INTRODUCTION
Pumps can be operated over 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. This 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 and 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:
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, that is the design speed of the pumping units. RPM must be considered, together with the
required head and desired throughput (GPM or BPH), to establish maximum efficiency in design. Optimum
standard military pipeline head capacities are contained in FM 5-482 (Military Petroleum Pipelines Systems),
and provided in Table 1. The maximum head capacity of a pump station is the total head against which it
will pump to provide maximum pipeline capacity. Maximum head capacities are only for use in emergency
operations and are never used in normal operations. Pump stations should not be operated at maximum
capacity except for emergencies. Operation under emergency conditions should not exceed 24 consecutive
hours.
PART C - PARALLEL AND SERIES INSTALLATION OF PUMPS
Electrical storage batteries are described in terms of series or parallel hook-up. In order to get 12 volts of
electricity, two 6-volt batteries may be connected in series. The same two 6-volt batteries connected in
parallel provide 6-volts of electricity, but the current is doubled. A hydraulic system is very similar to an
electrical system because the head capacity resembles voltage and the flow rate resembles the current.
5-2
QM 5096
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