Welch 8905 User manual

OWNER’S MANUAL
FOR
DIRECTORR® DIRECT-DRIVE VACUUM PUMP
MODELS:
8905
8907
8912
8917
8920
8925
Gardner Denver Welch Vacuum Technology, Inc.
5621 W. Howard Street
Niles, IL 60714
Phone: [phone]
Fax: [phone] (Technical Support)
E-Mail: [email protected] Part No. 67-1483R2.5
Web-Page: www.welchvacuum.com Printed in USA
For outside of U.S. and Canada, contact your local
Gardner Denver sales office, see back page
WARNING
Do not block the exhaust port. Pressure will build up with the
potential of oil case bursting with possible injury to personnel.
WARNING
Pumps being run continuously above 1 torr should use an
exhaust oil recycler.
WARNING
Pumps not recommended for filtration, aspiration or drying
electrophoresis gels.

INSTRUCTION
WARNING AND CAUTION
PLEASE READ BEFORE OPERATION
While reading your manual, please pay close attention to areas labeled:
WARNING AND CAUTION.
The description of each is found below.
These units conrm to the SI International system of units of measurement.
The following symbols (with recommendation of IEC1010 ) of warning will be found on the pump.
Caution - refer to accompanying documents
Caution - risk of electrical shock
Caution - hot surface
2
WARNING
Warnings are given where failure to observe instruction could
result in injury or death to people.
WARNING
Motor includes a self resetting thermal cutout and the pump could
restart without actuation under fault condition.
CAUTION
Cautions are found where failure to observe the
instruction could result in damage to the equipment,
associated equipment and process.

TABLE OF CONTENTS
SECTION PAGE
Section 01 - Installation 05
1.01 Unpacking 05
1.02 Pump Mounting 05
1.03 Pump Location / Environmental Conditions 05
1.04 Exhaust Provisions 05
1.05 Electric Power 06
1.06 Vacuum Connections 07
1.07 Vacuum Gauges 07
1.08 Vacuum Pump Oil 07
Section 02 - Pump Features & Principles of Operation 08
2.01 General Description 08
2.02 Principles of Vacuum Pump Operation 09
2.03 Effects of Continued Pressure Reduction 09
2.04 Ultimate Pressure 09
2.05 Pump Mechanism Description 09
2.06 Intake Anti-Suckback Protection 10
2.07 Pump Lubrication 10
2.08 Exhaust Filter 10
2.09 Gas Ballast Valve 10
2.10 UNIBARBTM Intake Fitting 11
Section 03 - Specications 12
3.01 Specication Chart 12
Section 04 - Motor Power Specications / Features 14
4.01 Motor Specications Chart 14
4.02 Changing the voltage setting; 8907, 8912 & 8917 “A” Models 15
4.03 Changing the voltage setting; 8907, 8912 & 8917 “C” Models 15
4.04 Changing the voltage setting; 8905, 8920 & 8925 “A” Models 16
(Includes instructions to attach solenoid valve)
4.05 Other Electrical Congurations 16
4.06 Explosion Proof Pumps 16
Section 05 - Operation 17
5.01 Starting Procedure 17
5.02 High Pressure Operation 17
5.03 Shutdown Procedures 17
3

4
TABLE OF CONTENTS
SECTION PAGE
Section 06 - Maintenance 18
6.01 Vacuum Problems 18
6.02 Oil Change 19
6.03 Developing a Maintenance Schedule 19
6.04 Lip Seal / Gasket Change 20
Section 07 - Trouble Shooting 24
7.01 Leak Detection Problems 24
7.02 Trouble Shooting Guide 25
Section 08 - Specications 26
8.01 Shaft Seal Replacement 26
8.02 Minor Repair Kits 26
8.03 Major Factory Repair 26
Section 09 - Accessories 27
9.01 Pump Oil 27
9.02 Exhaust Filter 27
Section 10 - Drawings and Speed Curve 28
10.10 Speed Curve 28
10.20 Dimensional Drawing 29
10.30 Pump Exploded Views and Parts List 30
10.40 Module Exploded Views and Parts List 36
10.50 Oil Case Exploded View and Parts List 39
Section 11 - Warranty 40
Section 12 - MSDS Sheet for 8995P 41

5
Section 1: INSTALLATION
1.01 Unpacking
Carefully remove the pump from the shipping carton. Keep all paperwork and inspection tags for future
reference. If shipping damage has occurred, a claim must be led with the carrier immediately; keep the
shipping container for inspection by the carrier.
1.02 Pump Mounting
Rubber bumpers are supplied with the pump base. They isolate noise and eliminate creeping. For more
rigid mounting requirements the pump base can be bolted directly to a surface by removing the bumpers
from the base and using the mounting holes and slots featured on the base.
1.03 Pump Location / Environmental Conditions
The pump should be located in a clean and well-ventilated area and adequate space should be provided
wherever possible for routine maintenance such as oil changes. For best performance, the pump should
be located as closely as possible to its system. Determining factors for pump location should include
length and size of connections, the number of bends, and the type of exhaust connections.
1.04 Exhaust Provisions
Exhaust connections will be determined by the type of system to be exhausted and the desired
cleanliness of the air surrounding the pump. Under normal pumping conditions the optional exhaust
lter will be adequate. Refer to Section 9, Accessories for available exhaust lters. Where extreme
exhaust conditions are encountered, it is best to pipe the exhaust out of the building. Always use thick
walled rubber vacuum hose, wire reinforced PVC tubing or metal pipe for exhaust lines to avoid the
possibility of the line becoming crimped or collapsing resulting in dangerous exhaust line blockage.
The exhaust connection is a 1”-20 threaded port for all Models except 8905 which is 3/4”-20. The port
is located on top of the oil reservoir. See section 9.02 Exhaust Filters to nd the correct lter for each
pump. If a hose nipple is preferred for the exhaust port, use part number 1393K for models 8907, 8912
and 8917.
Call Welch customer support [phone], ext. 1, prior to start-up if you have any questions.
WARNING
Never block or impede air flow from the exhaust port. High
pressure can build up within the oil reservoir if the exhaust port
is blocked. Check frequently, especially if exhaust is piped
out of the building.

