JETStream 3000 series, Operation Manual, Page: 18 / 84

Operation Manual
10
Technical Notes
*** Driver selection and coupling selection requires
engineering analysis of torsional loads and vibra-
tions (TVA). Jetstream can supply the mass- elastic
data for the pump but it is customer’s responsibil-
ity to perform TVA of the system. Coupling failure,
engine damage, and powerend damage can result
from incorrect coupling selection.
****All pumps have a minimum inlet pressure neces-
sary to prevent cavitation.
Additionally, Jetstream (and many other) pumps
have a maximum allowable inlet pressure. Excessive
inlet pressure will not affect the operation or life of
the fluid end, but can negatively affect the power
end.
The connecting rods are equipped with plain bear-
ings where they contact the crankshaft. These bear-
ings require lubrication to survive. When the crank-
shaft rotates and pulls the crosshead backwards
through the suction stroke, the force between the
connecting rod journal bearing and the crankshaft
decreases greatly. This reduction in force and the
rotation of the crankshaft causes oil to be drawn into
the small space between the connecting rod journal
bearing and the crankshaft. As there is no oil pump
in the 3000/3600/4200 series, this is the only mecha-
nism that lubricates the journal bearings.
High pressure on the plungers during the suction
stroke can prevent oil from being drawn into the
space between the connecting rod journal bear-
ing and the crankshaft. The lack of lubrication can
cause journal bearings to fail in only a few hours.
This problem is worse with large plungers, high inlet
pressure, and low speeds.
Following Jetstream’s maximum allowable fluid end
inlet pressure of 75 psi and minimum pump speeds
of 200 rpm for the 3000, 183 rpm for the 3600, 173
rpm for the 4200, and 100 rpm for the 6000 series
will prevent this type of failure.