Page 108 - An Introduction To Predictive Maintenance

98 An Introduction to Predictive Maintenance

pumped liquid. These passing frequencies can be calculated in the same manner as
the blade or vane-passing frequencies in centrifugal pumps (i.e., multiplying the
number of gears, lobes, vanes, or wobble plates times the actual running speed of the
shaft).

Running Speeds. All positive-displacement pumps have one or more rotating shafts
that provide power transmission from the primary driver. Narrowband windows should
be established to monitor the actual shaft speeds, which are in most cases essentially
constant. Upper and lower limits set at ±10 percent of the actual shaft speed are usually
sufficient.