6
1.05 Electric Power
For Model 8905
Compare the pump motor rating, printed on a label on the side of the motor and on the serial number tag,
to the power source, to be sure they agree in voltage, phase, and frequency. Pump installation must
comply with local electrical codes which dictate appropriate protection devices such as fuses or circuit
breakers. Know the location of the circuit breaker protecting the electrical outlet for the pump.
For Models 8907, 8912 & 8917
Compare the pump motor rating, printed on a label on the side of the motor and on the serial number tag,
to the power source, to be sure they agree in voltage, phase, and frequency. Pump installation must
comply with local electrical codes which dictate appropriate protection devices such as fuses or circuit
breakers. Know the location of the circuit breaker protecting the electrical outlet for the pump.
Only the Models 8907C, 8912C and 8917C have “global motors” that operate over a wide range of
voltages (100-120V, 200-30V). They also operate at frequencies of 50Hz and 60 Hz.
Power is single phase.
For Models 8920 & 8925
Compare the pump motor rating, printed on a label on the side of the motor and on the serial number tag,
to the power source, to be sure they agree in voltage, phase, and frequency. Pump installation must
comply with local electrical codes which dictate appropriate protection devices such as fuses or circuit
breakers. Know the location of the circuit breaker protecting the electrical outlet for the pump.
CAUTION
Make certain the power settings on the pump match your power
source before attempting to operate the pump.
(Additional information can be found in section 4: Motor Power).

7
1.06 Vacuum Connections
The pump inlet is equipped with a UNIBARBTM 7/16” and 13/16” hose tting. The inlet is located
next to the pump handle. It contains a screen to collect any debris from getting into the pump. An
extensive line of vacuum pump ISO ttings, hoses, traps, etc. is available from Welch to meet the
requirements of most vacuum systems. For the best vacuum, use a hose clamp in conjunction with a
vacuum hose to hose nipple connections. Welch offers a number of different types of vacuum tubing
and connectors.
See Section 9 - Accessories or call Welch customer support [phone], Extension 1.
The choice of connections and ttings can have a very marked effect on the pumping speed at the
vacuum chamber. Any connection placed between the pump and the chamber creates an impedance to
the ow of gas. This is particularly true at low pressures in the millitorr range where the gas ow is
substantially molecular in character. The gas ow is then dependent upon the kinetic activity of the
molecules to bring it to the pump intake. This impedance is described by the term “conductance”.
The conductance of a tube is proportional to the cube of its diameter and inversely proportional to its
length. Therefore, connecting lines should be as large in diameter and as short in length as practical.
For best results the diameter of the connecting tube should be at least as large as the diameter of the
pump intake. To avoid a large reduction in pumping speed at the vacuum chamber, the conductance of
the line must be considerably greater than the speed of the pump. Sharp bends in vacuum lines also
contribute to conductance. To avoid reductions in pumping speed, minimize the number of 90º angles
in the vacuum system.
1.07 Vacuum Gauges
The type of vacuum gauge to be used in a system is determined largely by the pressure range to be
measured. A thermocouple or pirani gauge is recommended for measuring pressures in the range
produced by these pumps. See Website or call for additional information.
1.08 Vacuum Pump Oil
Filling with Fresh Oil
Be sure the pump is lled with oil to the level indicated on the oil ll window. When additional oil is
required, use only DIRECTORR® Gold Vacuum Oil , pump performance is not guaranteed with other
brands of oil. Do not overll the pump, and be sure to replace the oil ll plug.
Remove the oil ll plug located on the top of the oil case and add the oil supplied in a bottle packaged
with each pump.
The ll plug has a raised middle section and a center slot for easy turning either by hand or with a
screwdriver. After the pump has been running for at least 15 minutes, check the oil level again. The oil
level should be maintained at the “full” mark on the oil level window while the pump is operating. Do
not overll, excess oil tends to be splashed out the pump exhaust.
Guidelines for the frequency of oil changes and the oil changing procedure can be found in
Section 6-2: Oil Change
WARNING
The vacuum pump is shipped witout oil inside to prevent possible
spillage during shipment. Oil must be added prior to use.
WARNING
Use only DIRECTORR® Premium or Gold Vacuum Pump Oil.

