Section
E41•T41
Page 503
Dated
June 2016
97-4622-01-588
the fluid source. It should be the
same size as the pump inlet or sized
based on reasonable fluid friction
losses.
A foot valve is recommended when
lifting fluid from a sump. This will
save wear and tear on any pump,
even those equipped with self prim-
ing capability.
A strainer is recommended imme-
diately ahead of the pump on any
newly constructed system if there is a
possibility that foreign material large
enough to damage pump clearances
may remain even though the piping
has been flushed.
Valves in the outlet piping of a regen-
erative turbine pump should always
be open 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
starting any pumping system. With-
out some fluid in the pump, it can gall
and lock up the impellers. Violent
pump failure will result from contin-
ued operation with the inlet valve
closed.
1D4 Priming
Regardless of whether self-priming
equipment is used or not, always fill
the pump and vent it of air before
starting, for best seal and pump life.
Under most circumstances, regener-
ative turbine pumps can be made to
self-prime as long as a small amount
of fluid can be recirculated through
the impeller and the fluid 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 representa-
tive.
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 increasing NPSH is to
raise the static head on the pump in-
let, (H
s
). 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 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 pres-
sure 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 equa-
tion.
1D6 Noise
Regenerative turbine pumps typically
produce a high pitched whine that
increases in intensity as the differen-
tial pressure produced in the pump
increases. 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
harmonics.
Adequate support for the inlet and
discharge piping is important for
noise reduction.
1D7 Freezing
When ambient temperatures drop be-
low 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 effec-
tive choice.
FOR IMPORTANT SERVICES - a
standby pump, ready for installation
is advised.
Special pricing and new pump war-
ranty 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 - 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 disassem-
bly indicates rebuilding is necessary,
as this is usually more economical.
The factory recommendation for
spare parts are all of those listed for
rebuilding a pump, and are shown on
the exploded view drawings for each
individual type of pump.
P
s
- P
vp
sp. gr.
