BUSCH COBRA NC 1000 B User manual

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Instruction Manual
COBRA
Dry Screw Vacuum Pumps
NC 1000 B (water-cooled version)
0870551589/A0002_en / Original instructions / Modifications reserved 14/09/2021

Table of Contents
2 / 32 Instruction Manual COBRA NC 1000 B WCV_EN_en
Table of Contents
1 Safety ......................................................................................................................................4
2 Product Description...............................................................................................................5
2.1 Operating Principle.......................................................................................................... 6
2.2 Application....................................................................................................................... 6
2.3 Start Controls .................................................................................................................. 6
2.4 Standard Features .......................................................................................................... 6
2.4.1 Water Cooling....................................................................................................... 6
2.4.2 Resistance Thermometer ..................................................................................... 7
2.4.3 Level Switch ......................................................................................................... 7
2.4.4 Thermometer ........................................................................................................ 7
2.4.5 Sealing Systems................................................................................................... 7
2.5 Optional Accessories ...................................................................................................... 7
2.5.1 Gas Ballast Valve ................................................................................................. 7
2.5.2 Silencer ................................................................................................................ 7
2.5.3 Barrier Gas System .............................................................................................. 7
2.5.4 Mechanical Seals ................................................................................................. 7
3 Transport ................................................................................................................................8
4 Storage....................................................................................................................................8
5 Installation ..............................................................................................................................9
5.1 Installation Conditions ..................................................................................................... 9
5.2 Connecting Lines / Pipes ................................................................................................ 9
5.2.1 Suction Connection .............................................................................................. 10
5.2.2 Discharge Connection .......................................................................................... 10
5.2.3 Cooling Water Connection ................................................................................... 11
5.2.4 Barrier Gas System Connection (Optional) .......................................................... 12
5.3 Filling Oil ......................................................................................................................... 12
5.4 Filling Cooling Liquid ....................................................................................................... 14
5.5 Fitting the Coupling ......................................................................................................... 15
5.6 Electrical Connection ...................................................................................................... 15
5.6.1 Wiring Diagram Three-Phase Motor (Pump Drive) .............................................. 16
5.7 Electrical Connection of the Monitoring Devices............................................................. 17
5.7.1 Wiring Diagram Resistance Thermometer ........................................................... 17
5.7.2 Wiring Diagram Level Switch ............................................................................... 17
6 Commissioning ......................................................................................................................17
6.1 Conveying Condensable Vapours................................................................................... 19
7 Maintenance ...........................................................................................................................19
7.1 Maintenance Schedule.................................................................................................... 20
7.2 Oil Level Inspection......................................................................................................... 20
7.3 Cooling Liquid Level Inspection ...................................................................................... 21
7.4 Replacing the Gas Ballast Filter (Optional) ..................................................................... 21
7.5 Oil Change ...................................................................................................................... 21
7.6 Cooling Liquid Change.................................................................................................... 24
8 Overhaul..................................................................................................................................25
9 Decommissioning ..................................................................................................................26
9.1 Dismantling and Disposal................................................................................................ 26
10 Spare Parts .............................................................................................................................26
11 Troubleshooting.....................................................................................................................27

Table of Contents
Instruction Manual COBRA NC 1000 B WCV_EN_en 3
12 Technical Data........................................................................................................................29
13 Cooling Liquid........................................................................................................................29
14 Oil ............................................................................................................................................29
15 EU Declaration of Conformity...............................................................................................30

1 | Safety
4 / 32 Instruction Manual COBRA NC 1000 B WCV_EN_en
1 Safety
Prior to handling the machine, this instruction manual should be read and understood.
If anything needs to be clarified, please contact your Busch representative.
Read this manual carefully before use and keep for future reference.
This instruction manual remains valid as long as the customer does not change any-
thing on the product.
The machine is intended for industrial use. It must be handled only by technically
trained personnel.
Always wear appropriate personal protective equipment in accordance with the local
regulations.
The machine has been designed and manufactured according to state-of-the-art meth-
ods. Nevertheless, residual risks may remain. This instruction manual highlights po-
tential hazards where appropriate. Safety notes and warning messages are tagged
with one of the keywords DANGER, WARNING, CAUTION, NOTICE and NOTE as
follows:
DANGER
... indicates an imminent dangerous situation that will result in death or serious injuries
if not prevented.
WARNING
... indicates a potentially dangerous situation that could result in death or serious inju-
ries.
CAUTION
... indicates a potentially dangerous situation that could result in minor injuries.
NOTICE
... indicates a potentially dangerous situation that could result in damage to property.
NOTE
... indicates helpful tips and recommendations, as well as information for efficient and
trouble-free operation.

