ROTORCOMP NK 31 User manual

Installation and operating manual
[en] 02/2014
SCREW COMPRESSOR COMPACT MODULE
NK 31
Original operating manual

© Copyright ROTORCOMP VERDICHTER GmbH, 2014
All rights reserved.
No duplication, modication or translation beyond the degree permitted by the applicable copyright laws
is permitted without prior written approval.
The information contained in this document is subject to change without prior notice.
This document is not subject to the change service.
ROTORCOMP VERDICHTER GmbH
Industriestraße 9
82110 Germering
Germany

i.1
[en] 02/2014
Installation and operating manual - NK 31
1 Foreword............................................ 1.1
1.1 General ............................................... 1.1
1.2 Scope.................................................. 1.1
1.3 Change service................................... 1.1
1.4 Abbreviations ...................................... 1.1
1.5 Manufacturer’s information ................. 1.1
1.5.1 General information ............................ 1.1
1.5.2 Purpose............................................... 1.2
1.5.3 Standard delivery scope ..................... 1.2
1.6 Warranty information,
liability disclaimer................................ 1.2
1.7 Nameplate........................................... 1.2
2 Safety precautions............................ 2.1
2.1 Marking of safety precautions............. 2.1
2.2 Safety regulations ............................... 2.1
2.3 General safety precautions................. 2.1
2.3.1 Special symbols.................................. 2.2
2.3.2 Instructions to use safety equipment .. 2.2
3 Technical Description....................... 3.1
3.1 General overview of NK 31
Screw Compressor Compact Module
(standard model with electric control
unit)..................................................... 3.1
3.2 Flow diagram of NK 31
(electric control unit)............................ 3.2
3.3 Operating description for NK 31
Screw Compressor Compact Module
(electric) .............................................. 3.2
3.3.1 Standstill ............................................. 3.2
3.3.2 Relieved stating .................................. 3.3
3.3.3 Feed phase......................................... 3.3
3.3.4 Switching off........................................ 3.3
3.4 General overview of NK 31
Screw Compressor Compact Module
(standard model with pneumatic
control unit) ......................................... 3.4
3.5 Flow diagram of NK 31
(pneumatic control unit) ...................... 3.5
3.6 Operating description for NK 31
Screw Compressor Compact Module
(pneumatic)......................................... 3.5
3.6.1 Standstill ............................................. 3.5
3.6.2 Starting................................................ 3.6
3.6.3 Switching off........................................ 3.6
3.7 Flow diagram of NK 31
(START-STOP controller).................... 3.7
3.8 Operating description for NK 31
Screw Compressor Compact Module
(START-STOP controller).................... 3.7
3.8.1 Standstill ............................................. 3.7
3.8.2 Load condition..................................... 3.8
3.8.3 Switching off........................................ 3.8
3.9 Intake valve......................................... 3.9
3.9.1 Installation position ............................. 3.9
3.10 Intake air lter ................................... 3.10
3.10.1 Micro air lter element....................... 3.10
3.10.2 Intake lter monitoring....................... 3.10
3.11 Fine separator....................................3.11
3.11.1 Oil intake non-return valve.................3.11
3.11.2 Fine separator cartridge.................... 3.12
3.11.3 Minimum pressure valve................... 3.13
3.12 Air-oil circulation outside
compressor module .......................... 3.14
3.12.1 Oil lter.............................................. 3.15
3.12.2 Oil thermostat.................................... 3.15
3.13 Oil cooler/air after-cooler (option) ..... 3.16
3.14 Safety valve (SIV) (option)................ 3.16
4 Transport ........................................... 4.1
4.1 Delivery and packing........................... 4.1
4.2 Transport damage............................... 4.1
4.3 Transporting unpacked system........... 4.2
4.4 Transport options ................................ 4.2
5 Installation/Assembly....................... 5.1
5.1 Connection thread/assembly .............. 5.1
5.1.1 Fastening screws................................ 5.1
5.1.2 Pipe connections................................. 5.1
5.2 Safety precautions for installation
and assembly...................................... 5.1
5.3 Installation........................................... 5.2
5.3.1 Fastening on base frame with
screw tting......................................... 5.2
5.3.2 Drive.................................................... 5.2
5.4 Belt drive............................................. 5.3
5.5 Direct drive.......................................... 5.3
5.6 Air outlet.............................................. 5.4
5.7 Oil cooling ........................................... 5.4
5.8 Service................................................ 5.4
6 Commissioning................................. 6.1
6.1 Preparation for commissioning ........... 6.1
6.2 Checking direction of rotation ............. 6.1
6.3 Test run ............................................... 6.1
6.4 Recommissioning screw compressor
system................................................. 6.2
Contents

