg, a millitorr unit (mmTorr), equivalent to 0.001mmHg or 10 3 Torr, is adopted.
This value cannot be measured with standard pressure gauges. For pressures below 1 Torr, electronic vacuum meters are used, which indicate pressures below 50 mm torr.
