GORMAN-RUPP PUMPS GMC Series User manual

OM-04384-05
March 18, 2021
GORMAN‐RUPP PUMPS
www.grpumps.com
2021 Gorman‐Rupp Pumps Printed in U.S.A.
INSTALLATION, OPERATION,
AND MAINTENANCE MANUAL
ROTARY GEAR PUMPS
MODELS
GMC SERIES
IRON PUMPS
Construction Code
3-B

TABLE OF CONTENTS
i
INTRODUCTION PAGE I - 1...................................................
SAFETY - SECTION A PAGE A - 1............................................
INSTALLATION - SECTION B PAGE B - 1.....................................
PUMP MODEL DESIGNATION PAGE B-1..................................................
PREINSTALLATION INSPECTION PAGE B-2................................................
STORAGE PAGE B-2....................................................................
Flushing PAGE B-2..................................................................
PUMP INSTALLATION PAGE B-3..........................................................
Lifting PAGE B-3.....................................................................
Positioning The Pump PAGE B-3......................................................
Mounting PAGE B-3.................................................................
Piping PAGE B-3....................................................................
Strainers PAGE B-4..................................................................
Gauges PAGE B-4...................................................................
Sealing PAGE B-4...................................................................
Valves PAGE B-4....................................................................
ALIGNMENT PAGE B-4..................................................................
ELECTRICAL CONNECTIONS PAGE B-4...................................................
OPERATION - SECTION C PAGE C - 1.......................................
PUMP OPERATION PAGE C-1............................................................
PRE‐OPERATION PAGE C-1..............................................................
Before Starting The Pump PAGE C-1...................................................
Checking Pump Rotation PAGE C-1...................................................
STARTING PAGE C-2....................................................................
OPERATION PAGE C-2..................................................................
Liquid Temperature PAGE C-2.........................................................
Overheating PAGE C-2...............................................................
Checking Gauges PAGE C-2..........................................................
Strainer Check PAGE C-2.............................................................
Leakage PAGE C-3..................................................................
PRESSURE RELIEF VALVE ADJUSTMENT PAGE C-3........................................
Cracking Pressure PAGE C-3.........................................................
Complete By‐Pass Pressure PAGE C-3.................................................
STOPPING PAGE C-3....................................................................
TROUBLESHOOTING - SECTION D PAGE D - 1...............................
PREVENTIVE MAINTENANCE PAGE D-4...................................................
PUMP MAINTENANCE AND REPAIR - SECTION E PAGE E - 1.................
PARTS KEY:
Typical GMC Pump Model PAGE E-2...................................................
ASSEMBLED GMC PUMP MODEL ILLUSTRATION PAGE E-4................................
PUMP DISASSEMBLY PAGE E-4..........................................................
Preparaing for Disassembly PAGE E-4.................................................
Pressure Relief Valve (10) PAGE E-5...................................................

TABLE OF CONTENTS
(continued)
ii
Coverplate Kit (11) PAGE E-5.........................................................
Head/Idler Kit (01 and 02) PAGE E-5..................................................
Backhead Kit Removal (06) PAGE E-6..................................................
Rotor/Shaft Removal (03) PAGE E-6...................................................
Seal Removal (05) PAGE E-6..........................................................
Housing Assembly (04) PAGE E-6.....................................................
PUMP REASSEMBLY PAGE E-6..........................................................
Cleaning and Inspection PAGE E-7....................................................
Bushing Preparation PAGE E-7........................................................
Housing Assembly (04) PAGE E-7.....................................................
Rotor/Shaft Assembly (03) PAGE E-7..................................................
Head/Idler Assembly (01 and 02) PAGE E-8............................................
Coverplate Kit (11) PAGE E-8.........................................................
Seal Installation (05) PAGE E-8........................................................
Backhead Kit (06) PAGE E-8..........................................................
SETTING END CLEARANCE PAGE E-8....................................................
RELIEF VALVE DISASSEMBLY PAGE E-9..................................................
RELIEF VALVE REASSEMBLY PAGE E-10..................................................
Relief Valve Installation (10) PAGE E-11................................................
SEAL APPENDIX - SECTION F PAGE F-1...................................
Standard Friction Drive And Optional 60A And 61J Mechanical Seals PAGE F-1.................
Standard Lip (And Optional 65A And 65C) Seal PAGE F-3....................................
BACKHEAD ADAPTOR APPENDIX - SECTION G PAGE G-1..................
Backhead Adaptor Removal and Installation PAGE G-2......................................
O‐RING APPENDIX - SECTION H PAGE H-1..................................