8
Section 2: PUMP FEATURES AND PRINCIPLES OF OPERATION
2.01 General Description
All of the Welch Vacuum Pumps are two-stage, rotary-vane, oil sealed vacuum pumps.
These Vacuum Pumps offer a number of features that improve performance, or protect the pump or
vacuum system under specic operating conditions.
2.02 Principles of Vacuum Pump Operation
The main purpose of a vacuum pump is to reduce the pressure in a vessel or a closed system. The
degree of pressure reduction is dependent upon the requirements of the application and the type of
vacuum pump employed. Rotary vane, oil-sealed vacuum pump operation is described in this section.
Pressure reduction in a closed system is accomplished by repeatedly removing a portion of the
original volume of gas contained in the system. Removal is performed by the action of the rotating
elements of the pump which cause a given space to be successfully enlarged and diminished. Figure 2.1
illustrates a section through a typical stage of rotary-vane pump. Note that this gure is not intended to
illustrate exactly the internal components of the pumps; its purpose is to illustrate the general operating
principles of vacuum pumps.
The rotary action of the pump creates a hollow space of chamber (1) which expands as the pump rotates.
As the chamber expands, the pressure in the chamber decreases. As a result, gas is drawn into the
chamber due to the difference in pressure between the chamber and the inlet (4) to the chamber. (The
inlet is the only place where gas can ow into the chamber.) Once the vane (3) moves past the inlet (4),
it seals the inlet against the chamber (1) and the gas becomes trapped between the vanes (2 and 3). The
chamber (1) formed by the enclosed space between the vanes then begins to decrease in volume as the
rotor revolves, compressing the gas. The pressure of the compressed gas becomes greater than
atmospheric pressure. When the vane (2) moves past the exhaust port (5) the compressed gas in the
chamber is forced out through the exhaust port.
Figure 2.1
Typical Rotary Vane
Pump, Schematic Diagram
This expansion/compression cycle constitutes one complete cycle of the pump operation. This cycle is
repeated as the vane (2) passes the intake port and seals it against the atmosphere. Therefore, two pump
cycles are performed during each revolution of the pump rotor.

9
2.03 Effects of Continued Pressure Reduction
The quantity of gas in the vessel (6) is reduced with each evacuation cycle. The gas remaining in the
vessel expands to ll the vessel and consequently with each cycle the pressure in the vessel is reduced.
This is a manifestation of Boyle’s Law which states that, for a constant temperature, the volume of a
body of gas is inversely proportional to its pressure; i.e., if the volume is enlarged the pressure must be
reduced.
As the amount of gas in the vessel is steadily diminished, its pressure is correspondingly reduced. The
action of the pump must therefore compress a successively smaller quantity of gas with each cycle to
something greater than atmospheric pressure in order to expel it from the pump.
At the beginning of an evacuation sequence, the compression ratio is very small. In the rst cycle of
operation the pump draws in a volume of gas at atmospheric pressure and expels it at approximately
atmospheric pressure. In contrast, near its ultimate pressure, a pump draws in gas at (for example) 30
millitorr and must compress it to more than 760,000 millitorr (atmospheric pressure) in order to expel it
from the pump. Since the exhaust valve is generally spring loaded to provide a good seal, the pressure
required to open it is somewhat greater than atmospheric pressure. Therefore, at an ultimate pressure
of 1.3 x 10-4 mbar 0.1 millitorr, (1 x 10-4 Torr) the compression ratio performed by the pump is greater
than 1,000,000 to 1.
2.04 Ultimate Pressure
As described previously, a quantity of gas is removed from the system with each cycle of the pump.
Therefore, the pressure of the gas remaining in the system is reduced with each pump cycle. Since the
pump can remove only a small portion of the gas with each pump cycle, it is obvious that this method of
evacuation can never completely remove all the gas in the vessel. In addition to this, all the components
of the system contain minute sources of gas leakage which are impossible to seal completely against
atmospheric pressure. Outgassing of materials within the system provide additional sources of gas.
As a result, after prolonged pumping, a state of equilibrium is reached in which the gas introduced from
all the leakage sources is balanced by the ability of the pump to remove gas from the system. This state
of equilibrium is referred to as the ultimate pressure or blankoff pressure of the pump and its system.
No matter how much additional pumping time is provided, no further reduction in system pressure will
be accomplished once ultimate pressure is attained.
2.05 Pump Mechanism Description
This vacuum pump incorporates two in-line rotary-vane stages with interconnecting ports. When in
operation, the intake stage is at lower pressure and the exhaust stage is at higher pressure relative to each
other. Each stage contains a rotor assembly consisting of a rotor with two vanes and a stator. The two
rotors are combined on one shaft, and the two stators are combined in a common housing. The pump
shaft turns the rotors, causing the vanes in each section to sweep the surface of their stators. The vanes
are pressed against the stators by centrifugal force.
Each stage has an exhaust valve. Gas expelled from the rst stage exhaust passes through an interstage
port to the intake of the second stage. The second stage compresses the gas further, then expels it from
the second stage exhaust valve to the atmosphere.
An adjustable gas ballast valve is located in the pump’s exhaust stage. The purpose of the gas ballast is
to reduce or eliminate vapor condensation in the pump. The function of the gas ballast valve is
described later in this section.
The pump is mounted inside an oil case which is a reservoir for the oil that lubricates the pump. The
electric motor shaft drives the pump shaft via a coupling. There is a coupling body on the end of each
shaft; a coupling spider between the two coupling bodies transfers the power from the motor shaft to the
pump shaft.

