Knorr-Bremse ZB44 Series User manual

T5 T6
T7 T8
G2
20 l
20 l
211
22
23
24
29
0.25 l
0.25 l
0.25 l
0.25 l
Nozzle
Check valve
Pressure regulator
Pressurised air
18 Bar
ZB44..
type APU
G1
T1 T2
T3
T4
T9 T10
T11 T12
T13 T14
T15 T16
G3
G4
G5
G6
3
Ø nozzle defined in procedure
Used part of test bench
Unused part of test bench
Y025030 - (EN - Rev. 003)
NOVEMBER 2014
AIR PROCESSING UNIT
ZB44..
Service Manual

Disclaimer
The information contained herein is intended for the exclusive use of trained persons within the commercial vehicle industry, and must not be passed on
to any third party.
All recommendations regarding products and their servicing or usage are with reference to Knorr-Bremse products and should not be considered applicable
to products from other manufacturers.
This information does not purport to be all-inclusive and no responsibility is assumed as a result of its use. We cannot accept any liability nor offer any
guarantee regarding data accuracy, completeness or timeliness. The information does not represent any guarantee or ensured characteristics of the
Products or Systems described.
No liability can be accepted based on the information, its use, recommendations or advice provided. In no event may we be held liable for any damage or
loss except in the case of wilful intent or gross negligence on our part, or if any mandatory legal provisions apply.
This disclaimer is an English translation of a German text, which should be referred to for all legal purposes.
Any legal disputes arising from the use of this information shall be subject to German law.
Revision Details
Rev. 003 November 2014 Graphics updated to current parts, front cover reworked

3
Contents
Safety and Environment Guidelines . . . . . . . . . . . . . . . . . . 4
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 5
1.1 Service Intervals . . . . . . . . . . . . . . . . . . . . 5
1.2 Basic Principles . . . . . . . . . . . . . . . . . . . . 6
2. Components . . . . . . . . . . . . . . . . . . . . . . . . 9
Serviceable Components of the Air Processing Unit . . . . . . . . . . . . 9
3. Service Instructions . . . . . . . . . . . . . . . . . . . . . 10
3.1 Removal and Replacement of the Desiccant Cartridge (A) . . . . . . . 10
3.2 Removal and Replacement of the Heater Assembly (B) . . . . . . . . 11
3.3 Removal and Replacement of the Silencer Assembly (C). . . . . . . . 12
3.4 Removal of the Air Processing Unit from the Vehicle . . . . . . . . . 13
3.5 Removal and Replacement or Service of the Oil Separator Unit (D) . . . . 14
3.6 Disassembling and Assembling the Purge Valve (E) . . . . . . . . . 17
3.7 Disassembling and Assembling the Tyre Inflator (F) . . . . . . . . . 19
3.8 Replacement of the Double Pressure Sensor (H) . . . . . . . . . . 20
3.9 Removal and Replacement of the Time Switch Piston (I) . . . . . . . 21
3.10 Refitting the Air Processing Unit to the Vehicle . . . . . . . . . . 23
Contents

