Technical SectionPhone: 516-328-3970www.technocnc.com15but these few are the most commonly used units in the CNC 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 dimensionaltolerances from the impeller to the housing, air is allowed to escape, resulting in lower vacuum pressure. This is known asslippage. Regenerative vacuum blowers typically generate low vacuum pressure, but generate greater volume of air as described in the earlier example of 11Hg 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 fi lters.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 vacuumpressure results. Up to 25Hg at 173 scfm can be achieved for an $8,300 10HP unit. The increased vacuumresults 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 fi lters 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 thepump 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 r o t a r y b l o w e r s should be enclosed providing some sound protection. A max vacuum of 15Hg @ 250 scfm makes theseunits 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 29Hg at 150 scfm. They require cooling systems with complex electrical system controls to operate the unit. Grid pattern offers maximum fl exibility and provides easy customization of table surface.Regenerative Vacuum BlowerRotary Vane Vacuum Pump