i.2 [en] 02/2014
Installation and operating manual - NK 31ROTORCOMP VERDICHTER
7 Maintenance ...................................... 7.1
7.1 Safety precautions .............................. 7.1
7.2 Oil level ............................................... 7.2
7.2.1 Oil level check via oil ller opening ..... 7.2
7.3 Oil change........................................... 7.3
7.3.1 Oil change intervals ............................ 7.3
7.3.2 Oil drain points.................................... 7.3
7.3.3 Filling with oil....................................... 7.4
7.4 Oil lter................................................ 7.4
7.4.1 Oil lter replacement intervals............. 7.4
7.4.2 Oil lter replacement........................... 7.4
7.5 Fine separator cartridge...................... 7.5
7.5.1 Maintenance intervals......................... 7.5
7.5.2 Replacing ne separator cartridge...... 7.5
7.6 Intake air lter ..................................... 7.6
7.6.1 Maintenance intervals......................... 7.6
7.6.2 Replacing air lter element ................. 7.6
7.7 Maintenance check sheet ................... 7.7
7.8 Maintenance intervals......................... 7.8
8 Lubricants
and Operating Materials
Maintenance Parts ............................ 8.1
8.1 Lubricants and operating materials..... 8.1
8.1.1 Oil recommendation............................ 8.1
8.1.2 Topping up oil...................................... 8.1
8.1.3 Measures at low room temperature .... 8.1
8.1.4 Piping materials .................................. 8.1
8.1.5 Pressure dew point of
compressed air ................................... 8.2
8.1.6 Temperatures ...................................... 8.2
8.1.7 Condensate damage........................... 8.2
8.1.8 Cold starts........................................... 8.2
8.1.9 Oil separation...................................... 8.3
8.1.10 Multigrade oil....................................... 8.3
9 Technical Data and
Tightening Torques........................... 9.1
9.1 Technical data ..................................... 9.1
9.2 Tightening torques .............................. 9.2
10 Troubleshooting.............................. 10.1
Contents

1.1
[en] 02/2014
Installation and operating manual - NK 31
1.1 General
This manual contains information and regulations
for the installation and operation of the NK 31
Screw Compressor Compact Module.
1.2 Scope
This documentation is applicable for the screw
compressor of the type NK 31 Compact Module
from the delivery date of 01/2008.
1.3 Change service
This document is not subject to the change ser-
vice.
1.4 Abbreviations
bar (g) Operating pressure
(relative pressure in bar)
Bh Operating hours
DHV Minimum pressure valve
RC ROTORCOMP
SIV Safety valve
Min. minimum
Max. maximum
V DC Direct voltage
V AC Alternating voltage
1.5 Manufacturer’s information
1.5.1 General information
This operating manual provides information on
the mode of operation, installation, operation and
maintenance of the NK 31. It is must therefore
always be consulted on the operation and main-
tenance of the NK 31.
Read this operating manual carefully before com-
missioning the NK 31 for the rst time in order to
ensure proper handling, operation and mainte-
nance from the outset.
Pay particular attention to all warnings and safety
precautions.
ROTORCOMP screw compressors are carefully
checked and tested prior to shipping. When your
compressor arrives, the delivery scope must be
checked for completeness and damage.
Any missing parts and/or transport damage must
be reported immediately. A damaged compressor
module must not be put into operation under any
circumstances.
Always have the operating manual available for
the operating personnel and make sure that op-
eration and maintenance are carried out accord-
ing to the instructions.
All instructions contained in this operating manu-
al must be observed in the specied manner and
sequence in order to prevent injuries and dam-
age to the system.
The screw compressor has been built accord-
ing to the latest technology and the recognized
safety rules.
Danger may nevertheless result for the user or
others or for the compressor system during its
use.
Any use other than described in the chapter “Pur-
pose” is considered improper.
ROTORCOMP shall not be liable for any damage
or injuries resulting from such improper use.
We shall not provide any guarantee whatsoever
for malfunctions and damage resulting from fail-
ure to comply with the operating manual.
The manufacturer reserves the right to carry
out further technical developments without prior
notice.
Always specify the model and the complete serial
number from the nameplate in all correspon-
dence.
ROTORCOMP shall assume no liability whatso-
ever for damage or injuries which occur during
handling, operation, maintenance work or repairs
due to a failure to comply with the safety instruc-
tions to proceed with the usual care and caution,
even if this is not expressly mentioned in this
operating manual.
1 Foreword

1.2 [en] 02/2014
Installation and operating manual - NK 31ROTORCOMP VERDICHTER
1.5.2 Purpose
The NK 31 is a screw compressor compact mod-
ule designed for installation in a compressed-air
generating station.
The sole intended use of the system is the
compression of atmospheric air. The NK 31 may
only be used to compress gases or other media
following written approval by ROTORCOMP.
The NK 31 may only be installed by specialized
companies with the corresponding know-how.
The safety precautions, technical data, limits, in-
stallation guidelines and regulations for commis-
sioning and operation specied in this operating
manual must be observed and complied with.
1.5.3 Standard delivery scope
With the NK 31, ROTORCOMP offers a com-
pletely equipped, compact compressor module.
The components of the standard delivery scope
are described in the following chapters.
Optionally available components are marked with
(optional).
1.6 Warranty information,
liability disclaimer
ROTORCOMP is a manufacturer of screw com-
pressor components and not of ready-to-operate
compressor systems.
RC shall only be answerable for any defects of
these individual components for which it is re-
sponsible within the scope of the warranty condi-
tions.
Failure to comply with the following instructions
and information shall void any and all liability.
This liability disclaimer also results in the loss of
claims for damages. This applies in particular in
case of:
– Installation not approved by RC
– Improper use
– Operation of the compressor outside the speci-
ed limits
– Failure to observe the safety precautions and
the usual care and caution
– Unsuitable operating materials (gases, oils)
– Condensate in the screw compressor
– Corrosion as subsequent damage
– Improper operation
– Insufcient maintenance, missing proof of
maintenance
– Use of unsuitable tools
– Failure to use genuine spare parts
– Unauthorized modications to the screw com-
pressor module and/or its components–
1.7 Nameplate
For the location of the nameplate, see Figure 3-1
or 3-3.
Should you have questions, please provide us
with the data on the nameplate. This ensures that
you receive the correct information.
Figure 1-1
Stamping for customers outside Germany
(Europe)
1. Order No.
2. Model
3. Serial No.
4. Year of manufacture
5. Max. rpm
6. Max. operating pressure in psi
7. Max. operating temperature °F
8. Max. operating temperature °C
9. Max. operating pressure in bar
1 2 3 4
5
6
7
9 8

2.1
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Installation and operating manual - NK 31
2.1 Marking of safety precautions
Important instructions concerning hazards to per-
sons, technical safety and their operational safety
are especially highlighted in the following.
They precede the measures to be taken and
have the following meaning:
Warning
Indicates working and operating processes which
must be exactly complied with in order to prevent
endangering of persons. These include infor-
mation on special dangers when handling the
system.
Attention
Refers to working and operating processes which
must be exactly complied with to prevent damage
to or destruction of parts or all of the system.
Note
Indicates special information for better handling
during operating, inspection and adjustment pro-
cesses and care work.
2.2 Safety regulations
The regulations of the respective country for put-
ting into service and operating pressure vessels
must be observed. In Germany these include:
– Directive 97/23/EC (Pressure Vessel Directive
DGRL) of 05/29/1997
– Operating Safety Ordinance (BetrSichV)
of 09/27/2002
2.3 General safety precautions
This operating manual contains important instruc-
tions and information on the installation, com-
missioning, operation and maintenance, which
must be observed by the owner. As a result, it is
absolutely necessary to turn over the entire docu-
mentation to the specially trained personnel of
the owner or to make it available at the operating
location prior to installation and commissioning.
Prior to installation and commissioning, the entire
operating manual must be carefully read by the
specially trained personnel and then kept in a
safe place. Failure to observe the safety precau-
tions can result in a serious hazard for the per-
sonnel, the pressure vessel or the environment.
Observe the chapter “Manufacturer’s information”
on page 1-1 of this operating manual.
The following safety precautions only refer to the
NK 31 screw compressor module and not to the
entire compressor system.
The applicable national safety and occupational
safety regulations of the respective country in
which the system is operated must be complied
with.
The manufacturer of the compressor system is
responsible for including the necessary safety
regulations for the operation of the compressor
system in the operating manual of the compres-
sor system.
Installation, operation, maintenance and repair
may only be carried out by authorized, trained
and qualied personnel.
The operating personnel is expected to safely
use the working technology and follow all ap-
plicable local operating safety regulations and
provisions.
The owner bears the responsibility for always
keeping the machine in safe operating condition.
Limits (pressures, temperatures, time settings,
etc.) must be permanently marked.
Should a regulation contained in this list, espe-
cially with regard to safety, not comply with legal
regulations, then the safer of the two applies.
2 Safety precautions

