Regenair® - Gast Manufacturing, Inc.

ReferenceREGENAIR ® Regenerative BlowersTechnical Information and DefinitionsDefinitions:CFM – cubic feet of air per minuted – density in pounds per cubic footSP – static pressure inches of water1 – known conditionsHP – horsepower2 – desired conditionsRPM – speed in revolutions per minuteStandard Air-air at 68 °F (absolute temperature 528°) and 29.92 inHg. (barometric pressure at sea level). The density of such air is0.075 lbs/cu ft. and the specific volume is 13.29 cu ft./lb The specific gravity is 1.0.H 2O CFM vs SCFMThe difference between “Cubic Feet Per Minute” and “Standard Cubic Feet Per Minute” is simply one of air density. The word“Standard”, in this unit of measure, refers to the air being at standard temperature and pressure. In this case it will have standardair density. Regenair blowers performance is stated in terms of CFM, the volume of air they move.Fan LawsThe following fan laws apply for the range of air performance where induction motor-driven blowers operate, that is, under 100inches of water static pressure or vacuum (where it may be assumed that air is incompressible). The fan laws may also be used ifthe pressure of both fan conditions is over 100 inches of water but the pressure change is less than 30%.1. Effect Of A Speed ChangeCFM is proportional to Speed CFM 2= CFM 1X (RPM 2/RPM 1)(The volume changes in direct ratio to the speed)SP is proporational to Speed 2 SP 2= SP 1X (RPM 2/RPM 1) 2(The pressure changes as the square of the speed ratio)HP is proportional to Speed 3 HP 2= HP 1X (RPM 2/RPM 1) 3(The horsepower changes as the cube of the speed ratio) (Also known as the 1-2-3 rule of blowers)2. Altitude And Temperature Change The Density Of AirCFM is constant CFM 2= CFM 1SP is proportional to density SP 2= SP 1(d 2/d 1)HP is proportional to density HP 2= HP 1(d 2/d 1)Volume Changes In Direct Ratio To SpeedFor example, a blower is operating at 3500 RPM and delivering 800 cfm. If the speed is reduced to 3000 RPM, what is the newvolume?Let:V 1– original volumeV 2– new volumeRPM 1– orginal speedRPM 2– new speedV 2= V 1X (RPM 2/RPM 1) 1V 2= 800 X (3000/3500) 1 = 800 X .857 = 686 CFMPressure Changes As The Square Of The Speed RatioFor example, a blower is operating at a speed of 3500 RPM and delivering air at 3 psi. If the speed is reduced to 3000 RPM, whatis the new pressure?Let:P 1– orginal pressure (3 psi)P 2–new pressureRPM 1– original speedRPM 2– new speedP 2= P 1X (RPM 2/RPM 1) 2P 2= 3 X (3000/3500) 2 = 3 X .735 = 2.21 psig = 83 inchesof water pressure70 Gast Regenair® Regenerative Blowers www.gastmfg.com