Instruction and Operation Manual
SA-07-11-37 Rev Orig
10
Jan 2009
OPERATION & CONTROL
Operation of Sundyne Pumps
Under normal operation, several factors must be
taken into consideration to ensure successful
pump operation. Experienced pump operators
will be aware of jeopardizing factors and their
effects.
Suction Conditions
Improper flow of liquid into the impeller is the
most common operational abuse of centrifugal
pumps. Two conditions must exist to prevent
turbulence at the eye of the impeller.
See suction piping section.
Liquid reaching the impeller eye must
have enough vapor pressure to prevent
the fluid from flashing to a gas in the
impeller. If this condition occurs, it will
cause cavitation, which can damage the
impeller and inducer. When centrifugal
pumps cavitate the noise sounds like
the pump is “pumping gravel”. In high
speed, single stage pumps, this sound
may not be discernable. Cavitation can
be prevented by maintaining suction
pressure at a high enough level and
suction temperatures low enough to
maintain Net Positive Suction Head
(NPSH) available greater than Net
Positive Suction Head (NPSH) required
by the pumps.
Minimum Flow Conditions
Vibration and noise will occur during operation of
centrifugal pumps if either of two conditions
exist:
•
Internal flow separations
•
Recirculation at low flow conditions.
If the operator is noticing excessive noise or
vibration, operation must be suspended until the
cause is determined and corrected. Continued
use may cause damage to the pump.
Resonance in the discharge line can accentuate
noise, vibration, and damage to the pump,
primarily when a control valve is located an
excessive distance downstream from the pump.
Entrained Gases
The head and capacity of centrifugal pumps will
be reduced by gas that is drawn in with the
liquid. Under normal operating conditions,
centrifugal pumps can tolerate up to 2% of gas
(by volume). Entrained gases can cause
damage to mechanical seals with the exception
of double seals. If you have entrained gas,
contact Sundyne for further instruction.
System Head Curve
The point of intersection between the system
curve and the pump characteristic curve
determines the flow or operation for the
centrifugal pump. For steady flow to occur, the
system curve must intersect the pump
characteristic curve at a significant angle. The
following diagram gives examples of satisfactory
and unsatisfactory angles of intersection.
Figure 2. Typical Operation
Note: The curve for pump A has a significant
angle of intersection with system curves
D and E. The system curve D could
represent a system with the control
valve wide open while system E could
represent the same system but with the
throttle valve closed to reduce flow from
flow 1 to flow 2. Pump curve B, on the
other hand, will provide only flow 2,
even with the control valve wide open
(curve D). When the control valve is
partially closed to create system curve
E, the curve E and lower pump curve B
are practically parallel. The lack of a
significant angle of intersection means