2.2 [en] 02/2014
Installation and operating manual - NK 31ROTORCOMP VERDICHTER
2.3.1 Special symbols
Do not operate the system without the
safety device mounted
Do not inhale compressed air from this
machine
Warning:
System can be started automatically
via remote control following a power
failure
Warning:
System runs on for 30 seconds after
the "OFF" button is pressed
Watch cooling air
Warning:
Do not operate the system if the doors
are open or the shrouding is loose.
Warning:
Hot machine parts
Warning:
Part under pressure
Lifting point
Warning:
High voltage
Active environmental protection
Warning on a danger point
Warning:
Danger of explosion and/or detonation
Warning:
Hazardous substances
Warning:
Flammable substances
2.3.2 Instructions to use safety
equipment
Wear safety helmet
Wear safety shoes
Wear personal safety equipment
(safety goggles, protective gloves,
safety clothing, etc.) in accordance with
the local safety regulations
Read the operating manual before
initial operation, maintenance, service
and repairs.

3.1
[en] 02/2014
Installation and operating manual - NK 31
1. Name plate
2. Intake valve with intake lter unit
3. Safety valve (optional)
4. Separator cartridge
5. Minimum pressure valve
6. Compressed air outlet
7. Control block, electric
8. Oil sight glass (optional), oil level control
9. Temperature probe connection
10. Oil-Thermostat
3 Technical Description
4
5
6
7
19
18
12 11 10 8
1617 14 15 13 9
1 32
Figure 3-1
3.1 General overview of NK 31 Screw Compressor Compact Module
(standard model with electric control unit)
11. Oil circuit / outlet
12. Oil circuit / inlet
13. Oil lter
14. Oil drain plug
15. Oil ller
16. NK 31 basic module
17. Front cover
18. Drive shaft
19. Direction of rotation

3.2 [en] 02/2014
Installation and operating manual - NK 31ROTORCOMP VERDICHTER
1. Intake lter
2. Intake valve
2.1 No-load nozzle
3. Control unit (electric)
3.1 Solenoid valve
4. Screw compressor
5. Separator tank with pre-separation
6. Fine separator
7. Minimum pressure valve
8. Oil thermostat
9. Oil lter
10. Oil cooler
11. Air after-cooler
12. Non-return valve
13. Safety valve (optional)
2.1
1
2
45
3
3.1
13
6
711
9
8
10
12
Figure 3-2
3.2 Flow diagram of NK 31
(electric control unit)
3.3 Operating description for NK 31
Screw Compressor Compact Module
(electric)
The ow diagram shows a schematic view of the
operating principle and the arrangement of the
main components of the NK 31 screw compres-
sor module with electrical control unit, regardless
of any other equipment.
3.3.1 Standstill
At standstill the solenoid valve 3.1 is deener-
gized, the relief line is open and the downstream
devices are depressurized. The minimum pres-
sure valve 7set to approx. 5.5 bar at the factory
is tightly closed. The intake valve 2is slightly
open at standstill.