10
2.06 Intake Antisuckback Protection
When power to the pump is turned off, this device closes automatically, maintaining vacuum in the
system being evacuated, and vents the inside of the pump to atmospheric pressure.
2.07 Pump Lubrication
To ensure efcient operation and proper maintenance, and to minimize noise and oil vapors, it is
important to use the correct type and quantity of oil. DIRECTORR® Gold Vacuum Oil has been
especially developed to have the proper viscosity, low vapor pressure, and chemical stability needed to
produce peak pumping efciency. The ultimate vacuum guarantee on Welch pumps applies only when
this oil is used. Therefore, DIRECTORR® Gold Vacuum Oil is the only oil recommended for use with
these pumps. Each pump is supplied with sufcient oil for lling. Additional oil is available.
See Section 9: Accessories.
2.08 Exhaust Filter
Any oil-sealed vacuum pump tends to discharge oil mist from its exhaust port when the pump operates
under high-ow conditions, such as when the pump’s intake is at or near atmospheric pressure.
Typically, oil mist in the form of a white puff of “smoke” can be seen from the exhaust port when no
lter is used. Once the vacuum level and the corresponding air ow through the pump are reduced, very
little, if any, oil mist will be emitted.
An exhaust lter is recommended for any vacuum pump installation where the pump operates at high
intake pressures for a prolonged period of time. Oil droplets entrained in the pump’s exhaust are
removed by the exhaust lter element. Use of an exhaust lter typically reduces or bafes pump noise
as well. Exhaust lters are sometimes referred to as Oil Mist Eliminators. See Section 9 - Accessories.
2.09 Gas Ballast Valve
The gas ballast valve can increase the pump’s water vapor tolerance. (The gas ballast valve is sometimes
referred to as a vented exhaust valve.) In many vacuum pump applications the gases being pumped
from a system are a combination of permanent gases and undesirable vapors such as water vapor. Under
some conditions, the vapors condense in the second stage of the pump and contaminate the oil. The gas
ballast valve reduces oil contamination by decreasing or eliminating vapor condensation.
Vapor condensation is most likely to take place when the gas compression ratio is high, i.e. when the
pump compresses a relatively large volume of gas to a small volume. Whether or not condensation takes
place is dependent upon several factors, including the proportion of permanent gases to vapors at the
pump intake. If the gases being pumped consist entirely of vapors, condensation will denitely occur
unless the gas ballast valve is opened. The gas ballast valve adds a small amount of air at atmospheric
pressure to the gas being compressed in the second stage. This reduces the compression required to
push the gas out past the exhaust valve (less reduction in volume is required), and therefore reduces or
eliminates condensation.
When the gas ballast valve is open, the pump has to work a little harder, resulting in a slight increase in
operating temperature. The increase in temperature is small, however, and is not harmful to the pump.
Also, the pump is slightly noisier, and the pump’s ultimate pressure is somewhat reduced. Therefore, the
gas ballast valve should be kept closed when it is not needed. Note that the gas ballast is not equally
effective on all diffrent types of chemical vapors, so it may not always eliminate condensation
completely.

11
2.10 UNIBARBTM Intake Fitting - Simplies Small Hose Connections
The Unibarb intake tting allows the user to be able to use either 7/16” or 13/16” ID hose to connect to
this system. However, the choice of hose size can have a very marked difference on pumping speed. It
is the best to have the largest connection I.D.(internal diameters) as possible. However, we recognize
many lab appliances use hose barbs accepting small I.D. hose.
The conductance of a tube is proportional to the cube of its diameter and inversely proportional to its
length. Therefore, connecting line should be as large in diameter and short in length as practical.
Included is a free hose clamp to hold the hose in place.

