By definition, NPSH means: “net
positive suction head” above the vapor
pressure of the pumped liquid available
at the centerline of the pump. It should
always be given in feet of pumped
liquid. The NPSH is actually a mea-
surement of the amount of energy
available in the pumped liquid to
produce the required absolute entrance
velocity in the pump. If a pump
requires more energy (or NPSH) than is
available at a given capacity, the
pressure at the inlet will fall below the
vapor pressure of the pumped liquid
and loss of performance will result as
the liquid vaporizes.
P
s
= Pressure in the suction vessel in
PSIA.
P
vp
= Vapor pressure of the pumped
fluid in PSIA.
H
s
= Static height of the pumped fluid
above (+) or below (-) the centerline of
the pump in feet.
H
f
= All friction losses from the vessel
to the pump in feet.
NPSH = 2.31( )+ H
s
- H
f
For boiling liquids, P
s
and P
vp
are equal.
This item then becomes zero and can
be omitted from the equation.
1D6 Noise
Page 503
Regenerative turbine pumps typically
produce a high pitched whine that
increases in intensity as the differential
pressure produced in the pump increas-
es. While high frequency sound is
attenuated more easily than lower
frequencies, piping structures and the
fluids in them readily transmit noise.
Motors, bearings, and other rotating
components add to the noise and
sometimes create objectionable harmon-
ics.
Adequate support for the inlet and
discharge piping is important for noise
reduction.
1D7 Freezing
When ambient temperatures drop below
the freezing point of the fluid in a pump,
consideration should be given to heating,
insulating, or draining the pump. If you
choose to drain the pump, and it will only
be for a short period, first remove the
drain plugs, then drain the inlet and outlet
lines. Carefully blow out the pump with
compressed air to clear all internal
cavities of fluid.
1E Recommended Spare Parts
FOR CRITICAL SERVICES - a duplex
installation, with two identical pumping
units in parallel, is the safest and many
times the most cost effective choice.
P
s
- P
vp
sp. gr.
FOR IMPORTANT SERVICES - a
standby pump, ready for installation is
advised.
Special pricing and new pump warranty
is offered for factory rebuilding. Turn
around time can be as short as one or
two days for standard models.
FOR ROUTINE MAINTENANCE - only
the mechanical seals and a complete
set of “O” ring gaskets are recommend-
ed. Should additional components
show wear, they are available from
stock at the factory.
FOR SERVICING A PUMP THAT
DOES NOT PRODUCE RATED HEAD
- mechanical seals, “O” ring gaskets,
impeller, motor bracket, and cover.
FOR REBUILDING A PUMP - all the
components required for servicing, plus
bearings, shaft, and drive keys for
flexible coupled pumps, should be
obtained. A factory rebuild should be
considered whenever your disassembly
indicates rebuilding is necessary, as
this is usually more economical.
The factory recommendation for spare
parts are all of those listed for rebuild-
ing a pump, and are shown on the
exploded view drawings for each
individual type of pump.
Installation
2.
T41 SERIES
FLEXIBLE COUPLED PUMPS
CLOSE COUPLED PUMPS
A. Location
B. Foundation
C. Leveling
D. Alignment
E. Piping
F. Typical Installation
In order to insure that pumping
equipment is installed properly and to
obtain reliable pump operation, it is
recommended that only experienced,
qualified erecting engineers undertake
this task. Read the instructions
thoroughly before beginning.
2A Location
The first consideration for locating a
pump is elevation. The lowest possible
elevation using the shortest possible
suction piping is usually the best.
Questions regarding possible locations
should be resolved by making inlet
head calculations including all friction
losses. The one producing the highest
inlet pressure should be selected. One
reason for this precaution is that, the
greater the inlet pressure, the less
likelihood of NPSH problems. Also, a
flooded suction is particularly helpful on
start-up when the seals or the entire
pump can be ruined because it is not
properly primed and purged of air.
A dry, easily accessible location is also
important. Allow ample clearance around
the unit for free air circulation. If a dry
location is not available, the pump can be
mounted on a foundation, above the floor.
Specify motor enclosure, pump materials,
or coatings to suit the worst conditions
expected. Place the pump so that it can
be easily inspected and serviced during
operation. Sufficient head room should
be provided, particularly when lifting
devices will be used for heavier assem-
blies.
2B Foundation
Baseplates alone are not rigid enough to
maintain alignment of the unit. The pump
foundation is used as a support for the
baseplate to maintain alignment of the
unit. If the baseplate is to be grouted to
the foundation, it is only necessary to
embed the edges. It is unnecessary to
completely fill under the baseplate. DO
NOT grout the unit to the foundation
until it has been properly aligned.
The foundation must be a permanent
rigid installation of concrete or other
material of sufficient mass to absorb all
normal vibrations. Locate the founda-
tion bolts using a layout or template in
relation to the suction and discharge
piping. If concrete is being used,
foundation bolts of the specified size
can be enclosed in a pipe sleeve two to
three diameters larger than the bolts to
compensate for minor variations in
alignment.
Close coupled pumps can be mounted
on a steel base prior to installation or
mounted directly to the foundation.
Place shims under one or more of the
motor
