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SELF-PRIMING CENTRIFUGAL PUMPS OM--04760
PAGE B -- 5INSTALLATION
minimize the chance of plugging.
In low discharge head applications (less than 30
feet or 9 meters), it is recommended that the by -
pass line be run back to the wet well, and located 6
inches below the water level or cut-off point of the
low level pump. In some installations, this bypass
line may be terminated with a six-to-eight foot
length of 1 1/4 inch I.D . smooth-bore hose; airand
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 i s returned to a wet well
must be secured against being drawn into
the pump suction inlet.
It is also recommended that pipe unions be in-
stalled at each 90_ 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 by-
passed and forced back to the wet well under the
full working pressure of the pump; this will reduce
overall pumping efficiency. Therefore, it is recom-
mended that a Gorman-Rupp Automatic Air Re-
lease Valve be installed in the bypass line.
Gorman-Rupp Automatic Air Release Valves are
reliable, and require minimum maintenance. See
AUTOMATIC AIR RELEASE VALVEin this section
for installation and theory of operation of the Auto-
matic Air Release Valve. Consult your Gorman-
Rupp distributor, or contact the Gorman -Rupp
CompanyforselectionofanAutomaticAirRelease
V alve to fit your application.
If the installation involves a floodedsuction such as
a below-ground lift station, a pipe union andmanu-
al shut-off valve may be installed in the bleed line to
allow serviceof thevalve 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-openingball
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 with-
out reaching prime , causing dangerous
overheating and possible explosive
rupture of the pump casing. P
ersonnel
could be severely injured.
Allow an over-heated pump to cool be-
fore servicing. Do not remove plates,
covers, gauges, or fittings from an over-
heated pump. Liquid within the pump
can reach boiling temperatures, and va-
por 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 re-
moving the casing drain plug. Use cau -
tion when removing the plug to prevent
injury to personnel from hot liquid.
AUTOMATIC AIR RELEASE VALVE
When properly installed and correctly adjusted to
the specific hydraulic operating conditions of the
application, the Gorman-Rupp Automatic Air Re-
leaseValvew illpermit air to escape through the by-
pass line, and then close automatically when the
pump is fully primed and pumping at full capacity.
Theory of Operation
Figures 2 and 3 show a cross-sectional view of the
Automatic Air Release Valve, and a corresponding
description of operation.