12
Section 3: PUMP SPECIFICATIONS
3.01 Specication Chart
* Partial measurement based upon the American Vacuum Society Test Procedure No. AVS 5.1-1963
using a trapped McLeod Gauge.
SPECIFICATION 8905 8920 8925
Free Air Displacement
CFM (L/min) @ 60Hz 1.8 (52) 7.7 (218) 11.3 (320)
(L/min) m3h @ 50Hz (43) 1.5 (182) 10.8 (266) 16.0
Normal Pumping Speed
CFM (L/min) @ 60Hz 1.5 (43) 7.4 (210) 10.0 (283)
(L/min) m3h @ 50Hz (36) 1.3 (175) 10.5 (236) 14.2
Guaranteed Ultimate Pressure* Torr 2 x 10-3 3 x 10-4 4 x 10-4
Water Vapor Tolerance (capacity), Torr 6 15 15
Water Vapor Tolerance (capacity), g/hr 30 180 180
Sound Level dBA 56 54 55
Motor/Pump Speed
RPM @ 60Hz 3450 1725 1725
RPM @ 50Hz 2875 1425 1425
Motor Voltage 50/60Hz Single Phase
Current 115V (230V) @ 60Hz 3.8A (1.9A) 6.8A (3.4A) 10.0A (5.0A)
Current 230V @ 50Hz 1.2A 3.4A 5.0A
Motor Horsepower 1/4 1/2 3/4
Oil Capacity , quarts (liters) 0.42 (0.4) 1.3 (1.2) 1.2 (1.1)
Unibarb for Unibarb for Unibarb for
3/16" and 7/16" 9/16" and 13/16" 9/16" and 13/16"
Intake Connection I.D. Hose, I.D. Hose, I.D. Hose,
Threaded for Threaded for Threaded for
3/4"-20 1-1/8"-20 1-1/8"-20
Tubing needed, I.D.
in inches 3/16 or 7/16 9/16 or 13/16 9/16 or 13/16
in mm 5 or 11 14 or 20 14 or 20
Exhaust Connection 3/4"-20 Thread 1"-20 Thread 1"-20 Thread
Gas Ballast Connection 10-32 Thread 10-32 Thread 10-32 Thread
Pump Weight
lbs. 24.5 58.5 63
Kg. 11.1 26.6 31.3
Overall Dimensions
Length (inch / cm) 14.5 / 36.8 20.8 / 52.8 22.2 / 56.4
Width (inch / cm) 5.1/ 13 7.1 / 17.9 7.1 / 17.9
Height (inch / cm) 8.4 / 21.3 11.0 / 27.9 11.0 / 27.9
Shipping Weight
lbs. 26 71 77
Kg. 11.8 32.2 34.6
Shipping Carton Dimensions
Length (inch / cm) 21 / 53.3 29 / 73.7 29 / 73.7
Width (inch / cm) 6.5 / 16.5 10 / 25.4 10 / 25.4
Height (inch / cm) 11.2 / 28.6 14 / 35.6 14 / 35.6
Exhaust Filter (Optional) Cat. No. 1416B / 1417 1417P-10 / 1416C 1417P-10 / 1416C
Oil Type Cat. No. 8995P / 8995G 8995P / 8995G 8995P / 8995G

13
* Partial measurement based upon the American Vacuum Society Test Procedure No. AVS 5.1-1963
using a trapped McLeod Gauge.
SPECIFICATION 8907 8912 8917
Free Air Displacement
CFM (L/min) @ 60Hz 2.6 (70) 3.8 (108) 6.1 (173)
(L/min) m3h @ 50Hz (56) 3.68 (86) 5.37 (138) 8.63
Normal Pumping Speed
CFM (L/min) @ 60Hz 2.3 (64) 3.4 (96) 5.3 (150)
(L/min) m3h @ 50Hz (53) 3.2 (80) 4.78 (125) 7.51
Guaranteed Ultimate Pressure* Torr 1 x 10-4 1 x 10-4 1 x 10-4
Water Vapor Tolerance (capacity), Torr 19 12 12
Water Vapor Tolerance (capacity), g/hr - - -
Sound Level dBA 50 50 50
Motor/Pump Speed
RPM @ 60Hz 1725 1725 1725
RPM @ 50Hz 1425 1425 1425
Motor Voltage 50/60Hz Single Phase
Current 115V (230V) @ 60Hz 4.6A (2.3A) 4.6A (2.3A) 4.6A (2.3A)
Current 230V @ 50Hz 2.1A 2.1A 2.1A
Motor Horsepower 1/2 1/2 1/2
Oil Capacity , quarts (liters) 1.0 (0.95) 0.9 (0.86) 0.8 (0.76)
Unibarb for Unibarb for Unibarb for
7/16" and 13/16" 7/16" and 13/16" 7/16" and 13/16"
Intake Connection I.D. Hose, I.D. Hose, I.D. Hose,
Threaded for Threaded for Threaded for
1-1/8"-20 1-1/8"-20 1-1/8"-20
Tubing needed, I.D.
in inches 7/16 or 13/16 7/16 or 13/16 7/16 or 13/16
in mm 11 or 20 11 or 20 11 or 20
Exhaust Connection 1"-20 Thread 1"-20 Thread 1"-20 Thread
Gas Ballast Connection 10-32 Thread 10-32 Thread 10-32 Thread
Pump Weight
lbs. 40 41 48
Kg. 18 18 22
Overall Dimensions
Length (inch / cm) 18.8 / 47.7 18.8 / 47.7 18.8 / 47.7
Width (inch / cm) 6.5 / 16.6 6.5 / 16.6 6.5 / 16.6
Height (inch / cm) 9.6 / 24.4 9.6 / 24.4 9.6 / 24.4
Shipping Weight
lbs. 46 46 53
Kg. 21 21 24
Shipping Carton Dimensions
Length (inch / cm) 28.9 / 73.5 28.9 / 73.5 28.9 / 73.5
Width (inch / cm) 10.8 / 27.5 10.8 / 27.5 10.8 / 27.5
Height (inch / cm) 13.7 / 35.0 13.7 / 35.0 13.7 / 35.0
Exhaust Filter (Optional) Cat. No. 1416C / 1417P-7 1416C / 1417P-7 1416C / 1417P-7
Oil Type Cat. No. 8995P / 8995G 8995P / 8995G 8995P / 8995G