Product Description | 2
Instruction Manual COBRA NC 1000 B WCV_EN_en 5 / 32
2 Product Description
EB
IN
OUT
PMR
CLP
SI
OFP
SV
MP
OUT
CLFGB CLG
CDCLD
OSG
OSG
MP
MTB
NP
OFP
TSAODP
LS
TM
CWOPHECWI
ODPCLD
CD Condensate drain CLD Cooling liquid drain plug
CLF Cooling liquid fill plug CLG Cooling liquid sight glass
CLP Cooling liquid pump CWI Cooling water inlet
CWO Cooling water outlet EB Eye bolt
GB Gas ballast valve IN Suction connection
LS Level switch MP Magnetic plug
MTB Motor terminal box NP Nameplate
ODP Oil drain plug OFP Oil fill plug
OSG Oil sight glass OUT Discharge connection
PHE Plate heat exchanger PMR Plug for manual rotation of rotors
SI Silencer SV Safety valve
TM Thermometer TSA Resistance thermometer
NOTE
Technical term.
In this instruction manual, we consider that the term ‘machine’ refers to the ‘vacuum
pump’.

2 | Product Description
6 / 32 Instruction Manual COBRA NC 1000 B WCV_EN_en
NOTE
Illustrations
In this instruction manual the illustrations may differ from the machine appearance.
2.1 Operating Principle
The machine works on the one-stage, twin-screw pump principle.
Two screw rotors are rotating inside the cylinder. The pumped medium is trapped be-
tween the cylinder and screw chambers, compressed, and transported to the gas out-
let. During the compression process, the two screw rotors do not come into contact
with each other nor with the cylinder. There is no need for a lubrication or an operating
fluid in the compression chamber.
2.2 Application
The machine is intended for the suction of air and other dry, non-aggressive, non-toxic
and non-explosive gases.
Conveying of other media leads to an increased thermal and/or mechanical load on
the machine and is permissible only after a consultation with Busch.
The machine is intended for the placement in a non-potentially explosive environment.
The machine is capable of maintaining ultimate pressure, see Technical Data [►29].
The machine is suitable for continuous operation.
Permitted environmental conditions, see Technical Data [►29].
2.3 Start Controls
The machine comes without start controls. The control of the machine is to be provid-
ed in the course of installation.
The machine can be equipped with a soft-starter or a variable-frequency drive.
2.4 Standard Features
2.4.1 Water Cooling
The machine is cooled by a cooling liquid circuit in the cylinder cover and cylinder.
The cooling liquid pump (CLP) allows a recirculating flow in the cooling liquid cham-
ber.

Product Description | 2
Instruction Manual COBRA NC 1000 B WCV_EN_en 7 / 32
The cooling liquid is cooled by a plate heat exchanger (PHE) which must be connect-
ed to the water main.
2.4.2 Resistance Thermometer
The resistance thermometer monitors the cooling liquid temperature of the machine.
A trip signal must be set. The machine must be stopped when the cooling liquid tem-
perature reaches 70 °C.
2.4.3 Level Switch
The level switch monitors the cooling liquid level in the cylinder.
The machine must be stopped when the cooling liquid level is too low.
2.4.4 Thermometer
The thermometer allows a visual display of the cooling liquid temperature.
2.4.5 Sealing Systems
The machine is equipped with labyrinth seals on the motor side and suction side.
Other sealing systems are optionally available, see Mechanical Seals [►7].
Sealing systems prevent the process gas going to the bearings chambers.
Depending on the application, the sealing systems efficiency can be improved with a
barrier gas system, see Barrier Gas System [►7].
2.5 Optional Accessories
2.5.1 Gas Ballast Valve
The gas ballast valve mixes the process gas with a limited quantity of ambient air to
counteract the condensation of vapour inside the machine.
The gas ballast valve has an influence on the ultimate pressure of the machine, see
Technical Data [►29].
A ball valve enables to open or close the gas ballast flow.
2.5.2 Silencer
A silencer at the discharge connection (OUT) can be provided to reduce the exhaust
gas noise.
2.5.3 Barrier Gas System
The barrier gas system allows the supply of compressed air or nitrogen into the motor
side shaft seals in order to improve the sealing efficiency.
2.5.4 Mechanical Seals
The sealing systems can be equipped with mechanical seals. The following variants
are possible:
– Oil lubricated single mechanical seals on the motor side and labyrinth seals on the
suction side.
– Oil lubricated single mechanical seals on the motor side and suction side.

