PD Blower Replacement cross reference Chart
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The Power Equation You Get More!

The best measure of performance is power.

This is because most system units use a centrifugal pump and ones not a  P.D.  A Positive Displacement machine uses more energy and pulls harder the more the hose is filled with material; a P.D. vac pump attempts to maintain the same air volume and will draw higher amperage to maintain air flow as the system load increases. 

For example, with 50 ft. of 2" I.D. hose connected to the 15 Hp unit, the system will develop about 5" Hg. and draw about 9A (assuming 460V operation).  When the system begins to draw material, the vacuum increases and the amperage draw increases as the vacuum pump attempts to maintain the same air flow.  The system vacuum will continue to increase as the material load increases right up to its maximum vacuum potential (12" Hg), at which point the motor will draw 18A. The difference between 5" Hg. (9A) and 12" Hg. (18A) is the unit’s potential to do work.

In general, a P.D. powered system can be conservatively sized at 2.5 - 3.5 cfm/lb of material, whereas a centrifugal needs 5 - 7 cfm/lb of material, and it is not forgiving of plugging.  A centrifugal unit draws its maximum energy when NO material is in the system and plugs easily without operator training.

Finally, a P.D. vacuum producer is far more mechanically efficient: