
OM--01930--03TSERIES
PAGE B -- 5INSTALLATION
friction losses. Never install a throttling valve in a
suction line.
Withhighdischargeheads,itisrecommendedthat
a throttling valve and a system check valve be in-
stalled in the discharge line to protect the pump
from excessive shock pressure and reverse rota-
tion when it is stopped.
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. Dur-
ing 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 will be vented
through the discharge. However, if a check valve
has been installed in the discharge line, the dis-
chargesideofthepumpmustbeopenedtoatmos-
phericpressurethroughabypasslineinstalledbe-
tween 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 dis-
charge check valve closed.
NOTE
The bypass line should be sized so that it does not
affect pump discharge capacity; however, the by-
pass line should be at least 1 inch in diameter to
minimize the chance of plugging.
Inlow discharge head applications (less than 30
feet),itisrecommendedthatthebypasslineberun
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
beterminatedwithasix-to-eightfootlengthof11/4
inch I.D. 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.
Abypasslinethatisreturnedtoawetwell
must be secured against being drawninto
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 willreduce
overallpumpingefficiency.Therefore,itisrecom-
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 AIRRELEASE VALVE in 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
Valve to fit your application.
If theinstallationinvolvesa floodedsuctionsuchas
abelow-groundliftstation.Apipeunionandmanu-
alshut-offvalvemaybe installedinthebleedlineto
allowserviceofthevalvewithoutshuttingdownthe
station, and to eliminate the possibility of flooding.
If a manual shut-off valve is installed anywhere in
theairrelease piping, itmustbeafull-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
duringoperation.Aclosedmanualshut-
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. Personnel
could be severely injured.
Allow an over-heated pump to cool be-
fore servicing.Do not remove plates,