14
Section 4: MOTOR SPECIFICATIONS, POWER / FEATURES
4.01 Motor Specication Chart
Cat. No.
V
oltage Freq. Ph. H.P. Factory Wired fo
r
Special Feature
A
pproval
8905A 115 / 230 60 1 1/4 115V 60Hz Standard Model CSA
8905C-01 115 / 230 60 1 1/4 115V 60Hz 230V US Cord Plug CSA
8905C-02 230 50 1 1/4 230V 50Hz European "Schuko" Cord Plug CE
8905C-10 115 / 230 60 1 1/4 230V 60Hz European "Schuko" Cord Plug CSA
8907A 115 / 230 60 1 1/2 115V 60Hz Standard Model CSA
8907C-02 230 50 1 1/2 230V 50Hz European "Schuko" Cord Plug CE
8907C-05 100 50/60 1 1/2 100V For Japan with US Cord Plug -
8912A 115 / 230 60 1 1/2 115V 60Hz Standard Model CSA
8912C-02 230 50 1 1/2 230V 50Hz European "Schuko" Cord Plug CE
8912C-05 100 50/60 1 1/2 100V For Japan with US Cord Plug -
8917A 115 / 230 60 1 1/2 115V 60Hz Standard Model CSA
8917C-02 230 50 1 1/2 230V 50Hz European "Schuko" Cord Plug CE
8917C-05 100 50/60 1 1/2 100V For Japan with US Cord Plug -
8917W 115 60 1 1/2 115V 60Hz To be wired by qualified electrician -
8920A 115 / 208-230 50/60 1 3/4 115V 60Hz Standard Model CSA
8920C-01 115 / 208-230 50/60 1 3/4 230V 60Hz 230V US Cord Plug CSA
8920C-02 115 / 208-230 50/60 1 3/4 230V 50Hz European "Schuko" Cord Plug CE
8925A 115 / 208-230 50/60 1 3/4 115V 60Hz Standard Model CS
A
8925C-01 115 / 208-230 50/60 1 3/4 230V 60Hz 230V US Cord Plug CSA
8925C-02 115 / 208-230 50/60 1 3/4 230V 50Hz European "Schuko" Cord Plug CE
8925W 115 60 1 1/2 115V 60Hz To be wired by qualified electrician -

15
4.02 Changing the Voltage Setting on 8907, 8912 and 8917 “A”- Models only
The pumps are set for low voltage (LV) 115 volts 60 Hz.
They may also be set for high voltage (HV) 230 volts 60 Hz.
To change the voltage setting, see the wiring diagram below.
4.03 Changing the Voltage Setting on 8907, 8912 and 8917 “C”- Models with Global Motor Option
The voltage setting is permanently displayed in a small window on the pump motor electrical box.
The window is located next to the power cord connection and displays either
LV for 100-120V or HV for 200-230V.
To change VOLTAGE setting:
1. Disconnect the electrical power cord.
2. Open the motor electrical box by removing the
four screws and removing the cover.
3. Locate the voltage selection switch next
to the external electrical power cord connector.
4. Remove the voltage marker (61-6071).
The switch is very tightly installed.
To remove, place index and middle
nger along the top edge and pull backwards.
5. Change the voltage selection switch (61-1303)
to the opposite position.
6. Rotate the voltage marker, 180° and insert
into previous location. The voltage marker
is keyed to the switch setting so that it
can only display the correct setting. The
selected voltage setting can been seen through
the window in the electrical box.
7. Replace the electrical box cover
before reconnecting the power cord.
8. Attach solenoid valve leads. One lead of the
solenoid valve to orange motor wire, and one lead to yellow motor wire.
CAUTION
Make certain that the voltage setting (LV or HV) is in the
correct range for your power before plugging in.

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4.04 Changing the Voltage Setting on 8905, 8920 and 8925 “A”- Models only
The vacuum pump motor is factory wired to for 115 V for models which operate at 60 Hz, and 230 V
for models which operate at 50 Hz. The motor wiring can easily be changed for operation at a voltage
different than that set at the factory. Models can be rewired to operate at either the low (115 V) or high
(220 V) voltage. Follow the motor wiring schematic located below, or on the motor shield. A line cord
plug suitable for 115 V connection (blades parallel) or 220 V connection (blades coplanar) is furnished
which complies with United States electrical codes. When changing the factory wiring, or when using
outside of the United States, replace the line cord plug with one suitable for the voltage connection
which meets the voltage to which the motor now is wired to require to operate.
4.05 Other Electrical Congurations
Other electrical congurations of Welch pumps may be available. Check with Welch for 3-Phase,
Explosion Proof and other motor congurations.
4.06 Explosion Proof Pumps (Explosion Proof Pumps must be ordered special)
Due to the added safety features of an explosion proof pump, the pump’s electrical supply must be
connected onsite by a trained electrician. Since there are numerous scenarios for connection, the
manufacturer does not provide guidelines or advice in electrical hookups. Of course we will assist in
choosing the correct explosion proof pump, but for safety reasons, we resist the temptation to advise
what cannot be seen.

