Page 195 - Shale Shakers Drilling Fluid Systems
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CHAPTE R ELEVE N
Centrifugal Pumps
Many types of pumps move fluids in the oil • Slow operating speeds (50 to 130 rpm)
field. Pumps may lift fluid, force it into pressure • Uses various drives—belt, chain, or geared
vessels, or flow it through pipes. Regardless of
pump design, horsepower requirements increase A rotary pump is simple in design, has few
with the specific gravity of any fluid. Although moving parts, and, like a reciprocating pump, also
centrifugal pumps are used extensively in drilling uses positive displacement. A rotary pump consists
fluid systems and will be the primary focus of this primarily of two meshed cams, or gears (the idler
chapter, other available pumps are briefly de- and the drive gear), in a tight-fitting casing. The
scribed below. drive gear is connected to the power supply and
its rotation drives the idler gear. Liquid fills the
spaces between the gear teeth and, as they rotate,
COMMONLY USED OIL FIELD PUMPS
the liquid is literally "squeezed" out the discharge.
As the gear teeth then separate, a partial vacuum
A reciprocating pump is a positive-acting, dis-
is created causing liquid to continuously fill the
placement pump, which creates flow by displac- pump chamber from the suction side.
ing liquid from a cylinder or cavity with a moving Rotary pumps including gear, screw, deformed
member, or piston. Each chamber, or cylinder, is vane, sliding vane, axial-piston, and cam type are
filled and emptied by the mechanical motion of a
piston that alternately draws-in and then expels used when discharge pressures of 500 to 1000 psi
or greater are needed. A rotary pump produces a
liquid. Available horsepower and the strength of continuous flow regardless of line backpressure
the pump's structural parts determine pressure and should not be used to pump erosive slurries.
capabilities. Volume, or capacity, delivered per
Because of close clearances and metal-to-metal
stroke by a reciprocating pump is constant regard- contact by the gear teeth, rotary pumps work best
less of pressure. The flow rate varies with changes
in piston speed, the diameter of the cylinder in when handling solids-free liquids with adequate
lubricating qualities. These pumps are particularly
which the piston moves, and the stroke length of adept at pumping liquids with high viscosity or
the piston. Most reciprocating pumps use multiple low-vapor pressures. They can be used to move
cylinders (i.e., duplex, triplex, etc.) to regulate the
pulsating flow generated by the reciprocating mo- small capacities at medium discharge heads and
where high suction lift is required. Applications
tion. They are used primarily on drilling rigs as include oils or viscous materials such as soaps,
mud and cement pumps. Centrifugal or rotary
pumps, except for special applications, have re- molasses, tars, and paints.
Rotary pumps offer the following features:
placed small reciprocating pumps, although they
are still used where their variable-speed, stroke, • Positive displacement
and piston cylinder combinations are important • Self-priming (up to 22 feet suction lift)
considerations. High torque and decreasing effi-
ciencies where solid abrasives are present in the • Low speed—spur types—up to 300 rpm
fluid are major disadvantages of this type of pump. • Medium speed—herringbone type—up to
Reciprocating pumps offer the following features: 1750 rpm
• Uses various drives—belt, chain, geared, or
• Positive displacement directly coupled to motor
• Self-priming
• Pressure limited only by pump strength and Diaphragm pumps are classed also as positive
motor capacity displacement pumps. The diaphragm acts as a
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