GMC SERIES OM-04384
PAGE I - 1INTRODUCTION
INTRODUCTION
Thank You for purchasing a Gorman‐Rupp pump.
Read this manual carefully to learn how to safely
install and operate your pump. Failure to do so
could result in personal injury or damage to the
pump.
Because pump installations are seldom identical,
this manual cannot possibly provide detailed in
structions and precautions for every aspect of
each specific application. Therefore, it is the re
sponsibility of the owner/installer of the pump to
ensure that applications not addressed in this
manual are performed only after establishing that
neither operator safety nor pump integrity are com
promised by the installation. Pumps and related
equipment must be installed and operated ac
cording to all national, local and industry stan
dards.
If there are any questions regarding the pump or
its application which are not covered in this man
ual or in other literature accompanying this unit,
please contact your Gorman‐Rupp distributor, or
The Gorman‐Rupp Company:
The Gorman‐Rupp Company
P.O. Box 1217
Mansfield, Ohio 44901-1217
Phone: [phone]
or:
Gorman‐Rupp of Canada Limited
70 Burwell Road
St. Thomas, Ontario N5P 3R7
Phone: [phone]
For information or technical assistance on the
power source, contact the power source manufac
turer's local dealer or representative.
HAZARD AND INSTRUCTION
DEFINITIONS
The following are used to alert maintenance per
sonnel to procedures which require special atten
tion, to those which could damage equipment, and
to those which could be dangerous to personnel:
Immediate hazards which WILL result in
severe personal injury or death. These
instructions describe the procedure re
quired and the injury which will result
from failure to follow the procedure.
Hazards or unsafe practices which
COULD result in severe personal injury
or death. These instructions describe
the procedure required and the injury
which could result from failure to follow
the procedure.
Hazards or unsafe practices which COULD
result in minor personal injury or product
or property damage. These instructions
describe the requirements and the possi
ble damage which could result from failure
to follow the procedure.
NOTE
Instructions to aid in installation, operation, and
maintenance or which clarify a procedure.

OM-04384GMC SERIES
SAFETY PAGE A-1
SAFETY - SECTION A
This information is specific to Gorman‐Rupp GMC
Series Rotary Gear Pumps. It applies throughout
this manual and any manual or literature ac
companying the pump.
In addition to this manual, see the separate litera
ture covering the drive unit used to operate this
pump.
Pumps and related equipment must be in
stalled and operated according to all na
tional, local and industry standards.
This manual will alert personnel to
known procedures which require spe
cial attention, to those which could
damage equipment, and to those which
could be dangerous to personnel. How
ever, this manual cannot possibly pro
vide detailed instructions and precau
tions for each specific application or for
every situation that might occur during
maintenance of the unit. Therefore, it is
the responsibility of the owner, installer
and/or maintenance personnel to en
sure that applications and/or mainte
nance procedures not addressed in this
manual are performed only after estab
lishing that neither personal safety nor
pump integrity are compromised by
such applications or procedures.
Before attempting to install, operate, or
service this pump, familiarize yourself
with this manual, and with all other liter
ature shipped with the pump. Unfamil
iarity with all aspects of pump operation
covered in this manual could lead to de
struction of equipment, injury, or death.
The standard version of this pump is de
signed to handle a wide range of light,
medium, and heavy viscosity liquid, de
pending on design and components,
and a range of temperatures when fitted
with different seals. Do not apply at
higher temperatures that the seal will
handle. Do not attempt to pump liquids
which may damage the pump or endan
ger personnel as a result of pump fail
ure; consult the factory for chemical
compatibility.
Death or serious personal injury and
damage to the pump or components
can occur if proper lifting procedures
are not observed. Make certain that
hoists, chains, slings or cables are in
good working condition and of suffi
cient capacity and that they are posi
tioned so that loads will be balanced
and the pump or components will not be
damaged when lifting. Suction and dis
charge hoses and piping must be re
moved from the pump before lifting. Lift
the pump or component only as high as
necessary and keep personnel away
from suspended objects.
After the pump has been installed, make
certain that the pump and all piping or
hose connections are secure before op
eration. Loose connections can result in

GMC SERIESOM-04384
PAGE A-2 SAFETY
damage to the equipment and serious
injury to personnel.
Never operate the pump without a pres
sure relief valve installed on the pump
or in the discharge piping. Make certain
that pump‐mounted pressure relief
valves are installed with their adjusting
ends toward the suction port. If bi‐rota
tional operation is required, a pressure
relief device must be provided for both
directions of flow. Operation without a
pressure relief valve or with an improp
erly installed relief valve could cause
the pump to explode, resulting in seri
ous injury or death to personnel.
Before attempting to open or service the
pump:
1. Familiarize yourself with this man
ual.
2. Lock out incoming power to the
drive unit to ensure that the pump
will remain inoperative.
3. Allow the pump to completely cool
if overheated.
4. Close the discharge and suction
valve (if used).
An overheated pump can cause severe
burns and injury. If overheating occurs:
1. Stop the pump immediately.
2. Allow the pump to completely cool.
3. Refer to the instructions in this
manual before restarting the
pump.
Do not remove plates, covers, gauges,
pipe plugs or fittings from an over
heated pump. Vapor pressure within the
pump can cause parts being disen
gaged to be ejected with great force. Al
low the pump to completely cool before
servicing.
This pump may be used to handle liq
uids which may cause serious illness or
injury through direct exposure or
emitted fumes. Wear protective cloth
ing, such as rubber gloves, face mask
and rubber apron, as necessary, before
disconnecting or servicing the pump or
piping.

