Page 503
as far as possible when the pump is
started. This will reduce the start-up load
on the pump and motor.
Never start the
pump with the discharge valve closed.
Inlet valving should be open when start-
ing any pumping system. Without some
fl uid in the pump, it can gall and lock up
impellers.
Violent pump failure will
result from continued operation with
the inlet valve closed.
1D4 Priming
Regardless of whether self-priming
equipment is used or not, always fi ll the
pump and vent it of air for best seal and
pump life. Under most circumstances,
regenerative turbine pumps can be made
to self-prime as long as a small amount
of fl uid can be recirculated through the
impeller and the fl uid doesn’t heat up
noticeably.
1D5 NPSH (Net Positive Suction Head)
The NPSH required varies with every
size and capacity of pump. The NPSH
required by your unit can be obtained
from the performance curves or from
your MTH representative.
If the NPSH available is not equal to or
greater than that required by the pump,
it must be increased or a different pump
selected. The usual method for increas-
ing NPSH is to raise the static head on
the pump inlet, (H
s
).
By defi nition, 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 measurement 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.
P
s
= Pressure in the suction vessel in
PSIA.
P
vp
= Vapor pressure of the pumped fl uid
in PSIA.
H
s
= Static height of the pumped fl uid
above (+) or below (-) the centerline of
the pump.
H
f
= All friction losses from the vessel to
ff
the pump.
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
Regenerative turbine pumps typically pro-
duce a high pitched whine that increases
in intensity as the differential pressure
produced in the pump increases. While
high frequency sound is attenuated more
easily than lower frequencies, piping
structures and the fl uids in them readily
transmit noise. Motors, bearings, and
other rotating components add to noise
and sometimes create objectionable
harmonics.
Careful pump installation can contribute
to noise reduction. Proper alignment of
the pump and driver is essential.
Adequate supports for the inlet and
discharge piping is equally important.
A degree of noise reduction may be
obtained when the pumping unit is sup-
ported free of building structures by the
use of vibration isolators, fl exible piping
and conduit connections. Elastomer type
couplings are the best choice to separate
motor noises from the fl uid and piping
structure.
1D7 Freezing
When ambient temperatures drop below
the freezing point of the fl uid in a pump,
consideration should be given to heating,
P
NPSH = 2.31( )+ H
NPSH = 2.31( )+ H
NPSH = 2.31( )+ H
NPSH = 2.31( )+ H
- P
NPSH = 2.31( )+ H
NPSH = 2.31( )+ H
NPSH = 2.31( )+ H
NPSH = 2.31( )+ H
sp. gr.
NPSH = 2.31( )+ H
NPSH = 2.31( )+ H
NPSH = 2.31( )+ H
insulating, or draining the pump. If you
choose draining the pump, and it will
only be for a short period, fi rst remove
the drain plugs and drain the lines to and
from the pump. Carefully blow out the
pump with compressed air to clear all
internal cavities of fl uid.
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.
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 recommended.
Should additional components show
wear, they are available from stock at the
factory.
FOR SERVICING A PUMP THAT DOES
NOT PRODUCE RATED HEAD - me-
chanical 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 fl exible
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 needed for
rebuilding a pump and are shown on
the exploded view drawings for each
individual type of pump.
T31 SERIES
Installation
CLOSE COUPLED PUMPS
FLEXIBLE COUPLED PUMPS
A.
Location
B.
Foundation
C.
Leveling
D.
Alignment
E.
Piping
In order to insure that pumping equip-
ment is installed properly and to obtain
reliable pump operation, it is recom-
mended that only experienced, qualifi ed
erecting engineers undertake this task.
Read the instructions thoroughly before
beginning.
2A Location
The fi rst 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
fl ooded 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.
2.
