EBARA EFQT3 - Manual (Page 10)

EBARA Fluid Handling 10
If the application involves a high discharge
head, gradually close the discharge throttling
valve before stopping the pump.
Bypass Lines
Self-priming pumps are not air compressors.
During the priming cycle, air from the suction
line must be vented to atmosphere on the
discharge side. If the discharge line is open,
and a check valve has been installed in the
discharge line, the discharge side of the
pump must be opened to atmospheric
pressure through a bypass line installed
between the pump discharge and the check
valve. A self-priming centrifugal pump will
not prime if there is sufficient static liquid
head to hold the discharge check valve
closed.
NOTE
The bypass line should be sized so that it
does not affect pump discharge capacity;
however, the bypass line should be at
least 1 inch in diameter to minimize the
chance of plugging.
In low discharge head applications (less
than 30 feet or 9 meters), it is recommended
that the bypass line be run back to the wet
well, and locate 6 inches below the water
level or cut-off point of the level pump. In
some installations, this bypass line may be
terminated with a six-to-eight foot length of
1¼ inch ID. Smooth-bore hose; air and
liquid vented during the priming process will
then agitate the hose and break up any
solids, grease, or other substances likely to
cause clogging.
A bypass line that is returned to a wet
well must be secured against being
drawn into the pump suction inlet.
It is also recommended that pipe unions be
installed at each 90º elbow in a bypass line
to ease disassembly and maintenance.
In high discharge head applications (more
than 30 feet), an excessive amount of liquid
may be bypassed and forced back to the wet
well under the full working pressure of the
pump; this will reduce overall pumping
efficiency. Therefore, it is recommended
that a EBARA Automatic Air Release
Valve be installed in the bypass line.
EBARA Automatic Air Release Valves are
reliable, and require minimum maintenance.
See AUTOMATIC AIR RELEASE VALVE in
this section for installation and theory of
operation of the Automatic Air Release
Valve. Contact EBARA for selection of an
Automatic Air Release Valve to fit your
application.
If the installation involves a flooded suction
such as below ground lift station. A pipe
union and manual shut-off valve may be
installed in the bleed line to allow service of
the valve without shutting down the station,
and to eliminate the possibility of flooding. If
a manual shut-off valve is installed
anywhere in the air release piping, it must be
a full-opening ball type valve to prevent
plugging by solids.
If a manual shut-off valve is installed in a
bypass line, it must not be left closed
during operation. A closed manual shut-
off valve may cause a pump which has
lost prime to continue to operate without
reaching prime, causing dangerous
overheating and possible explosive
rupture of the pump casing. Personnel
could be severely injured.
Allow an over-heated pump to cool before
servicing. Do not remove plates, covers,
gauges, or fittings from an overheated
pump. Liquid within the pump can reach
boiling temperatures, and vapor pressure
within the pump can cause parts being
disengaged to be ejected with great force.
After the pump cools, drain the liquid from
the pump by removing the casing drain plug.
Use caution when removing the plug to
prevent injury to personnel from hot liquid.
CAUTION!
CAUTION!
DANGER!