GMC SERIES OM-04384
PAGE B-1INSTALLATION
INSTALLATION - SECTION B
Review all SAFETY information in Section A.
Pumps and related equipment must be in
stalled and operated according to all na
tional, local and industry standards.
Since pump installations are seldom identical, this
section is intended only to summarize general rec
ommendations and practices required to inspect,
position, and arrange the pump and piping. If there
are any questions concerning your specific instal
lation, contact your Gorman‐Rupp distributor or
the Gorman‐Rupp Company.
Most of the information applies to a flooded suction
installation where liquid is supplied under pres
sure.
If the pump is positioned above the liquid in a static
lift installation, information such as mounting, pip
ing configuration and priming must be tailored to
specific conditions.
These pumps are not recommended for
use with water. Some models when fitted
with specific options may be used with wa
ter; consult the factory.
PUMP MODEL DESIGNATION
Following is a description of the model numbering
system for Gorman‐Rupp rotary gear pumps.
Rotary gear pump model numbers include design
style, port size, hydraulic size and construction
code.
Typical Pump Model
GHS 1 1/2 GF 32
Design
Style
Port
Size
Hydraulic
Size
Construction
Code
Design Style: Gorman‐Rupp rotary gear pumps
are available in five basic designs:
GMC - Medium Duty - Compact
GMS - Medium Duty
GHC - Heavy Duty - Compact
GHS - Heavy Duty
GHA - Abrasive Duty
Port Size: Gorman‐Rupp rotary gear pumps are
available in port sizes from 1 to 6 inches, depend
ing on the design style. Consult your Gorman‐
Rupp distributor or the factory for additional sizes.
Hydraulic Size: The first letter in the hydraulic size
is a rotor diameter code. The second letter indi
cates tooth length.
Construction Code: Construction Codes for Gor
man‐Rupp rotary gear pumps are as follows:
Code Description
3 Iron w/Mechanical Seal(s)
4 Iron w/Packing or Lip Seal(s)
9 316 SST w/Mechanical Seal(s)
10 316 SST w/Packing or Lip Seal(s)
32 Steel w/Mechanical Seal(s)
38 Steel w/Packing or Lip Seal(s)
Theoretical Displacement: Table B‐1 indicates
theoretical displacement values for each hydraulic
size.
NOTE
Actual capacities and recommended shaft speeds
vary according to application. Consult your Gor
man‐Rupp distributor or the factory for additional
information.

GMC SERIES
OM-04384
PAGE B-2INSTALLATION
Table B‐1. Theoretical Displacement
Hydraulic
Size
Theoretical Displacement
Per Revolution
Gallons Centimeters3
DC 0.00568 21.486
DE 0.00704 26.646
GC 0.00967 36.619
GF 0.01405 53.186
GH 0.01915 72.479
GJ 0.02317 87.700
JG 0.03579 135.49
JJ 0.05159 195.28
JL 0.07078 267.94
JP 0.10078 381.48
NK 0.10665 403.71
NM 0.14173 536.51
NP 0.17681 669.31
RM 0.24030 909.65
RP 0.29979 1134.8
RR 0.35927 1360.0
RS 0.41876 1585.1
SR 0.65752 2489.0
SU 1.10240 4173.2
TU 1.91280 7240.7
PREINSTALLATION INSPECTION
The pump assembly was inspected and tested be
fore shipment from the factory. Before installation,
check for damage which may have occurred dur
ing shipment. Check as follows:
a. Inspect the pump assembly for cracks, dents,
damaged threads, and other obvious dam
age.
b. Check for loose attaching hardware. Since
gaskets tend to shrink after drying, check for
loose hardware at the mating surfaces.
c. Carefully read all tags, decals, and markings
on the pump assembly, and perform all duties
indicated.
STORAGE
Due to the extreme close machining toler
ances within rotary gear pumps, proper
storage before installation is essential to
prevent damage to the pump.
If the pump will not be immediately installed, follow
these procedures or damage to the pump will oc
cur.
a. Do not flush the pump. Ensure that the port
plugs shipped with the pump remain in place
until piping is installed to help prevent dust or
other foreign objects from entering the pump.
b. Pumps that will not be installed for an ex
tended period should be stored indoors if
possible. The factory‐installed port plugs will
not ensure protection from excessive humid
ity, splash water or rain. In very humid or wet
conditions, install air‐tight plugs in the ports
and fill the pump completely with a lubricating
preservative liquid that is compatible with the
liquid to be pumped.
c. Pumps stored outdoors must be fully pre
served as described above, completely cov
ered with plastic or other water‐tight material,
and the covering anchored to ensure that it
will not be blown off.
Flushing
Clean piping is essential because of close‐
tolerance moving parts in this pump. Flush
all dirt, grit, weld beads or scale from the
suction piping before installing the pump.
Damage to the pump because of debris in
the suction line is not covered by the pump
warranty.
Before shipment, the pump may have been tested
using a petroleum‐based preservative. If flushing is
required, do not do so until just before installation;
the test oil protects close‐tolerance pump parts
from corrosion.
Most cleaning solvents are toxic and

