INTRODUCTION
Pumps can be operated at a wide range of speeds in order to compensate
for variations in the pumped product's specific gravity, temperature, and
the pipeline topology. The speed at which the pump is operated also
determines the efficiency and therefore the cost of operation. To
effectively direct a pumping operation you must be able to balance all
the operating parameters of the pumps which is accomplished by the use of
pump graphs.
PART A - FEET OF HEAD AND POUNDS PER SQUARE INCH
A pump graph is constructed to show feet of head, flow rate in gallons
per minute (GPM), and barrels per hour. Pumps are equipped with gauges
that register the suction and discharge pressure in pounds per square
inch (PSI). Therefore the operator must be able to convert PSI to feet
of head to determine the flow rate and efficiency of the pump.
2. 31xPSI
H
The equation for converting PSI to feet of head is
.
SPGR
2.31 is a constant based on a column of water at 60 degrees Fahrenheit, 2.31 feet high and measuring 1
inch by 1 inch. 2.31 feet of head of water at 60 degrees Fahrenheit equals 1 PSI. One foot of head is equal
to 0.433 PSI (1 divided by 2.31). By using the specific gravity of different fuels in the equation the operator
can determine the difference in PSI.
EXAMPLE: The fuel being pumped (DF) has a specific gravity of 0.8254.
The pressure at which it is being pumped is 325 PSI. Using the
following equation, it is calculated that the feet of head is 909:
2.31x325
H
.
0.8254
The operator knows the pump can overcome 909 feet of head.
HxSPGR
The equation for changing feet of head to pressure is P
.
2.31
EXAMPLE: A pump operator must overcome 909 feet of head while pumping DF
with a specific gravity of 0.8254 and needs to know the pressure which
must be maintained. Using the equation:
P = pump
H = Head
2.31 = constant
SPUR = specific gravity
909 x.8254
P
325 PSI .
2.31
PART B - EFFECT OF PUMP STATION OPERATION ON HEAD CAPACITY
AND FLOW RATE
The normal head capacity of a pump station is the total head against
which it will pump at the most efficient operating point for example, the
design speed of the pumping units. Revolutions per minute (RPM) must be
12-98
QM 5099
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