
OM--01040TSERIES
PAGE B -- 5INSTALLATION
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-
phericpressurethrougha bypasslineinstalledbe-
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 (25,4 mm) in di-
ameter to minimize the chance of plugging.
Inlow 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 of1 1/4 inch I.D.smooth-borehose;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 is returned to a wet well
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 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
Valve to fit your application.
Iftheinstallationinvolvesafloodedsuctionsuchas
abelow-groundliftstation.Apipeunionandmanu-
alshut-offvalve maybe installedin thebleed lineto
allowserviceofthevalvewithoutshuttingdownthe
station, and to eliminate the possibility of flooding.
If a manual shut-off valve is installed anywhere in
theair release piping, it must beafull-openingball
type valve to prevent plugging by solids.
If a manual shut-off valve is installed in a by-
pass line, it must not be left closed during oper-
ation. A closed manual shut-off valve may
cause a pump which has lost prime to continue
tooperatewithoutreachingprime,causingdan-
gerous overheating and possible explosive
rupture of the pump casing. Personnel could be
severely injured.
Allow an over-heated pump to com-
pletely cool before servicing.Do not re-
move plates, covers, gauges, orfittings
from an over-heated pump. Liquid with-
in the pump can reach boiling tempera-
tures, and vapor pressure within the
pump can cause parts being disen-
gaged to be ejected with greatforce. Af-