GMC SERIES OM-04384
PAGE B-3INSTALLATION
flammable. Use them only in a well ven
tilated area free from flame, sparks, and
excessive heat. Read and follow all pre
cautions printed on solvent containers.
To flush the pump, use an approved solvent com
patible with the liquid being pumped. Make cer
tain that the solvent will not attack pump com
ponents, particularly seals and gaskets.
PUMP INSTALLATION
Pump dimensions are shown in the separate
Pump Specification Bulletin.
Never operate the pump without a pres
sure relief valve installed on the pump
or in the discharge piping. Make certain
that pump‐mounted pressure relief
valves are installed with their adjusting
ends toward the suction port. If bi‐rota
tional operation is required, a pressure
relief device must be provided for both
directions of flow. Operation without a
pressure relief valve or with an improp
erly installed relief valve could cause
the pump to explode, resulting in seri
ous injury or death to personnel.
Lifting
Death or serious personal injury and
damage to the pump or components
can occur if proper lifting procedures
are not observed. Make certain that
hoists, chains, slings or cables are in
good working condition and of suffi
cient capacity and that they are posi
tioned so that loads will be balanced
and the pump or components will not be
damaged when lifting. Suction and dis
charge hoses and piping must be re
moved from the pump before lifting. Lift
the pump or component only as high as
necessary and keep personnel away
from suspended objects.
Remove suction and discharge hose and piping
before attempting to lift the pump. Use lifting equip
ment with a capacity of at least five times the total
weight of the equipment being lifted.
Positioning The Pump
Locate the pump as close as possible to the liquid
being pumped. Locating the pump below the liq
uid source will help self‐priming and reduce the
possibility of cavitation.
Mounting
The pump may be shipped alone, mounted on a
base, or with pump and motor mounted on a base.
Install the pump and motor on a base before
mounting the base on a foundation.
Mount the base on a foundation that will provide
permanent, rigid support for the pump, and will be
heavy enough to absorb any vibration, strain or
shock.
Piping
Before establishing suction and discharge lines,
determine pump port positions and rotation. Fig
ure B-1 shows typical port positions for the stan
dard 180housing; if you have selected a 90
housing port option, your port positions will be dif
ferent.
Begin piping layout at the pump, and work toward
the source of supply and the point of discharge.
Either hose or rigid pipe may be used to make con
nections. If rigid piping is used, install expansion
joints to protect the pump from vibration and ther
mal expansion in the piping. Do not use expansion
joints or flexible connectors to adjust misaligned
piping.