4
Safety and Environment Guidelines
Note: The safety advice listed below is applicable to general service and diagnostic work on braking systems. Also observe any recommendations from
the axle or vehicle manufacturer concerning towing, jacking-up and securing the vehicle.
Before and during working on or around compressed air systems and devices, the following precautions should be observed:
1 Always wear safety glasses when working with air pressure.
2 Never exceed the vehicle manufacturer’s recommended air pressures.
3 Never look into air jets or direct them at anyone.
4 Never connect or disconnect a hose or line containing pressure; it may whip as air escapes.
5 When removing or servicing a product, ensure all pressure related to the specific system it is contained in has been depleted to 0 bar. Be aware
that if the vehicle is equipped with an air dryer system, it can also contain air pressure along with its purge reservoir, if fitted, even after pressure has
been drained from the other reservoirs.
6 If it is necessary to drain the air pressure from reservoirs, etc., keep away from brake actuator push rods and levers since they may move as system
pressure drops. On vehicles fitted with air suspension, it is advised when undertaking such work, to support the chassis from sudden lowering and
therefore prevent any possibility of being trapped between the chassis and axle or ground.
7 Park the vehicle on a level surface, apply the parking brakes, and always chock the wheels as depleting vehicle air system pressure may cause the
vehicle to roll.
8 When working under or around the vehicle, and particularly when working in the engine compartment, the engine should be shut off and the ignition
key removed. Where circumstances require that the engine be running, EXTREME CAUTION should be taken to prevent personal injury resulting
from contact with moving, rotating, leaking, heated or electrically charged components. Additionally, it is advisable to place a clear sign on or near
the steering wheel advising that there is work in progress on the vehicle.
9 Examine all pipework for signs of kinks, dents, abrasion, drying out or overheating. Be aware that kinks in pipework may result in air pressure being
trapped in the pipework and associated equipment. Replacement hardware, tubing, hose, fittings, etc. must be of equivalent size, type and strength
as original equipment and be designed specifically for such applications and systems. Check the attachment of all pipework; it should be installed
so that it cannot abrade or be subjected to excessive heat.
10 Components with stripped threads or damaged/corroded parts must be replaced completely. Do not attempt repairs requiring machining or welding
unless specifically stated and approved by the vehicle or component manufacturer.
11 Never attempt to install, remove, disassemble or assemble a device until you have read and thoroughly understood the recommended procedures.
Some units contain powerful springs and injury can result if not properly dismantled and reassembled. Use only the correct tools and observe all
precautions pertaining to use of those tools.
12 Before removing any device note its position and the connections of all pipework so that the replacement/serviced device can be properly installed.
Ensure that adequate support or assistance is provided for the removal/installation of heavy items.
13 Use only genuine replacement parts, components and kits as supplied by Knorr-Bremse or the vehicle manufacturer.
14 The serviced or replaced product must be checked for correct function and effectiveness.
15 If products have been dismantled, serviced or replaced, whose performance could affect braking performance or system behaviour, this should
be checked on a roller dynamometer. Bear in mind that a lower performance may be experienced during the bedding-in phase if new brake pads/
linings and/or brake discs/drums have been fitted.
16 Prior to returning the vehicle to service, make certain that all components and the complete brake systems are leak free and restored to their proper
operating condition.
Welding
To avoid damage to electronic components when carrying out electrical welding, the following precautions should be observed:
1 In all cases, before starting any electrical welding, remove all connections from any electronic control units or modules, noting their position and the
order in which they are removed.
2 When re-inserting the electrical connectors (in reverse order) it is essential that they are fitted to their correct assigned position - if necessary this
must be checked by PC Diagnostics.
Disposal of Waste Equipment by Business Users in the European Union
Thissymbolontheproduct,packagingorinuserinstructions,indicatesthatthisproductmustnotbedisposedofwithothergeneralwaste.Instead,
it is your responsibility to dispose of the waste electrical and electronic parts of this product by handing them over to a company or organisation
authorised for the recycling of waste electrical and electrical equipment. For more information about arrangements for waste equipment
disposal please contact your Knorr-Bremse distributor or local Knorr-Bremse representative.

5
Introduction
1
1.1 Service Intervals
The service interval is the length of time from the vehicle
first entering service, or from the last service, until the point
in time – or distance travelled by the vehicle (whichever is
the earlier) – when it is recommended that the specified
braking system device is serviced using a genuine
Knorr-Bremse service kit or replaced with a new part, or in
the case of ABS subjected to a system functionality check.
This service interval is provided for preventative
maintenance purposes so as to minimize the probability of a
vehicle breakdown.
The service interval does not preclude the intermediate
testing of the device on the vehicle to ensure that it is
functioning in a correct manner, or the correct maintenance
of other devices in the system that may influence the
service interval.
The service interval can be influenced by the application
and the operating conditions of the vehicle. The following
service intervals are based on the assumption that each
device is positioned so it cannot be inadvertently abused
or that external rubber boots/seals are not exposed to
abnormal influences.
In general, Knorr-Bremse service kits contain all of the
components that can deteriorate with use, such as rubber
parts (O-rings, special seals, bonded inlet/exhaust valves,
exhaust flaps), plastic and metal parts (filter elements and
springs), fasteners and the correct grease. The range of
kits is designed to enable each device to be serviced in
part or completely.
Knorr-Bremse service kits are only designed for use with
genuine Knorr-Bremse devices and are only to be used
in the manner detailed in these service instructions.
After servicing, the device must also be checked in
accordance with Knorr-Bremse service instructions to
ensure correct operation before the vehicle is placed back
in service.
Additional checks
In addition to the above, and any legally required periodic
vehicle inspections, it is recommended that simple routine
inspections of a general nature are carried out to maintain
the braking system at a high level of functionality. These
simple routine inspections should be (1) the weekly checking
for excess water in the reservoirs by operation of the
reservoir drain valves, and (2) the 6 monthly / (50,000 km)
checking of the complete braking system for excessive air
leakage during a maximum pressure foot brake application
with the vehicle stationary and the parking brake released.
Service interval Service Notes
Refer to vehicle manufacturer.
30 000 km recommended.
Clean the oil separator and replace the O-Rings
(If necessary the service interval can be revised,
depending on the amount of oil carryover).
Failure of the air processing unit to purge
or non-replacement of the desiccant
cartridge at the recommended interval
can cause a reduction in the service
interval of downstream components.
Refer to vehicle manufacturer.
1 year recommended.
Replace the desiccant cartridge.
Replace the oil separator, if necessary.