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Section 5: OPERATION
5.01 Starting Procedure
Before using the pump for the rst time, it is a good idea to spend a few minutes inspecting the pump
and its electrical and vacuum connections. Review Section 1: Installation as required.
Check the AC power outlet to be sure that it is the same voltage and phase as the pump motor.
Connect the power cord to the power outlet and recheck the oil level.
Close off the pump intake and the gas ballast valve, and run the pump at blankoff for a few minutes.
The gurgling noise should go away after a few minutes of running; it is caused by the high volume of
air that ows through the pump when the pump is rst turned on. If the gurgling noise does not stop,
check the oil level to see if it is low, and check the pump intake tting to be sure that it is tight. Once
proper pump operation has been veried, the pump intake can be opened to the vacuum system.
After running the pump for a few minutes, check the oil level again. If the level is too high or too low,
stop the pump and add or remove oil as needed. Stop the pump and vent it to the atmosphere before
adjusting the pump uid level.
Before starting the pump when connection to the vacuum system, check all vacuum connections.
5.02 High Pressure Operation
The Vacuum Pumps are designed to be most efcient when operated at or near their ultimate blankoff
pressure. When operated at elevated pressures for long periods of time, the pump will run hotter.
Additional cooling may be required for both the pump and the motor. At elevated ambient temperatures
under these conditions, the thermal protection switch may cut out. The oil may tend to thin out at these
temperatures, losing its ability to lubricate effectively.
During operation at these pressures, oil mist may be generated at the exhaust port. The mist has the
appearance of a small cloud of smoke. Use of an Exhaust Filter with coalescing element is required. An
exhaust lter with an oil drain back feature is highly recommended. See Section 9: Accessories.
5.03 Shutdown Procedures
A few simple precautions are necessary before performing a pump shutdown. If a gauge is connected to
the system, rst isolate the gauge, then turn off the power to the pump and open the system to the
atmosphere.
If the pump is disconnected from the system for any length of time, cover the pump intake with a rubber stop-
per or other suitable cover to protect the pump against contamination. An intake screen is furnished to prevent
loose particles from entering.
If the exhaust port is open, that should also be covered. If the pump oil is contaminated and the pump is go-
ing to be stored for a prolonged period, the oil should be changed before the pump is stored. Even if a pump
is stored for a long period with oil initially in good condition, check the oil when the pump is restarted, and
change the oil if necessary.
NOTE
The intake isolation valve will automatically close when power
to the pump is turned off. This will maintain vacuum in the system
(if the pump remains connected to the rest of the system).
NOTE
If operating this pump for prolonged periods of time at or
above 10 Torr,contact the Welch Vacuum Technical Service
Department for further information and precautions.

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Section 6: MAINTENANCE
6.01 Vacuum Problems
Inability to attain sufcient vacuum in a system is usually due to leakage, contamination, or unusual
outgassing. A system must be thoroughly clean and free from leaks to operate efciently. If the system
is found to be clean and leak-free, but vacuum problems still exist, the pump should be checked.
A simple way to test the pump is to measure its ultimate pressure capability. This can be done by
disconnecting the pump from the rest of the system and connecting a pressure gauge directly to the
pump intake. (Be sure to seal the pump intake from the atmosphere, and be sure the gas ballast valve
is closed.) The gauge can be any type that is suitable for the pressure levels expected. Run the pump
until the gauge indicates no further reduction in pressure, and compare the pressure reading to the
pump’s ultimate pressure rating.
If the pump meets its ultimate pressure specications only when disconnected from the rest of the
system, the fault must be elsewhere in the system. If the pump’s ultimate pressure is unusually high,
the pump may be badly contaminated, low on oil, or mechanically defective. However, if the pressure
is only slightly higher than the pump’s guaranteed pressure, an oil change may be all that is needed to
bring performance up to specications. Be sure to use only DIRECTORR® Premium or Gold Oil in
vacuum pumps; the ultimate pressure guarantee does not apply if other types of oil are used.
The most common cause of efciency loss in a vacuum pump is contamination of the oil, which is
usually caused by foreign particles and/or condensed vapors. The condensate emulsies with the oil,
and when the oil is recirculated, the condensate evaporates. The resulting vapor then reduces the
ultimate vacuum attainable in the system.
Some foreign particles and vapors form sludges with the oil. The presence of sludge in the oil impairs
its sealing and lubricating properties, and eventually could cause pump seizure. Therefore, periodic
oil changes are necessary to maintain efcient operation of the system. The interval at which oil
changes are required is different for each set of operating conditions; experience will help you determine
the proper interval for your system and process.

