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A refrigeration vacuum pump is a device used to purge air conditioning and refrigeration (AC/R) systems of contaminants such as moisture and air. This purging action is achieved by inducing a deep vacuum in the system by continuously drawing small amounts of gas out over a protracted period. During this process, any water in the system is boiled off and the resultant vapor and any air is drawn out. Refrigeration vacuum pumps are typically rotary variants, many of which feature two stage operation. The vacuum values in question are expressed in microns with the average two stage vacuum pump capable of producing values of 50 microns or less.
Refrigeration and air conditioning systems often become contaminated with moisture and noncondensable gases such as air. The presence of either or both these elements in an AC/R system can cause serious problems such as internal icing and corrosion. If signs of these contaminants are detected or if the refrigerant charge has been drained for repairs, it will be necessary to purge the system. This involves connecting the refrigeration vacuum pump to the system and allowing it to run until such time as an acceptable vacuum has been drawn.
A refrigeration vacuum pump serves to eliminate air and moisture in two ways. The first is the physical drawing of air and water vapor from the system along with any remaining refrigerant gas charge. Moisture in liquid form can, unfortunately, not be drawn from the system in this way and needs to be converted to a gas or vapor to facilitate its removal. A refrigeration vacuum pump creates extremely low pressures in the system causing the water to boil at room temperature and be drawn out as vapor.
Refrigeration vacuum pumps are typically off-set rotary or scroll type pumps. Many deep vacuum pumps feature twin stages which are basically two identical pumps run in series. This type of pump can pull a vacuum of 250 microns with ease and may even produce pressures of 50 microns or less. To illustrate the depth of this type of vacuum, the micron pressure of air at sea level is approximately 760, 000 microns!
Refrigeration vacuum pumps are available in a number of capacity ratings ranging from approximately 1.2 to 10 cubic feet per minute (CFM). It is important to ensure that the vacuum pump used is appropriately rated for the particular size of AC/R system in question. Using a pump that is too small can cause unnecessary wear and possible damage. It is also essential to maintain correct oil levels in the refrigeration vacuum pump during purging operations.
The pipe length must be considered. As mentioned earlier, the vacuum sewer method utilizes the atmospheric pressure for the sewage disposal. The vacuum station is normally operating at a vacuum level of 60-65 kPa. The vacuum level in the interface unit at the discharge valve shall never be less than 25 kPa and the lift in the interface unit shall normally not be higher than 1.5 m. As a general rule, the loss of vacuum between the station and to any interface unit shall not be higher than 3.5 m.