outward by centrifugal force into the volute of the pump casing. The
volute catches the discharge and converts peripheral velocity into head
pressure while conducting the liquid at a reduced flow rate to the
discharge nozzle of the pump casing. Different pumps are used on
aluminum and steel pipeline systems.
6-inch, Single-Stage Pump - The 6-inch, single-stage pump is a self-
priming, centrifugal pump equipped with a mechanical shaft seal.
Suction and discharge connections are grooved pipe. Maximum safe
working pressure is 207 PSI or 660 feet of head for fuel with a SG of
0.725.
6-inch, Two-Stage Pump - The 6-inch, two-stage pump is a multi-stage
pump fitted for external connection to operate either in series or in
parallel. Maximum safe working pressure is 700 PSI or 2,390 feet of
head for a fuel with a SG of 0.725.
800 GPM Mainline Pump - The 800 GPM mainline pump is a new pump used
for operation in an aluminum pipeline system. It is a skid-mounted,
three-stage centrifugal pump.
PART E - PIPELINE SCRAPER OPERATIONS
Scrapers are devices inserted into the pipeline to remove internal scale,
rust, or other foreign material. In the petroleum industry, scrapers are
often called "pigs" or "go-devils." Two types of scrapers are used:
Steel Brush Scraper - The steel brush scraper is constructed of a
tubular shaft on which are mounted two sets of four spring-loaded
steel brushes and two synthetic rubber cups. The spring-loaded steel
brushes clean the walls of the pipe. The front and rear brush groups
are staggered to cover the entire pipe surface. The tubular shaft of
the scraper is open at the rear, which permits a fraction of the
stream to flow into the scraper and escape through small ports near
the front end, thereby agitating and propelling the loosened scale
forward. This prevents the scale from accumulating ahead of the
scraper, causing the line to become clogged. This type of scraper
comes in 6-, 8-, 10-, and 14-inch sizes. The 10- and 14-inch scrapers
have three synthetic rubber cups.
Poly Pig Scraper Device - The poly pig scraper device is constructed
of foam-type material and wrapped with abrasives to clean the
pipeline. They are able to make 90-degree turns in the pipeline and
are inexpensive, though they do not clean as thoroughly as steel brush
scrapers nor are they as durable.
Military pump station manifolds have two scraper stations; one for
launching and another for receiving. Before launching a scraper, lines
should be free from sharp bends and valves that do not open the full
diameter of the pipe. To provide free passage for scrapers, changes in
pipeline direction are made by bending pipe rather than using elbow or
tee fittings.
Sandtraps are, in effect, sediment or settling chambers which collect
dirt, scale, sludge and floating debris pumped through the pipeline or
accumulated during pipeline cleaning. They are installed on the suction
side of each pump station. Sandtraps split the flow into two 14-inch
barrels, thus reducing the velocity of the flow. This allows sediment to
settle out. They must be cleaned periodically and after each scraper
run.
12-92
QM 5099
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