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IJ PUMP OPERATION AND MAINTENANCE MANUAL

BO2660-01 1-4

on the outboard shaft seal as well as the pressure reducing sleeve. It also serves to transfer leakage
past the drum to the suction system.

1.2.4 MINIMUM FLOW

Another phenomenon of the multi-stage pump is for the temperature of the liquid to rise progressively
as it is pushed through the pump. If flow is reduced below the minimum required, then overheating
and flashing may occur, causing severe damage to the pump. The plant's minimum flow system
should ensure that the flow is kept at or above minimum, bypassing to suction the flow necessary to
prevent overheating and flashing.

1.2.5 MINIMUM FLOW ORIFICE

The minimum flow orifice is furnished with the pump for integration in the plant's piping. Design of
the orifice is based on the differential of the pump minus the line loss in the plant's piping. Thus, the
orifice is peculiar to each pump as well as the system in which it functions.

1.2.6 NET POSITIVE SUCTION HEAD

Centrifugal pumps also require Net Positive Suction Head (NPSH) for proper operation. This is
reflected in the pump's characteristic curve. When changing plant conditions that affect NPSH,
inattention to these curves is likely to cause damage to the pump; in fact, this is a major cause of
failure. For example: Throttling inlet pressure back to a point on a curve that is below the required
NPSH will cause cavitation in the inlet eye resulting in immediate and major damage to the internal
assembly of the pump.

1.2.7 SHAFT SEAL

In your pump, shaft sealing is provided by a mechanical seal. A mechanical seal is a precision device
in which the face of a mating ring on the shaft sleeve rotates against the face of a primary ring on the
seal housing. The sealing faces are highly polished and run with a very thin film of cooling liquid.
The seal is loaded by spring and hydraulic forces pushing against the mating ring. A seal flush system
is employed to keep the mechanical seal at a nominal temperature.

1.2.8 COOLING WATER SYSTEM

A plant-equipped cooling water system circulates water through the oil cooler, seal flush, stuffing
box, and/or pump pedestal, helping to maintain the temperature of these components at the acceptable
level for satisfactory operation.

1.2.9 LUBE OIL SYSTEM

The lube oil system is an integral unit of your pump. A pump mounted on the pump shaft or on the
baseplate pumps lube oil from the baseplate-mounted reservoir, through supply lines and the oil
cooler, to the pump bearings; the hot oil then drains back into the reservoir. The system may also
include thermometers, pressure gauges, pressure switches, relief valves, an auxiliary oil pump, and a
filter.

1.2.9.1 Auxiliary Oil Pump

The auxiliary lube oil pump is furnished to provide lubrication for startup, post-operation, and in the
event that the main oil pump fails. This pump is driven independently but it pumps from the same
reservoir as the main lube oil pump.