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 After determining the pressure change, convert it to feet of water, the usual pressure
unit used on pump curves. This is sometimes called feet of head. They are the
same. Multiply the PSI times 2.3 to convert to feet of water. For example, our
example pump had a pressure change of 10 PSI. This is:
10 PSI x 2.3 = 23 feet of water
The final step is to use the manufacturer's pump curve to determine what flow rate
the pump will provide working at that pressure change. Using Figure 3-14 as an
example, the 23 feet of pressure change across the pump indicates a flow rate of
about 30 gallons per minute.
NOTE
While this method is reasonably accurate, it is not perfect. As
the pump impeller wears, flow rates will decline. If the pump
is moving glycols or oils, there may be a considerable deviation
from the published pump curve. If the flow rate is 50% higher
or lower than the design flow rate, consult the fluid manufacturer
for the correction factor.
FIGURE 3-14
A Typical Pump
Curve
The motors of wet rotor pumps never require lubrication. External motor pumps
should be checked at every inspection. If there is no way to determine lubricant
levels, a regular schedule for adding oil should be established, to avoid over-oiling
the motor.
INSPECTION
79
3.1 INSPECTION PROCEDURES
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