3 | Transport
8 / 32 Instruction Manual COBRA NC 1000 B WCV_EN_en
3 Transport
WARNING
Suspended load.
Risk of severe injury!
• Do not walk, stand or work under suspended loads.
WARNING
Lifting the machine using the motor eye bolt.
Risk of severe injury!
• Do not lift the machine using the eye bolt fitted to the motor. Only lift the machine as
shown.
NOTICE
In case the machine is already filled with oil.
Tilting a machine that is already filled with oil can cause large quantities of oil to
ingress into the cylinder.
• Drain the oil prior to every transport or always horizontally transport the machine.
Machine weight:
see the technical data or the nameplate (NP)
• Check the machine for transport damage.
If the machine is secured to a base plate:
• Remove the machine from the base plate.
4 Storage
• Seal all apertures with adhesive tape or reuse provided caps.
If the machine is to be stored for more than 3 months:
• Wrap the machine in a corrosion inhibiting film.
• Store the machine indoors, dry, dust free and if possible in original packaging
preferably at temperatures between 5 ... 55 °C.

Installation | 5
Instruction Manual COBRA NC 1000 B WCV_EN_en 9 / 32
NOTICE
Long storage time.
Risk of damage to the machine!
• If the machine is equipped with oil lubricated mechanical seals, we recommend to
completely fill the oil chamber before a long storage, see “Oil filling” in chapter Oil
Change [►21]. This protects the mechanical seals during a long storage. Use the
standard pump oil, see chapter Oil [►29].
• Before restarting the machine, drain the oil to the normal oil level, see “Oil draining”
in chapter Oil Change [►21].
5 Installation
5.1 Installation Conditions
NOTICE
Use of the machine outside of the permitted installation conditions.
Risk of premature failure!
Loss of efficiency!
• Take care that the installation conditions are fully complied with.
• Make sure that the environment of the machine is not potentially explosive.
• Make sure that the ambient conditions comply with the Technical Data [►29].
• Make sure that the environmental conditions comply with the protection class of the
motor and the electrical instruments.
• Make sure that the installation space or location is vented such that sufficient cool-
ing of the machine is provided.
• Make sure that cooling air inlets and outlets of the motor fan are not covered or ob-
structed and that the cooling air flow is not affected adversely in any other way.
• Make sure that the oil sight glass (OSG) remains easily visible.
• Make sure that enough space remains for maintenance work.
• Make sure that the machine is placed or mounted horizontally, a maximum of 1° in
any direction is acceptable.
• Check the oil level, see Oil Level Inspection [►20].
• Check the cooling liquid level, see Cooling Liquid Level Inspection [►21].
• Make sure that the cooling water complies with the requirements, see Cooling Wa-
ter Connection [►11].
If the machine is installed at an altitude greater than 1000 meters above sea level:
• Contact your Busch representative, the motor should be derated or the ambient
temperature limited.
5.2 Connecting Lines / Pipes
• Remove all protective covers before installation.
• Make sure that the connection lines cause no stress on the machine‘s connection; if
necessary use flexible joints.

5 | Installation
10 / 32 Instruction Manual COBRA NC 1000 B WCV_EN_en
• Make sure that the line size of the connection lines over the entire length is at least
as large as the connections of the machine.
In case of very long connection lines it is advisable to use larger line sizes in order to
avoid a loss of efficiency. Seek advice from your Busch representative.
5.2.1 Suction Connection
WARNING
Unprotected suction connection.
Risk of severe injury!
• Do not put hand or fingers in the suction connection.
NOTICE
Ingress of foreign objects or liquids.
Risk of damage to the machine!
If the inlet gas contains dust or other foreign solid particles:
• Install a suitable filter (5micron or less) upstream from the machine.
Connection size(s):
– DN125 PN16, EN 1092-1
If the machine is used as part of a vacuum system:
• Busch recommends the installation of an isolation valve in order to prevent the
machine from turning backwards.
5.2.2 Discharge Connection
Connection size(s):
At the machine discharge connection:
– DN125 PN16, EN 1092-1
At the silencer (SI) discharge connection (two optional versions available):
– DN125 PN16, EN 1092-1
– DN100 ISO-K, DIN 28404
• Make sure that the discharged gas will flow without obstruction. Do not shut off or
throttle the discharge line or use it as a pressurised air source.
• Make sure that the counter pressure (also termed back pressure) at the discharge
connection (OUT) does not exceed the maximum allowable discharge pressure,
see Technical Data [►29].

