Page 212 - Shale Shakers Drilling Fluid Systems

194 SHALE SHAKERS AND DRILLING FLUID SYSTEMS

FIGURE 11-6. Plot "f" values vs. Reynolds number.

example, in a 6-inch line, two butterfly valves water, have viscosities above 500 centistokes.
and one welded branched tee (4 ft + 4 ft + 28 ft) Therefore, specific gravity and viscosity are inde-
would add the equivalent of 36 feet of 6-inch pipe pendent of one another, as are their effect on
to the length of actual pipe connected to the cen- pump performance and power requirements.
trifugal pump.
Measuring Viscosity
PUMPING VISCOUS LIQUIDS
Viscosity is expressed in absolute or kinema-
tic units:
When centrifugal pumps handle viscous fluids,
the viscosity must be considered. Viscous, or thick,
liquids are not handled as easily as water, particu-
larly by centrifugal pumps. The internal friction
losses increase, thereby reducing capacity, head, and Saybolt viscometers are most common and viscos-
efficiency, and requiring even greater horsepower. ity is frequently expressed in "Saybolt Seconds."
A pump operating at a lower speed is less af- The time for a measured volume of fluid to flow
fected by viscosity and lift requirements than if it through an orifice of specified dimensions is cal-
were operated at higher speeds. Viscous slurries culated in seconds and is called the SSU or SSF
should flow to the pump suction by gravity or (Saybolt Seconds Universal or Saybolt Seconds
under positive pressure to ensure proper filling of Furol) depending on orifice size.
the pump. Other viscometers, such as Redwood, Irany,
Liquids that have high specific gravities are not and Zahn, operate on the same principle. The
necessarily viscous. For example, mercury has a Ostwald, Bingham, and Ubbelohde viscometers
high specific gravity of 13.7, however, its viscos- use a capillary tube in place of an orifice to mea-
ity is only 0.118 centistokes. Water, at standard sure fluids of lower viscosity.
temperature, has a viscosity of 1.0 centistokes, and A Brookfield viscometer measures the torque on
transmission lubricants, which are lighter than a disc rotating in the fluid. The spring, which