3.3
[en] 02/2014
Installation and operating manual - NK 31
3.3.4 Switching off
When the system is switched off, the intake
valve 2, operates, supported by spring pressure,
as an independent non-return valve. After being
switched off, the deenergized solenoid valve 3.1
also opens and compressed air ows into the
control piston of the intake valve 2. The intake
opening is closed off oil-tight in the process, and
then the system is completely relieved via the no-
load/ relief nozzle 2.1 (see Figure 3-5).
3.3.2 Relieved stating
During relieved starting a small air quantity is
already drawn in at a minimum vacuum by the ro-
tor rotation. This air quantity is then compressed
and ows as pilot air via the deenergized, open
solenoid valve 3.1 under the piston of the control
valve. The intake valve 2closes and remains in
the no-load position. In this throttled position a
corresponding air quantity is drawn in at a certain
compressor rotational speed so that a residual
pressure of approx. 2 bar is maintained in the
separator tank 5. The compressed air ows into
the intake lter 1via the no-load nozzle 2.1 of the
intake valve 2to relieve the system.
3.3.3 Feed phase
During the feed phase the solenoid valve 3.1
is closed electrically. The control pressure of
the intake valve 2is released via the no-load
nozzle 2.1. The intake valve 2opens due to the
spring force and the vacuum in the intake cham-
ber of the compressor. The air drawn in ows via
the intake lter 1through the intake valve 2di-
rectly into the compression chamber of the screw
compressor 4. There the intake air is compressed
and oil for lubrication and cooling is injected.
The oil-air mixture then enters the separator
tank 5 in which the majority of the oil is separated
from the air. The air then ows via the ne sepa-
rator 6and the minimum pressure valve 7to the
compressed air outlet.
In the ne separator 6 the oil is ltered out down
to a residual content of < 3 mg/m3and then
routed back into the compressor housing via a
nozzle and a non-return valve 12.
When the compressor is switched off, the mini-
mum pressure valve 7 with a non-return function
prevents backow of the compressed air out of
the system into the compression chamber in the
discharge phase.
During startup a faster pressure buildup is also
ensured, which is required for optimum lubrica-
tion and oil separation.
The heat resulting during compression is dis-
sipated via the oil-air mixture. The oil circulation
also results from the pressure difference between
the outlet and inlet pressure. The optimum oper-
ating temperature for the oil is adjusted by the oil
thermostat 8. Depending on the oil temperature,
the oil ow is routed directly via the oil cooler 10
or directly to the oil lter 9by the oil thermostat
valve.
The oil then ows via the oil lter 9to the various
injection points in the compressor block.

3.4 [en] 02/2014
Installation and operating manual - NK 31ROTORCOMP VERDICHTER
5
6
7
19
18
12 11 10 8
1617 14 15 13 9
1 2 43
Figure 3-3
3.4 General overview of NK 31 Screw Compressor Compact Module
(standard model with pneumatic control unit)
1. Name plate
2. Control unit, pneumatic
3. Intake valve with intake lter unit
4. Safety valve (optional)
5. Separator cartridge
6. Minimum pressure valve
7. Compressed air outlet
8. Oil sight glass (optional), oil level control
9. Temperature probe connection
10. Oil-Thermostat
11. Oil circuit / outlet
12. Oil circuit / inlet
13. Oil lter
14. Oil drain plug
15. Oil ller
16. NK 31 basic module
17. Front cover
18. Drive shaft
19. Direction of rotation

3.5
[en] 02/2014
Installation and operating manual - NK 31
Figure 3-4
3.5 Flow diagram of NK 31
(pneumatic control unit)
3.6 Operating description for NK 31
Screw Compressor Compact Module
(pneumatic)
The ow diagram shows a schematic view of the
operating principle and the arrangement of the
main components of the NK 31 screw compres-
sor module with pneumatic control unit, regard-
less of any other equipment.
3.6.1 Standstill
At a standstill the intake valve 2and the impulse-
pressure relief valve 3.2 are closed by the spring
pretension. The downstream devices are depres-
surized.
The minimum pressure valve 7is set to approx. 5
bar at the factory is tightly closed. The propor-
tional regulator 3.1 is set to operating pressure.
2.1
2
9
8
10
4 5
3 3.1
3.2
11
6
7
13
12
1
1. Intake lter
2. Intake valve
2.1 No-load nozzle
3. Control unit (pneumatic)
3.1 Proportional control valve
(positive)
3.2 Impulse-pressure relief valve
4. Screw compressor
5. Separator tank with pre-separation
6. Fine separator
7. Minimum pressure valve
8. Oil thermostat
9. Oil lter
10. Oil cooler
11. Air after-cooler
12. Non-return valve
13. Safety valve (optional)

