Figure 3-11 Calibrated Gauges With the Pump Off and On

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If the two gauges read the same when the pump is off (Figure 3-11), the differential
pressure is simply the outlet pressure minus the inlet pressure. For example, if both
gauges read 30 PSI with the pump off, and when the pump is on the outlet gauge
reads 35 and the inlet gauge reads 25, the differential pressure is:
35 PSI - 25 PSI = 10 PSI
FIGURE 3-11
Calibrated Gauges
With the Pump Off
and On
However, if the gauges read differently when the system is off (Figure 3-12) and
cannot be adjusted to agree, you have to add up both pressure changes. For
example, at rest, the inlet gauge reads 28 and the outlet gauge reads 30. When the
pump is on, the inlet gauge goes to 23, and the outlet gauge goes to 35. The total
of the pressure changes is:
For the inlet gauge: 28 PSI - 23 PSI = 5 PSI
For the outlet gauge: 35 PSI - 30 PSI = 5 PSI
The total pressure change is: 5 PSI + 5 PSI = 10 PSI
INSPECTION
3.1 INSPECTION PROCEDURES
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