Installation | 5
Instruction Manual COBRA NC 1000 B WCV_EN_en 11 / 32
5.2.3 Cooling Water Connection
CWI CWOPHE
CWI Cooling water inlet CWO Cooling water outlet
PHE Plate heat exchanger
• Connect the cooling water connections (CWI / CWO) to the water supply.
Connection size:
– G1/2, ISO 228-1 (CWI / CWO)
• Make sure that the cooling water complies with the following requirements:
Supply capacity l/min 15
Water pressure bar 1 ... 6
Supply temperature °C +5 ... +30
Required pressure differential across sup-
ply and return
bar ≥ 1
• To reduce the maintenance effort and ensure a long product lifetime we recom-
mend the following cooling water quality:
Hardness mg/l (ppm) < 90
Properties Clean & clear
PH value 7 ... 8
Particle size µm < 200
Chloride mg/l < 100
Electrical conductivity µS/cm ≤ 100
Free chloride mg/l < 0.3
Materials in contact with the cooling water Stainless steel
NOTE
Water hardness unit conversion.
1 mg/l (ppm) = 0.056 °dh (german degree) = 0.07 °e (english degree) = 0.1 °fH (french
degree)

5 | Installation
12 / 32 Instruction Manual COBRA NC 1000 B WCV_EN_en
5.2.4 Barrier Gas System Connection (Optional)
Without nitrogen panel
PRV FRBGCMANFME
BGC Barrier gas connection FME Flow meter
FR Flow regulator MAN Manometer
PRV Pressure regulating valve
• Connect the barrier gas connection (BGC) to the gas supply.
Connection size:
– G1/4, ISO 228-1
• Make sure that the gas complies with the following requirements:
Gas type Dry nitrogen or air
Gas temperature °C 0 ... 60
Maximum gas pressure bar 13
Recommended pressure setting at the
pressure regulating valve (PRV)
bar 3
Filtration µm 5
Recommended flow rate SLM* 30
Air quality (only for air) Acc. to ISO
8573-1
Class 5.4.4.
* standard litre per minute
5.3 Filling Oil
NOTICE
Use of an inappropriate oil.
Risk of premature failure!
Loss of efficiency!
• Only use an oil type which has previously been approved and recommended by
Busch.

Installation | 5
Instruction Manual COBRA NC 1000 B WCV_EN_en 13 / 32
For oil type and oil capacity see Technical Data [►29] and Oil [►29].
1
2
Busch Oil
3
MAX
MIN
3 mm
4
Check oil level
Oil filling at the motor side
1
2
Busch Oil
3
MAX
MIN
3 mm
4
Check oil level
Oil filling at the suction side

5 | Installation
14 / 32 Instruction Manual COBRA NC 1000 B WCV_EN_en
When the oil filling is achieved:
• Write down the oil change date on the sticker.
Last oil change
__ / __ / ____
Oil type see nameplate
Change interval see
instruction manual
If there is no sticker (part no. 0565 568 959) on the machine:
• Order it from your Busch representative.
5.4 Filling Cooling Liquid
For cooling liquid type and cooling liquid capacity see Technical Data [►29] and
Cooling Liquid [►29].
1
2
Cooling
liquid
Zitrec M-25
3
MAX
MIN
4
Check cooling liquid level