3.6 [en] 02/2014
Installation and operating manual - NK 31ROTORCOMP VERDICHTER
3.6.2 Starting
During start-up, the intake valve 2already opens
at minimum vacuum in the intake chamber of the
screw compressor 4due to the rotor rotation. The
drawn in air ows via the intake lter 1through
the intake valve 2directly into the compression
chamber of the screw compressor 4. There the
intake air is compressed and oil is injected for
lubrication and cooling.
The oil-air mixture then enters the separator
tank 5 in which the majority of the oil is separated
from the air. The air then ows via the ne sepa-
rator 6and the minimum pressure valve 7to the
compressed air outlet.
In the ne separator 6 the oil is ltered out down
to a residual content of < 3 mg/m3and then
routed back into the compressor housing via a
nozzle and a non-return valve 12.
When the compressor is switched off, the mini-
mum pressure valve 7 with a non-return function
prevents backow of the compressed air out of
the system into the compression chamber in the
discharge phase.
During startup a faster pressure buildup is also
ensured, which is required for optimum lubrica-
tion and oil separation.
When the operating air pressure is reached, the
proportional regulator 3.1 opens and the pilot
air ows under the piston of the intake valve 2,
which begins to close. The adjustable proportion-
al regulator 3.1 steplessly controls the pressure
under the piston of the intake valve 2in depen-
dence on the compressed-air removal. This pres-
sure acts against the spring force and therefore
determines the valve stroke and the drawn-in
quantity of air.
The compress pilot air ows via the no-load
nozzle 2.1 of the intake valve 2back into the
compression chamber 4.
The heat resulting during compression is dis-
sipated via the oil-air mixture. The oil circulation
also results from the pressure difference between
the outlet and inlet pressure. The optimum oper-
ating temperature for the oil is adjusted by the oil
thermostat 8. Depending on the oil temperature,
the oil ow is routed directly via the oil cooler
10 or directly to the oil lter 9by the thermostat
valve.
The oil then ows via the oil lter 9to the various
injection points in the compressor block.
3.6.3 Switching off
When switching off the system, the intake valve 2
operates, supported by spring pressure, as an in-
dependent non-return valve and closes the intake
opening oil-tight.

3.7
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Installation and operating manual - NK 31
2
8
7
9
3410
5
6
12
11
1
Abbildung 3-5
3.7 Flow diagram of NK 31
(START-STOP controller)
1. Intake lter
2. Intake valve
3. Screw compressor
4. Separator tank with pre-separation
5. Fine separator
6. Minimum pressure valve
7. Oil thermostat
8. Oil lter
9. Oil cooler
10. Air after-cooler
11. Non-return valve
12. Safety valve (optional)
3.8 Operating description for NK 31
Screw Compressor Compact Module
(START-STOP controller)
The ow diagram shows a schematic view of the
operating principle and the arrangement of the
main components of the NK 31 screw compres-
sor module with pneumatic control unit, regard-
less of any other equipment.
In the start-stop controller there is no magnet
control or piston. The start-stop controller func-
tions only mechanically, through the pressure
difference.
3.8.1 Standstill
At standstill the intake valve is slightly open. The
minimum pressure valve 6is set at 5.5 bar and is
completely closed. The system is depressurized.