GMC SERIES
OM-04384
PAGE B-4INSTALLATION
Housing Position Std. 180 Pump
(3-9 O'clock) Housing Mounted Relief Valve
STD.
OPT.
Rotation Clockwise
Drive End Front End
Rotation Counter-clockwise
01A S
SS DD
DD S
Figure B‐1. Typical Port Positions & Rotation
The discharge and suction lines must be inde
pendently supported to avoid vibration and strain
on the pump. For maximum pumping capacity,
keep the lines as short and straight as possible. El
bows and fittings used in the lines increase friction
losses; minimize their use. Reducers used in suc
tion lines should be the eccentric type installed
with the flat part uppermost to avoid creating air
pockets.
Before tightening a connection or flange, align it
exactly with the pump port. Never pull a pipe line
into place by tightening the flange bolts and/or
couplings.
Strainers
Because of the close‐tolerance moving parts of
this pump, it is recommended that a strainer be in
stalled in the suction line. The strainer should be
large enough to prevent excessive vacuum, and
capable of operating under high vacuum without
collapsing. The net open area of the strainer
screen depends on liquid viscosity and desired
flow rate; in any case, the sum of the area of all the
holes in the screen should be three to five times the
area of the suction pipe.
Gauges
To monitor operation and assist in troubleshooting,
a vacuum gauge and a pressure gauge should be
installed on the pump.
Sealing
Even a slight leak will affect priming, head, and ca
pacity, especially in a suction lift application. Seal
all piping joints, valves and gauges with pipe dope
or teflon tape. The sealing material should be com
patible with the liquid being pumped.
Valves
To avoid air pockets, install piping valves with the
stem horizontal.
To prevent leakage during shutdown, install a shut
off valve in the discharge line, particularly on a
flooded suction application. Shutoff valves are not
recommended for suction lines.
It is not recommended that a foot valve be installed
at the end of the suction line. If desired to install a
foot valve, consult the factory.
When handling very hot or cold liquids, install a
pressure relief valve in any part of the system that
can be valved off or isolated; this will protect piping
against damage from liquid thermal expansion or
contraction from temperature changes during
shutdown.
ALIGNMENT
Make certain that power to the drive unit
is disconnected before attempting to
connect the pump drive; otherwise, per
sonal injury may result.
NOTE
See ROTATION in Section C before mounting the
pump on the base.
Because this pump is designed to be driven by a
close‐coupled motor, it is imperative that the user
make certain that the motor drive shaft is parallel
and concentric with the rotor/shaft assembly.

GMC SERIES OM-04384
PAGE B-5INSTALLATION
ELECTRICAL CONNECTIONS
Before connecting the motor to the incoming
power, check that the electrical service available
matches the pump motor requirements stamped
on the motor nameplate.
The electrical power used to operate
this pump is high enough to cause inju
ry or death. Obtain the services of a qu
alified electrician to make all electrical
connections.
Do not install and operate a non‐explo
sion proof motor in an explosive atmo
sphere. Install, connect, and operate
the motor in accordance with The Na
tional Electric Code and all local codes.
If there is a conflict between the instruc
tions in the manual accompanying the
unit and The National Electric Code or
the applicable local code, The National
or local code shall take precedence.

OM-04384GMC SERIES
PAGE C-1OPERATION
OPERATION - SECTION C
Review all SAFETY information in Section A.
Follow the instructions on all tags, labels and
decals attached to the pump.
PUMP OPERATION
Pressure relief valves are designed to
operate as safety devices and should
never be used to regulate liquid flow.
Otherwise, the pump or piping may ex
plode and cause personal injury or
death.
PRE‐OPERATION
Make certain that all instructions in INSTALLA
TION, Section B have been carried out.
The standard version of the pump is de
signed to handle a wide range of light, me
dium, and heavy viscosity liquids, depend
ing on design and components. Do not in
stall the pump in a service with higher liquid
temperatures than what it was designed;
otherwise, pump components and opera
tion may be affected. For temperature
range consult The Gorman‐Rupp Compa
ny.
Before Starting The Pump
Never operate the pump against a
closed suction or discharge valve. The
pump will overheat, and may rupture or
explode, causing personal injury or
death.
Open all valves in the suction and discharge lines,
and close all drain valves.
Consult the drive manufacturer's operating manu
al before attempting to start the drive.
In a suction lift, fill the pump housing with liquid to
seal clearances and to lubricate.
Checking Pump Rotation
Correct rotation of your pump is shown on the
pump serial plate or direction arrow plate.
In applications with a single direction of
flow and a single pump‐mounted pressure
relief valve, make certain that the drive unit
turns the pump in the correct direction of
rotation. Otherwise, the pump‐mounted
pressure relief valve will not function.
Follow the drive unit manufacturer's instructions,
jog the pump motor briefly, and check rotation.
Gorman‐Rupp rotary gear pumps are bi‐
directional; however, the pumps are
manufactured to rotate in one specific di
rection. If rotation is to be changed, the
pressure relief valve must be re‐installed
with the cap pointing toward the suction
port.
If a 3‐phase motor is being used and rotation is in
correct, have a qualified electrician interchange
any two of the 3‐phase wires to change the direc
tion of rotation. If a 1‐phase motor is being used
and rotation is incorrect, consult the motor man
ufacturer's literature.
STARTING
Start the drive unit as indicated in the manufactur
er's instructions and observe the suction and dis

