9
Siphoning
Do not terminate the discharge line at a level lower than of the liquid being pumped
unless a siphon breaker is used in the line. Otherwise, a siphoning action causing
damage to the pump could result.
VALVES
If a throttling valve is desired in the discharge line, use a valve as large as the largest
pipe to minimize friction losses. Never install a throttling valve in a suction line.
With high discharge heads, it is recommended that a throttling valve and a system
check valve be installed in the discharge line to protect the pump from excessive shock
pressure and reverse rotation when it is stopped.
5. DISCHARGE LINES
If the application
involves a high discharge head, gradually close the
discharge throttling valve before stopping the pump.
CAUTION!
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, this air 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 an 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 25mm in
diameter to minimize the chance of plugging.
In
low discharge head applications
(less than 9 meters), it is recommended that the
bypass line be run back to the wet well, and locate 150mm below the water level or cut-
off point of the level pump. In some installations, this bypass line may be terminated
with a 1800-2400mm length of 32mm 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.
CAUTION!
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 9 metres), 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 Automatic Air Release Valve be installed in the bypass
line
.
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 your Remko distributor for
selection of an Automatic Air Release Valve to fit your application.