Page 230 - 4637

satisfactory. The modifications that have le to success are: (1) use
of slush pump type of valves, (2) substitution of liners and half
pistons for plungers and packing, (3) charging of the suction
pressure.
In some earlier triplex slush pumps, efforts were made to
operate without a charge pump. In this instance, conventional slush
pump pistons were used. Atmospheric pressure alone on the back
side of the piston, on the suction stroke, was inadequate to expand
the conventional piston sufficiently to obtain an effective seal
between piston and liner. Expediency dictated the use of a
centrifugal charge pump to assure no cavitation in the triplex slush
pump operation. A piston "may be developed in the future with a
seal on the back side that will operate effectively at atmosphere
pressure.
As of this date all five of he larger American manufactures
of rotary drilling machinery are offering a lie of triplex slush
pumps, ranging in input capacities from 275 hp to 1700 hp.
Typical pumps of this basic design are shown in Fig. 16.2. The
various lines of triplex slush pumps are more dissimilar than are
their respective lines of duplex double-acting slush pumps.
Triplex single-acting slush pumps have higher rating
operating speed rages than duplex double-acting slush pumps of
equal capacity. Maximum fluid end working pressures, for all
slush pumps, are included in the manufacturer's specifications.
Also the displacement, at various combinations of speed and liner
size( together with corresponding safe working pressure), is
available from the manufacturer. Routine maintenance of the
power end of either duplex or triplex pumps is minimal except that
recommended oil levels should not be overlooked.
The fluid end of a slush pump is subjected to abrasive action
of fluid being handled. This may be most severe if sand and other
solids are allowed to remain concentrated in the circulation mud
stream. Various means of removing abrasives from mud are being

229