GMC SERIESOM-04384
OPERATIONPAGE C-2
charge gauges. If the pump does not deliver liquid
within one minute, stop the drive unit. Do not oper
ate the pump more than one minute without liquid
in it; dry operation will damage or destroy the
pump.
Although this pump is self‐priming, never
operate it dry. Dry operation could cause
galling, seizing, damage to the seal or ex
cessive wear of rotating parts.
Review the previous steps outlined in PRE‐OP
ERATION and review TROUBLESHOOTING,
Section D. If everything appears normal, add liquid
to the pump housing to assist priming and start the
driver again.
If the pump does not deliver liquid within two min
utes, stop the pump; it may be necessary to vent
the discharge line until liquid begins to flow.
If the pump still does not deliver after consulting
TROUBLESHOOTING and venting the discharge
line, contact your local Gorman‐Rupp Rotary Gear
Distributor or the factory.
OPERATION
NOTE
If the pump malfunctions or does not meet operat
ing specifications, refer to TROUBLESHOOTING
- Section D.
A change in operating noise when liquid first enters
the pump is normal. After the pump is fully opera
tional, monitor it for any unusual noises or vibra
tion; if either occurs, shut the pump down immedi
ately.
Liquid Temperature
Do not install the pump in a service with higher liq
uid temperatures than what it was designed. Intro
ducing hot liquid into a cold pump will expand
parts unevenly, causing excessive wear, pump fail
ure, and operation may be affected. This thermal
shock can be reduced by gradually heating the liq
uid being introduced into the pump. If it is not pos
sible to heat the liquid, use heat tape and/or insula
tion to heat the pump.
High temperature bushings as well as optional
jackets which may be used to heat or cool the
pump are available options for many models.
Overheating
Overheating can occur if the pump is operated with
valves in the suction or discharge lines closed. Op
erating against closed valves could bring the liquid
to a boil, build pressure, and cause the pump to
rupture or explode. If overheating occurs, stop the
pump and allow it to completely cool before servic
ing.
Do not remove plates, covers, gauges,
pipe plugs or fittings from an overheated
pump. Vapor pressure within the pump
can cause parts being disengaged to be
ejected with great force. Allow the pump to
completely cool before cooling.
Checking Gauges
Monitor vacuum and pressure gauge readings to
ensure that the pump is operating within normal
range and delivering full flow.
Strainer Check
If a strainer has been installed in the suction line,
monitor vacuum gauge readings to detect block
age. Check the strainer if flow rate begins to drop.
Never introduce air or steam pressure
into the pump housing to remove a
blockage. This could result in personal
injury or damage to the equipment. If
backflushing is absolutely necessary,
limit liquid pressure input to 50% of the
maximum permissible operating pres
sure shown in the pump performance
data.

OM-04384GMC SERIES
PAGE C-3OPERATION
Leakage
No leakage should be visible at pump mating sur
faces or at pump connections or fittings. Keep all
line connections and fittings tight to maintain maxi
mum efficiency.
If your pump is equipped with a packing seal, the
packing is lubricated by the liquid being pumped.
Some leakage around the packing seal is normal.
Packing pumps must leak slightly to cool and lu
bricate the shaft and to allow the shaft to turn freely.
Wait until the pump has run long enough to reach
its normal operating temperature to adjust the
gland nuts. Adjust the nuts only tight enough to re
duce excessive leakage.
PRESSURE RELIEF VALVE
ADJUSTMENT
Some pumps are not provided with a pressure re
lief valve. A pressure relief valve must be installed
on the pump or in the discharge piping to ensure
safe operation. Otherwise, the pump may be dam
aged and personnel injured.
If operating at high temperatures, allow the
pump to completely cool before attempt
ing any adjustments.
Cracking Pressure
Cracking pressure is the pressure at which the
pressure relief valve first begins to open and by
pass fluid. The nominal cracking pressure of the re
lief valve provided with this pump is set at the facto
ry and is indicated on the tag attached to the relief
valve.
If the nominal cracking pressure set at the factory
must be changed, see Table E‐2 and instructions in
Section E ‐ MAINTENANCE AND REPAIR.
Complete By‐pass Pressure
Complete by‐pass pressure is the maximum pres
sure the pump will see when all the pumped fluid is
being by‐passed through the pressure relief valve.
This pressure will vary depending on the cracking
pressure setting, liquid viscosity, and pump speed
(pump capacity).
To determine the complete by‐pass pressure, refer
to the pump performance chart or consult the fac
tory.
Do not remove the adjusting screw jam
nut; with the jam nut removed the relief
valve spring(s) can be compressed too
far for the valve to open. If the valve
does not open, excessive pressure can
develop, causing damage to the pump
and possible injury to personnel.
STOPPING
If the pump will be out of service for an extended
length of time, particularly when handling non‐lu
bricating liquids, drain the system and flush the
pump and piping with an oil‐based preservative to
protect close‐tolerance pump parts.
When handling liquids that solidify when at rest
(tar, glue, etc.), flush the pump and piping with an
approved solvent compatible with the pump com
ponents and the liquids being pumped.

