To read rate of flow in GPM, drop down to the X axis and read the answer 850 GPM.
To determine the efficiency, drop down to the efficiency curve and read the percent efficiency in the
right-hand margin (70%).
The BHP is similarly read. Drop down to the BHP curve for gasoline and read the answer (35 BHP).
NOTE: BHP is expressed with a given specific gravity fuel. For design purposes, we use 0.8524 specific
gravity diesel fuel.
PART E - DETERMINATION OF PUMP SPEED
Individual pump stations must regulate pump speed to keep suction pressures at the next pump station
downstream above the minimum. The normal suction pressure at a pump station is 20 PSI for elevations
less than 5,000 feet and where temperatures are below 100 degrees Fahrenheit (20 PSI is equivalent to 64
feet of head of MOGAS). The minimum suction pressure at a pump station must be 5 PSI because of pump
entrance friction losses and the possibility of vapor lock in the pump. Five (5) PSI is equivalent to 16 feet of
head of MOGAS. To determine flow rate, efficiency, and BHP in pump station operations, the total pressure
produced on the discharge side of the pump station must be determined first.
EXAMPLE: There are three pumps on line connected in series and operating at 1800 RPM with a discharge
pressure of 480 PSI and a suction pressure of 20 PSI. They are pumping a product which has
a SP/GR 0.8254.
480 PSI minus 20 PSI = 460 PSI.
2.31x460
H
1,287
0.8254
In order to use the pump graph, divide 1,287 ft/hd by three because there are three pumps on line (429
ft/hd). Locate 429 feet of head on the graph, read to the right of the head curve (1,800 RPM). Read down to
600 GPM. At that flow rate, read up the graph until the line intersects the brake horsepower curve at 1,800
and read 68 BHP. This represents one pump and there are three on line. Multiplying by three gives you 204
BHP for the station. In the same manner, read up to the efficiency curve and read 74 percent. As shown,
the graphs can be used for pump stations as well as individual pumps.
800 GPM Main line Pump Graph. This pump graph (Figure 5-2) looks different but is constructed
and interpreted the same as the other pump graphs used. It shows total dynamic heads in PSI, feet of head,
and flow rate for water (1.0 sp/gr), DF-2 (0.8254 sp/gr), and MOGAS (0.7254 spgr) from 770 RPM to 2,100
RPM.
For example, at a flow rate of 500 GPM and 1,800 RPM pumping DF-2, the pressure and feet of head
can be determined. Locate 500 GPM and read up to the 1,800 RPM curve. Reading to the left gives 1,359
ft/hd at 500 PSI.
5-4
QM 5096
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