This procedure will flush residue
from the close fitting impeller
surfaces. If not immediately
successful, refer to Section 1, 1C
Placing Stored Pumps Into Service.
Because of the large areas of close
fitting surfaces inside these pumps,
it takes only microscopic residue to
produce substantial resistance to
rotation. Once loosened, this
material is quickly dispersed and
the impellers find their hydraulic
center. If these procedures are
followed carefully, no damage will
result from "breaking loose" the
impeller.
3F Cooling Water
When the pump is used to transfer
hot fluids, consideration should be
given to cooling the seals and/or
selecting materials that will give
satisfactory seal life. The actual
temperature at the seal faces, the
most critical area, will always
exceed the surrounding fluid
temperature. If seal flushing lines
have not been installed, heat can
build up on the seal faces to a
degree that may destroy the fluid
film necessary to prevent rapid
wear. In some cases it is neces-
sary to cool the seal flushing fluid.
Refer to the seal manufacturers
charts for guidance, or to selection
data in the MTH catalog, any time
fluids can reach or exceed their
boiling point.
3G Priming
Pumps should not be operated
unless they are completely filled
with liquid. Damage to parts of the
pump that depend on liquid for their
lubrication can occur.
Impellers can seize quickly when a
pump is run dry. Without lubrica-
tion, seal faces can be damaged
from heat buildup. Pumps can be
easily primed with a vacuum pump.
An ejector or liquid ring vacuum
pump is recommended because
they are not damaged if liquid
enters them. Connect the vacuum
line to the discharge side of the
pump, either in the discharge
opening or the drain tap. A foot
valve is not necessary when this
kind of device is used. When a
vacuum pump is not practical, a
foot valve in the suction inlet can be
used to prevent liquid from running
out. The pump and suction line can
then be filled completely from an
outside source. A vent opening will
be necessary during filling to let air
escape. A tight foot valve will keep
the pump constantly primed so that
automatic operation is possible.
The valve should be inspected
regularly to see that it does not
develop leaks, allowing the pump to
run dry. Optional self-priming
casings are available for MTH
pumps allowing priming when a
vacuum pump or foot valve is not
practical. Refer to specific literature
for details.
There are four components to the
self primer:
1. A check valve - necessary to
maintain a vacuum in the suction
line as surging occurs in the
pump.
2. An air eliminator - used on the
discharge side of the pump to
separate air from liquid so the
liquid can be used again as air is
carried through the pump.
3. A recirculating line - carries liquid
from the air eliminator to the
suction.
4. A fluid chamber - used on the
inlet side to provide a supply of
fluid to speed up priming.
Small suction lines are desirable to
minimize priming time.
Using the self priming casing, it is
only necessary to:
1. Open the plugs in both the inlet
and discharge chambers.
2. Pour fluid in one until both are
full.
3. Tighten both plugs.
4. Turn on the pump.
Priming time depends on lift,
volume of air in the suction line, and
the size of the regenerative turbine
pump used. If priming time is long
and the pump becomes warm, refill
the priming chambers with fresh
liquid. Most turbine pumps will
pump twenty-six to twenty-eight
inches of mercury vacuum with cold
water in the pump, but have very
little capacity and therefore are not
practical at lifts over twenty-two
feet.
The best way to prime a pump and
keep it primed is to use a flooded
suction. While this is not always
practical, it does provide a number
of advantages. The likelihood of
pump damage from dry running is
eliminated. Suction lines may be
large, reducing line losses and
minimizing the potential of cavita-
tion damage. There are no check
valves or priming devices to fail or
require maintenance. Whenever
possible, design pumping systems
with a flooded suction.
3H Starting
Before starting a pump for the first
time, be sure that all the preceding
operations have been carried out.
Proper rotation, priming, and a free
turning pump are most important.
1. Start the pump with the minimum
possible line restriction.
2. Open discharge valves before
pressing the starter.
3. Start the pump and let the
system clear of air.
4. Listen for foreign material being
carried through the pump.
5. Slowly close necessary valves or
otherwise place the pump into
service.
6. Listen for indications of undue
load or other sounds indicating
problems.
7. Use a clip-on ammeter to check
for a steady load after approxi-
mately fifteen minutes of
operation.
3I Stopping
It is best to stop the pump with the
least discharge head possible both
for minimizing strain on compo-
nents, and to be in low power mode
in anticipation of restarting. If the
pump will be down for more than a
few weeks it is advisable to drain it.
Follow the instructions for long term
storage, Section 1 , 1B Storage.
After any prolonged stoppage, turn
the pump over by hand before
restarting, to be sure it is free.
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