GMC SERIES OM-04384
PAGE D-1TROUBLESHOOTING
TROUBLESHOOTING - SECTION D
Review all SAFETY information in Section A.
Before attempting to open or service the
pump:
1. Familiarize yourself with this manual.
2. Allow the pump to completely cool if
overheated.
3. Check the temperature before open
ing any covers, plates, or plugs.
4. Close the suction and discharge
valves.
5. Drain the pump.
TROUBLESHOOTING WITH GAUGES
Most pump or system malfunctions can be detected by installing vacuum suction and discharge pressure
gauges. Read the gauges and refer to the following information for interpretation of the gauge readings. For
additional troubleshooting procedures, see the TROUBLESHOOTING CHART.
Vacuum Gauges
HIGH READING
Suction valve closed, suction line blocked,
foot valve jammed, strainer blocked.
Liquid too viscous.
Lift too high.
Suction line undersized.
LOW READING
Air leak in suction line.
End of suction line not submerged.
Pump parts worn or defective.
Pump needs priming.
ERRATIC READING
Liquid overheated, vaporizing.
Liquid entering intermittently, suction air leak,
end of suction line not submerged.
Vibration from cavitation, misalignment, dam‐
aged parts.
Pressure Gauges
HIGH READING
Liquid too viscous.
Discharge line undersized or too long.
Discharge valve partially closed.
Strainer blocked.
Relief valve pressure set too high.
Thermal changes in liquid.
LOW READING
Relief valve pressure set too low.
Internal valve not seating properly.
Pump bypass partially open.
End clearance too great.
Pump parts worn or defective.
ERRATIC READING
Cavitation.
Liquid entering intermittently, suction air leak,
End of suction line not submerged.
Drive misalignment causing vibration.

GMC SERIESOM-04384
PAGE D-2 TROUBLESHOOTING
TROUBLESHOOTING CHART
Shaft seal leaking; gaskets, O‐rings
worn.
TROUBLE POSSIBLE CAUSE PROBABLE REMEDY
PUMP DOES
NOT DELIVER
RATED DIS
CHARGE OR
CAPACITY
PUMP FAILS
TO PRIME OR
LOSES PRIME
Air leak in suction line; end of suction
line not submerged; foot valve blocked
or jammed; insufficient liquid in sump or
tank.
Check and correct as required.
Shaft seal leaking; gaskets, O‐rings
worn.
Check vacuum gauge; disassemble
pump and replace faulty parts.
Leaking relief valve. Disassemble and repair.
Suction lift too high. See INSTALLATION, SECTION B and
check piping.
Suction strainer clogged. Check strainer.
Pump rotation incorrect. See OPERATION, SECTION C and
check rotation.
Pump speed too slow. Check driver speed.
Check and correct as required.
Readjust.
Suction or discharge lines blocked;
suction or discharge valves closed.
Check strainer, valves and piping.
Air leak in suction line; end of suction
line not submerged; foot valve blocked
or jammed; insufficient liquid in sump or
tank.
Check vacuum gauge; disassemble
pump and replace faulty parts.
Relief valve pressure set too low.
Housing dry. Add liquid to housing, see OPERATION,
SECTION C.
Rotating parts worn or damaged; im
proper end clearance.
Replace defective parts; see SETTING
END CLEARANCE in Maintenance And
Repair, Section E.
Pump speed too slow. Check driver speed; check belts/coup
lings.
PUMP RE
QUIRES
TOO MUCH
POWER Pump speed too high. Reduce driver output.
Internal parts worn. Disassemble pump and inspect.
Discharge line undersized and/or too
long.
Increase size, decrease length.
Pump “starving” or liquid vapor
izing in suction line.
Increase suction pipe size or reduce
length; position pump below liquid level.
Pump “starving” or liquid vaporizing
in suction line.
Increase suction pipe size or reduce
length; position pump below liquid level.
Insufficient end clearances. Readjust clearance; see SETTING END
CLEARANCE in Maintenance and Re
pair, Section E.