19
6.02 Oil Change
The best time to change the oil is when the pump is warm and the oil is less viscous.
Before attempting an oil change, the pump must be disconnected from the power outlet.
6.02.1 Changing the Oil on Models 8907, 8912 and 8917
To drain old oil, rotate the drain valve counter-clockwise until the handle will no longer turn. A 6-12 in.
length of 3/8” I.D. tubing can be tted on the oil drain nipple to direct the ow of oil neatly into a bottle
or other container. When the old oil has been removed, close the drain valve by rotating it clockwise
until the handle will no longer turn.
6.02.2 Changing the Oil on Models 8905, 8920 and 8925
Oil Removal: Drain the oil into a container by removing the plastic plug located below and to the left
of the oil sight glass. The pump may be tilted to remove residual oil out of the oil reservoir.
6.02.3 Oil Fill
Replace the oil drain plug, remove the plastic oil ll plug located on the top of the oil reservoir. Fill
the pump with vacuum oil until the level reaches the FULL mark of the label next to the oil sight glass.
Do not overll the pump. The excess oil tends to splash out of the exhaust. Replace the oil ll plug.
Check the oil level again after the pump warms up to its normal operating temperature. Add or remove
oil as needed. It is normal for the oil level to change upon initial start up.
6.02.4 Frequency of Oil Changes
The oil change interval is completely dependent upon the running conditions of temperature, operating
pressure, hours of daily operation, and upon the materials pumped. Clean, dry air at pressures below 50
mtorr are the most forgiving conditions. To determine your own oil change interval, visually monitor
the pump oil conditions at regular intervals. If you suspect harsh operating conditions, daily visual
checks are recommended. When the oil becomes cloudy, dark or includes particles of solids, it is time
to change the oil. Oil may be visually checked through the oil level window. However, a much better
check is to use the drain to draw out 20-50 ml into a small glass beaker and view the oil with a light
behind it. Clean oil can be returned to the pump through the oil ll port.
Be sure to use only DIRECTORR® Premium or Gold Oil.
The ultimate pressure guarantee applies only if those oils are used.
6.03 Developing a Maintenance Schedule
After studying many examples of pump failure, Welch has found the most common reason is poor
condition of the oil. This is why a regular maintenance schedule for the oil is critical to obtain the
longest service life out of your Vacuum Pump. Welch recommends that you examine the condition of
the oil on a daily basis in the early days of a new process or experiment. Look for discoloration of the
oil and whether the oil level is rising. The discoloration can indicate deterioration of the oil, and a rising
oil level can indicate condensation of vapors is occurring in the pump.
Once you have determined how long it takes for the oil to break down in your application, or become
contaminated, choose your oil change interval, so that the pump always operates with good quality,
uncontaminated oil.
WARNING
Hot oil can cause burns. Operating temperarue of the oil
is typically 140 degrees Fahrenheit or higher.
Avoid skin contact with oil.

20
6.04 Lip Seal / Gasket change
Changing the Lip Seal and Gasket for 8905
When the shaft seal in the mounting plate shows signs of excessive oil leakage, it should be replaced.
Before attempting replacement of the seal, the pump must be disconnected from the vacuum system and
from the power outlet. New lip seal (P/N 41-2988) and new gasket (P/N 61-2149B) or seal replacement
kit (Cat. No. 8905K-03) should be available before attempting repair.
1. DRAIN OIL by opening the drain plug. The pump may be tilted to remove residual oil out of
the oil case.
2. SEPARATE BASE from the pump by removing four socket head screws, 10-32x5/8.
3. SEPARATE THE PUMP FROM THE MOTOR ASSEMBLY by removing
four socket head screws #10-32x1 from the motor adapter plate. The isolator valve coil should
be slipped off by removing nut, name plate and large washer from valve projecting from the
inside of the mounting plate. Set aside the motor assembly with isolator coil placed next to it.
4. REMOVE OIL CASE from the pump by placing it on its mounting plate side and unscrew four
socket headscrews 10-32x3/4.
5. REMOVE COUPLING from the pump shaft by loosening the setscrew. Separate pump module
from then mounting plate by unscrewing three socket head screws #10-32x1/2 and three split
lock washers. Discard the gasket.
6. PUSH OUT LIP SEALS out of the wear plate with a blunt edge of a screwdriver blade.
Discard the lip seal. Older models will have lip seal installed in the mounting plate.
7. INSTALL NEW SHAFT SEAL with at side of the seal toward the motor. Use a little oil on the
lip seal outside periphery. The seal is located 0.09 in. from the coupling end inside the bore.
Seal assembly tool 61-2172A used to install and locate the lip seal.
8. PLACE THE PUMP MODULE on a table with shaft up. Slide shaft insertion tool 61-2170A
over the shaft end and place the new gasket over the modular assembly.
9. MOISTEN THE LIP SEAL, shaft and the tool with oil prior to the assembly. Slip the mounting
plate over the shaft of the modular pump.
10. ADJUST GASKET in proper angular location and then tighten gradually the 3 screws
#10-32x1/2 with lock washers.
11. ASSEMBLE COUPLING BODY to pump shaft all the way to the shaft shoulder and
tighten the setscrew.
12. ATTACH OIL CASE to the mounting plate using four socket head screws 10-32x3/4
with 4 lock washers. Tighten screws gradually.
13. Insert two dowel pins to the mounting plate and put the coupling spider in place.
14. ATTACH MOTOR ASSEMBLY to the mounting plate using four socket head screws #10-32x1
with lock washers. Watch for wires from the isolator valve coil to be placed in groove of motor
adapter plate during assembly. After carefully tting all parts together cross tighten the four
screws gradually.
15. ATTACH THE COIL TO ISOLATOR VALVE mechanism by rst slipping on the coil
shoulder and then the coil with name plate. Tighten the coil nut (name plate should turn freely).
16. ATTACH BASE to the mounting plate by means of four socket head screws 10-32x5/8 long.
17. FILL PUMP WITH OIL, DIRECTORR® Oil (Premium or Gold) and is ready to be inspected
for its performance.