Installation | 5
Instruction Manual COBRA NC 1000 B WCV_EN_en 15 / 32
5.5 Fitting the Coupling
E
Coupling hub (machine side) Coupling hub (motor side)Coupling spider
Radial screw
Max. admissible
torque: 10 Nm
Machine type Coupling size Value “E” (mm)
NC 1000 B ROTEX® 48 28
In case of a machine delivery without motor:
• Fit the second coupling hub on the motor shaft (separately delivered).
• Axially adjust the hub in such a way until value "E" is reached.
• When the coupling adjustment is done, lock the coupling hub by tightening the
radial screw.
• Mount the motor on the machine by including the coupling spider.
For further coupling information, go to www.ktr.com and download the instruction man-
ual of the ROTEX® coupling.
5.6 Electrical Connection
DANGER
Live wires.
Risk of electrical shock.
• Electrical installation work must only be executed by qualified personnel.
• Make sure that the power supply for the motor is compatible with the data on the
nameplate of the motor.
• The electrical installation must comply with applicable national and international
standards.
• Provide a lockable disconnect switch on the power line so that the machine is com-
pletely secured during maintenance tasks.
• Provide an overload protection according to EN 60204-1 for the motor.
• Make sure that the motor of the machine will not be affected by electric or electro-
magnetic disturbance from the mains; if necessary seek advice from Busch.
• Connect the protective earth conductor.
• Electrically connect the motor.

5 | Installation
16 / 32 Instruction Manual COBRA NC 1000 B WCV_EN_en
NOTICE
The admissible motor nominal speed exceeds the recommendation.
Risk of damage to the machine!
• Check the admissible motor nominal speed (nmax) on the nameplate of the machine
(NP).
• Make sure to comply with it.
• Consult the Technical Data [►29] to get more information.
NOTICE
The motor frequency is below 30 Hz.
Risk of damage to the machine!
• The motor nominal speed must always be higher than 1800 min-1 (30 Hz).
NOTICE
Incorrect connection.
Risk of damage to the motor!
• The wiring diagrams given below are typical. Check the inside of the terminal box
for motor connection instructions/diagrams.
5.6.1 Wiring Diagram Three-Phase Motor (Pump Drive)
Delta connection (low voltage): Star connection (high voltage):
NOTICE
Incorrect direction of rotation.
Risk of damage to the machine!
• Operation in the wrong direction of rotation can destroy the machine in a short time!
Prior to start-up, ensure that the machine is operated in the right direction.
The intended rotation direction of the motor is defined by the illustration below:
IN
• Jog the motor briefly.

Commissioning | 6
Instruction Manual COBRA NC 1000 B WCV_EN_en 17 / 32
• Watch the fan wheel of the motor and determine the direction of rotation just before
the fan wheel stops.
If the rotation of the motor must be changed:
• Switch any two of the motor phase wires.
5.7 Electrical Connection of the Monitoring Devices
NOTE
In order to prevent potential nuisance alarms, Busch recommends that the control sys-
tem is configured with a time delay of at least 20 seconds.
5.7.1 Wiring Diagram Resistance Thermometer
Part no.: 0651 552 252
Connector: M12x1, 4-pin
U = 7.5 … 30 VDC
4 ... 20 mA ► -50 ... 150 °C
Trip signal: Ttrip: 70 °C
1 2
4 3
3
1
+
-
1 = Brown ; 3 = Blue
5.7.2 Wiring Diagram Level Switch
Part no.: 0652 569 236
Connector: M12x1, 4-pin
U = 10 … 30 VDC (DC-PNP)
Imax = 200 mA
Contact: Normally closed
1 2
4 3
(+)
1
3
4(-)
0.5 A
1 = Brown ; 3 = Blue ; 4 = Black
Switch point:
Ltrip ► pin 1 + 4 ► low level “stop the machine”
6 Commissioning
NOTICE
The machine can be shipped without oil.
Operation without oil will ruin the machine in short time!
• Prior to commissioning, the machine must be filled with oil, see Filling Oil [►12].
NOTICE
The machine can be shipped without cooling liquid.
Operation without cooling liquid will ruin the machine in short time!
• Prior to commissioning, the machine must be filled with cooling liquid, see Filling
Cooling Liquid [►14].

