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Technical Section Phone: 516-328-3970 www.technocnc.com  15 Router industry. The differences in a cost-to-performance ratio  from  one  system  to  another  are  best  described  by comparing the pros and cons of each system. For each system, a 10HP example will be used in relation to "Hg at scfm, decibel levels, approximate cost, typical applications and maintenance requirements. In comparison to the other vacuum systems, a 10HP regenerative blower is the lowest in cost, generally retailing for around $5,000. Regenerative vacuum blowers, consist of an electric motor coupled via belt or direct drive to the vacuum  pump  impeller.  The  motor  rotates  the  impeller, drawing air in the inlet and discharging the air through the exhaust, creating vacuum. Because the inexact dimensional tolerances from the impeller to the housing, air is allowed to escape, resulting in lower vacuum pressure. This is known as  slippage.  Regenerative  vacuum  blowers  typically generate low vacuum pressure, but generate greater volume of air as described in the earlier example of 11"Hg at 105 scfm. The noise consideration is a very real concern for these products. A regenerative vacuum blower runs in a decibel range of 85 to 95. This type of vacuum is ideal for holding  less  dense  materials  such  as  foam  and  other porous  materials.  The  required  maintenance  is  minimal with regenerative blowers, usually limited to replacing air filters. Rotary vane vacuum pumps also consist of an electric motor coupled via belt or direct drive to the vacuum pump impeller  made  up  of  self-lubricating  carbon  vanes.  The vanes rotate in the pump housing drawing air in the inlet and discharging the air through the exhaust, creating vacuum. Because of the close tolerances generated by the carbon vanes, greater vacuum pressure results. Up to 25"Hg at 173 scfm can be  achieved  for  an $8,300 10HP unit. The increased    vacuum results in superior hold- down capability, and is ideal for wood, plastic, and  other  nonporous sheet-like materials. In addition,  these  shop friendly pumps run quieter with a decibel range of 80 to 85. The  downside  to  using  these  pumps  is  that  the  carbon vanes  need  to  be  replaced  after  6000  to  8000  hours depending  on  conditions.  Increased  heat  in  the  pump reduces vane life; dirty and/or blocked air filters and relief valves will cause the vacuum pump to heat and decrease vane life. The electric motor for a positive displacement rotary blower is also coupled via belt or direct drive, but instead of carbon vanes it connects to two rotors that rotate in the opposite direction. When the rotors pass the blower inlet, it traps  a  quantity  of  air  through  the  blower  housing  and discharges this compressed air out the exhaust. Because the pump compresses the   air,   when   it   is exhausted  it  is  very loud due to the release of    this    pressure. Typical decibel ranges for a $8,500 10 HP unit run  from  95  to  100. Positive displacement rotary blowers should be enclosed providing some sound protection.  A max vacuum of 15"Hg @ 250 scfm makes these units ideal for wood, plastic, and other nonporous sheet-like  materials.  Regular  maintenance  such  as  oil changes  are  required  between  5000-6000  hours  of operation. Proper disposal of these oils are required. Lastly,  rotary  screw  vacuum  pumps,  which  are  the most costly pump at about $15,000 for a 10 HP unit, are ideal  for  wood,  plastic,  and  other  nonporous  sheet-like materials. They have their electric motor coupled via belt or direct drive to counter-rotating twin screws. These pumps are  the  most  complex  of  all,  but  also  yield  the  greatest vacuum at 29"Hg at 150 scfm. They require cooling systems with complex electrical system controls to operate the unit. Grid pattern offers maximum flexibility and provides easy customization of table surface. Regenerative Vacuum Blower Rotary Vane Vacuum Pump