GMC SERIES OM-04384
PAGE D-3TROUBLESHOOTING
TROUBLESHOOTING CHART (Cont.)
TROUBLE POSSIBLE CAUSE PROBABLE REMEDY
Power source undersized. Check power requirements for applica
tion; resize as required.
EXCESSIVE
NOISE OR
VIBRATION Pumping entrained air. Check liquid level.
Pump operating outside designed
operating range.
Check discharge head and flow; adjust as
required to meet performance specifica
tions.
PUMP RE
QUIRES
TOO MUCH
POWER
(Cont.)
Pump and/or drive mounting not
secure; drive misaligned.
Tighten mounting hardware; realign
drive.
Rotating parts worn or damaged; im
proper end clearance.
Replace defective parts; check end
clearance.
Liquid in pump solidified. Clear or heat.
Relief valve chatter. Increase pressure setting.
Lubrication required. Add lubricant, as needed.
Corrosive liquid. Check local distributor or factory for
parts compatibility with liquid; check liq
uid for contamination.
EXCESSIVE
WEAR
Exceeding operating limits. Check performance data in Pump Speci
fications Bulletin.
Insufficient end clearance. See SETTING END CLEARANCE in
Maintenance And Repair, Section E.
Pump running dry. Add liquid to prime (See Operation, Sec
tion C); check liquid flow.
Pump and/or drive mounting not se
cure; drive misaligned; piping incor
rectly installed.
Tighten mounting hardware; realign
drive; check piping.
Insufficient lubrication. Add lubrication and maintain at proper lev
el.
Pump “starving” or liquid vapor
izing in suction line.
Increase suction pipe size or reduce
length; position pump below liquid level.
Pump and/or piping not secure; drive
misaligned.
Anchor base or piping, realign drive.
Insufficient internal clearances. Consult factory.
Abrasive liquid. Consult factory.

GMC SERIESOM-04384
PAGE D-4 TROUBLESHOOTING
PREVENTIVE MAINTENANCE
Since pump applications are seldom identical, and
pump wear is directly affected by such things as
the abrasive qualities, pressure and temperature
of the liquid being pumped, this section is intended
only to provide general recommendations and
practices for preventive maintenance. Regardless
of the application however, following a routine pre
ventive maintenance schedule will help assure
trouble‐free performance and long life from your
Gorman‐Rupp rotary gear pump. For specific
questions concerning your application, contact
your Gorman‐Rupp distributor or the Gorman‐
Rupp Company.
Record keeping is an essential component of a
good preventive maintenance program. The ap
pearance of wearing parts should be documented
at each inspection for later comparison. Also, if re
cords indicate that a certain part (such as the seal)
fails at the same duty cycle, this part can be
checked and replaced before failure occurs.
Because of the tight tolerances within your rotary
gear pump, wear between rotating parts is normal
and expected. For new applications, a first inspec
tion at 250 hours will give insight into the wear rate
for your particular application. Subsequent inspec
tions should be performed at regular intervals of
2000 hours. Critical applications should be in
spected more frequently.
Check the thrust washer (medium duty models),
idler bushing, idler pin, idler assembly, shaft bush
ing and rotor/shaft assembly at each inspection.
Wear patterns should be uniform, without evi
dence of deep or irregular grooves.
For packing pumps, periodic adjustment of the
packing is required to keep leakage to a minimum
(see the adjustment procedure described under
Leakage in Operation, Section C). Do not over
tighten. Replace the packing if leakage cannot be
reduced by a slight adjustment.
If the pump is equipped with a backhead bearing
(heavy duty models), inspect for free rotation of the
shaft and rotor, and excessive endplay or radial
movement of the shaft, which could indicate bear
ing wear. Remove the rotor adjusting sleeve as
sembly and inspect the bearing for damaged
seals. Replacing the bearing at the first indication
of a problem can extend the life of the pump and
save considerable expense later to replace major
components that can be damaged if the bearing is
allowed to fail.
After extended service, adjustment of the clear
ance between the rotor and the head will normally
improve performance (see the adjustment proce
dure in Maintenance And Repair, Section E).
If the pump is to be removed from service for repair,
be sure to protect the internal components from
rusting while the pump is disassembled and after
reassembly if not immediately placed back into
service.

GMC SERIES OM-04384
PAGE E-1MAINTENANCE AND REPAIR
MAINTENANCE AND REPAIR - SECTION E
MAINTENANCE AND REPAIR OF THE WEARING PARTS OF THE PUMP WILL
MAINTAIN PEAK OPERATING PERFORMANCE.
Pump Model
Your pump model number and serial number are shown on the Parts List, furnished as a
separate document with this manual.
Below the pump model number on the Parts List, is a grouping of several alpha‐numeric
codes. This code identifies the optional features of the pump. Be sure to include this
grouping, along with the model number and serial number, when ordering parts.
The sectional views cover disassembly and reassembly for the pump models shown be
low. Refer to the Parts List for your specific pump model.
The Following Pumps Are Covered By This Manual.
GMC SERIES
PUMPS
3-B

OM-04384 GMC SERIES
PAGE E-2 MAINTENANCE AND REPAIR
Shown: Standard Model With 180Ports and Housing‐Mounted Relief Valve. Also Available With 90Ports, BackHead
Adaptor, and Head‐Mounted Relief Valve. A Coverplate Kit Replaces Either Relief Valve When Not Used.
NOTE: Refer to Seal Appendix, Section F for details of the seal assembly and related components.
46166-067
Figure E-1. Typical GMC Pump Models