3.8 [en] 02/2014
Installation and operating manual - NK 31ROTORCOMP VERDICHTER
3.8.2 Load condition
The rotor rotation produces vacuum in the suc-
tion port which opens the untake valve 2.
The drawn in air ows via the intake lter 1
through the intake valve 2directly into the com-
pression chamber of the screw compressor 3.
There the intake air is compressed and oil is
injected for lubrication and cooling.
The oil-air mixture then enters the separator
tank 4 in which the majority of the oil is separated
from the air. The air then ows via the ne sepa-
rator 5and the minimum pressure valve 6to the
compressed air outlet.
In the ne separator 5 the oil is ltered out down
to a residual content of < 3 mg/m3and then
routed back into the compressor housing via a
nozzle and a non-return valve 11.
When the compressor is switched off, the mini-
mum pressure valve 6 with a non-return function
prevents backow of the compressed air out of
the system into the compression chamber in the
discharge phase.
During startup a faster pressure buildup is also
ensured, which is required for optimum lubrica-
tion and oil separation.
The heat resulting during compression is dis-
sipated via the oil-air mixture. The oil circulation
also results from the pressure difference between
the outlet and inlet pressure. The optimum oper-
ating temperature for the oil is adjusted by the oil
thermostat 7. Depending on the oil temperature,
the oil ow is routed directly via the oil cooler 9or
directly to the oil lter 8by the thermostat valve.
The oil then ows via the oil lter 8to the various
injection points in the compressor block.
3.8.3 Switching off
When the system is switched off pressure builds
up over the rotors and closes the intake valve 2
makeing an oil tight seal.
The remaining pressure is released progressively
via a pressure line from the ne separator 5to
a nozzle in the intake valve 2. Through this the
system is completely depressurized.

3.9
[en] 02/2014
Installation and operating manual - NK 31
AIntake valve opened
BIntake valve closed
1. Air inlet
2. Air outlet
3. Control line of intake valve
4. No-load/relief nozzle
Figure 3-6
3.9 Intake valve
The NK 31 is equipped with an integrated intake
valve mounted directly on the compressor hous-
ing.
3.9.1 Installation position
Figure 3-7
1
Different control units can be used for various
operating modes:
– the EMC electric control unit or
– the PMC pneumatic control unit
Depending on the application, various intake
control-valve systems can also be used.
A B
1
1
3
2
4

3.10 [en] 02/2014
Installation and operating manual - NK 31ROTORCOMP VERDICHTER
3.10 Intake air lter
Figure 3-8
3.10.1 Micro air lter element
The RC intake air lter is mounted directly over
the intake valve.
The micro air lter 1 with a neness of 10 μm is
used for the ltering of intake air.
The constant degree of separation of almost
100 % on all loading levels, the resistance to
heat, cold, water, oil and fuel and a large lter
area permit a long service life. As a result, the
micro air lter element is the ideal ne lter for
the ltering of intake air of compressor system.
1
3.10.2 Intake lter monitoring
• Maintenance indicator, optical (option)
• Maintenance indicator, electric (option)
The micro air lter elements are recommended
as a 1-stage lter with a low lter resistance for
standard applications.
Attention
Special applications, e.g. system installation in
a heavily soiled environment, mobile systems,
etc., require 2-stage lters with a somewhat
higher lter resistance, however a better degree
of separation for the protection of the compressor
system.
Filter Type/Order No.: on special request.

3.11
[en] 02/2014
Installation and operating manual - NK 31
1. Fine separator cartridge
2. Minimum pressure valve
3. Sight glass for oil separation
3.11.1 Oil intake non-return valve
Figure 3-10
The oil intake non-return valve 1 prevents ood-
ing of the ne separator cartridge with oil ow-
ing back out of the screw compressor due to
the pressure difference in the system when the
screw compressor system is switched off.
1
Figure 3-9
3.11 Fine separator
1
3
2

3.12 [en] 02/2014
Installation and operating manual - NK 31ROTORCOMP VERDICHTER
3.11.2 Fine separator cartridge
Figure 3-11
1. De-oiled compressed air
2. Post-separator
3. Fine separator
4. Pressure-resistant support pipe
5. Separated oil
6. Outlet of de-oiled air
7. Inlet of air-oil mixture
8. Sealing off
9. Pressure-resistant housing
2
3
4
1
5
8
9
76
The ne separator cartridge is used to recover
the extremely nely distributed residual oil in the
form of droplets following the pre-separation.
The ne separator cartridge separates virtually
the entire residual oil from the compressed air.
An optimum pre-separation in the separating tank
is assumed - the better the pre-separation, the
better the ne separation.
The vertical cartridge is owed against from be-
low, while the residual oil is separated out while
owing through the special lter element. Then it
is fed into the oil circulation again.