EBARA EFQT8 - Manual (Page 10)

EBARA Fluid Handling 9
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 an 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
Fluid Handling 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.
DANGER!
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!
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 1 ¼ 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.
CAUTION!
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.