6 | Commissioning
18 / 32 Instruction Manual COBRA NC 1000 B WCV_EN_en
NOTICE
Lubricating a dry running machine (compression chamber).
Risk of damage to the machine!
• Do not lubricate the compression chamber of the machine with oil or grease.
CAUTION
During operation the surface of the machine may reach temperatures of more than
70°C.
Risk of burns!
• Avoid contact with the machine during and directly after operation.
CAUTION
Noise of running machine.
Risk of damage to hearing!
If persons are present in the vicinity of a non noise insulated machine over extended
periods:
• Make sure that ear protection is being used.
• Make sure that the installation conditions (see Installation Conditions [►9]) are
met.
• Turn on the water supply.
If the machine is equipped with a barrier gas system:
• Turn on the barrier gas supply.
• Adjust the barrier gas pressure and volume flow.
• Switch on the machine.
• Make sure that the maximum permissible number of starts does not exceed 6 starts
per hour. Those starts should be spread within the hour.
• Make sure that the operating conditions comply with the Technical Data [►29].
• After a few minutes of operation, perform an Oil Level Inspection [►20].
• After a few minutes of operation, perform a Cooling Liquid Level Inspection [►21].
As soon as the machine is operated under normal operating conditions:
• Measure the motor current and record it as reference for future maintenance
and troubleshooting work.

Maintenance | 7
Instruction Manual COBRA NC 1000 B WCV_EN_en 19 / 32
6.1 Conveying Condensable Vapours
The machine, equipped either with a gas ballast valve or a dilution gas system, is suit-
able for the conveyance of condensable vapours within the gas flow.
If condensable vapours are to be conveyed:
START
Open the gas ballast
valve* or the
dilution gas sytem*
(solenoid valve)
Warm up the
machine
30 minutes 30 minutes
• Open the inlet
valve
• Perform the
process
• Close the inlet
valve
Close the gas ballast
valve*
or
the dilution gas
system*
END
* optional
accessories
• Continuously drain condensate from the condensate drain plug (CD) of the silencer
(SI) (Optional).
7 Maintenance
WARNING
Machines contaminated with hazardous material.
Risk of poisoning!
Risk of infection!
If the machine is contaminated with hazardous material:
• Wear appropriate personal protective equipment.
CAUTION
Hot surface.
Risk of burns!
• Prior to any action requiring touching the machine, let the machine cool down first.
NOTICE
Using inappropriate cleaners.
Risk of removing safety stickers and protective paint!
• Do not use incompatible solvents to clean the machine.
CAUTION
Failing to properly maintain the machine.
Risk of injuries!
Risk of premature failure and loss of efficiency!
• Respect the maintenance intervals or ask your Busch representative for service.

7 | Maintenance
20 / 32 Instruction Manual COBRA NC 1000 B WCV_EN_en
• Shut down the machine and lock against inadvertent start up.
• Turn off the water supply.
If the machine is equipped with a barrier gas system:
• Close the barrier gas supply.
• Vent the connected lines to atmospheric pressure.
If necessary:
• Disconnect all connections.
7.1 Maintenance Schedule
The maintenance intervals depend very much on the individual operating conditions.
The intervals given below are considered as starting values which should be short-
ened or extended as appropriate. Particularly harsh applications or heavy duty opera-
tion, such as high dust loads in the environment or in the process gas, other contami-
nation or ingress of process material, can make it necessary to shorten the mainte-
nance intervals significantly.
Interval Maintenance work
Monthly • Check the oil level, see Oil Level Inspection
[►20].
• Check the cooling liquid level, see Cooling Liquid
Level Inspection [►21].
• Check the machine for oil leaks - in case of leaks
have the machine repaired (contact Busch).
Yearly • Carry out a visual inspection and clean the machine
from dust and dirt.
• Check the electrical connections and the monitoring
devices.
Yearly
In case of those accessories
being installed.
• Check the filter of the gas ballast valve (GB) and
change it if necessary, see Replacing the Gas Ballast
Filter (Optional) [►21].
• Check the silence (SI) and clean it if necessary.
Every 5000 hours, at the least
after 1 year
• Change the oil of the gear and bearing housings
(both sides), see Oil Change [►21].
• Change the cooling liquid, see Cooling Liquid
Change [►24].
• Clean the magnetic plugs (MP).
Every 16000 hours, at the
least after 4 years
• Have a major overhaul on the machine (contact
Busch).
7.2 Oil Level Inspection
• Shut down the machine.
• When the machine is stopped, wait 1 minute before checking the oil level.
MAX
MIN
3 mm
MAX
MIN
3 mm
MAX
MIN
3 mm
• Make sure that the oil level is between the middle of the oil sight glass and 3mm
above it.