6
Introduction
1
1.2 Basic principles
The ZB44.. range of air processing units combines
the functions of a conventional air dryer with those of a
pressure regulator and multi-circuit protection valve in one
monoblock housing.
1.2.1 Features
• Classic air drying functionality
• Multi-circuit protection valve functionality
• Integrated unloader function
• Integral safety function (air dryer)
• Exhaust safety function (Multi-circuit protection valve, EC)
• Two integrated pressure sensors (Optional)
• ESS Compressor control (Optional but recommended)
• Regeneration either via reservoir or by time switch
• High pressure tyre inflation with safety valve (Optional)
• System pressure tyre inflation (Optional)
• Air suspension supply (Optional)
• Heater (Optional)
• Oil separator (Optional)
• Silencer type (Optional)
1.2.2 Functionality
The air processing unit is fitted in the compressor discharge
line of an air braking system to remove water, dirt, carbon
and oil from the compressed air and therefore prevent it
entering the vehicle air reservoirs during the Charge phase.
It controls the system pressure (unloader function). It also
maintains a pre-set pressure in the unaffected circuits of a
multi circuit braking system in the event of a failure in one
circuit (multi-circuit protection valve function).
When the increasing air pressure in the braking system
reaches a preset value (cut-out pressure), the unloader
valve signals the purge valve to open and the air processing
unit enters the Purge phase. This allows the trapped dirt
and condensate to be expelled and the desiccant to be
regenerated with clean, dry air from a separate purge
reservoir or with air from the brake system using an integral
timer. During this phase, air delivered by the compressor is
discharged to atmosphere and does not enter the braking
system. When, due to normal usage, the air pressure in
the braking system drops, to the closing pressure of the
unloader valve, it signals the purge valve to close and the
Charge phase begins again.
1.2.3 Air dryer element
Drying function
During the Charge phase, compressed air enters the air
processing unit through port 1and passes through the
oil separator element to remove particles and oil from the
air using the cyclotron principle. This helps to maintain
the quality of the desiccant bed, prolonging its life and
effectiveness. It continues up the outside of the inner
desiccant cartridge and then passes down through the
desiccant bed to remove the water vapour. The now clean,
dry air opens the delivery check valve, flows through the
multi-circuit protection valve, and is delivered from ports
21, 22, 23 and 24 to charge the vehicle braking system.

7
Introduction
1
Unloader function
The pressure after the delivery check valve also flows to
the unloader valve. When the increasing system pressure
reaches the preset cut-out pressure, the unloader valve
sends a pressure signal to the purge valve.
Purge function
The pressure from the unloader valve causes the purge
valve to open which connects the initial drainage chamber
to atmosphere through exhaust port 3and the accumulated
condensate. Oil and solid matter is then ejected. If the
compressor control function is not used and the purge
valve is open, air from the compressor discharges directly to
atmosphere through the purge valve seat and exhaust port 3.
Regeneration function
The resulting drop in pressure in the initial drainage
chamber causes air to flow back through the desiccant
bed and allows the delivery check valve to close. At the
same time clean, dry air flows back through the desiccant
bed, collecting water from the desiccant and regenerating
it ready for the next Charge phase. The wet air then flows
down the outside of the inner desiccant cartridge and is
discharged to atmosphere through the exhaust port 3.
Subsequent operation of the braking system will cause
the downstream air pressure to fall. When the pressure
drops to the cut-in pressure, the pressure signal from the
unloader valve to the purge valve drops to zero and the
purge valve closes. The Charge phase will then begin
again and the braking system pressure will build.
For air processing units with time switch the compressed air
required for regeneration is taken from the supply air reser-
voirs mounted downstream in the system. The regeneration
time is determined by the pneumatic time switch and
depends on the supply volume and the operating pressure
of the pneumatic system. Air processing units without time
switch require a separate reservoir for the regenerating air,
the size of which depends on the system volume and the
cut-out pressure. During the Charge phase the separate
purge reservoir is charged through port 25.
Timing function (optional)
During the Charge phase, some of the clean dry air from
the desiccant bed passes through the timing choke and
charges the integral timing reservoir.
During the Purge phase, the loss of pressure in the inlet
cavity will close the delivery check valve. Some dry air
from the brake service reservoirs is permitted to return
through the multi-circuit protection valve then through the
purge choke. This air flows back through the desiccant
bed and the oil separator and collects water from the
desiccant regenerating it ready for the next charge cycle.
After a predetermined time, determined by the size of the
timing choke, the air pressure in the timing reservoir will
drop sufficiently for its piston to close and stop the return
feed from the brake system. This stops the purge phase,
but the compressor remains unloaded. The sizes of the
timing choke and the purge choke are designed to match
the system requirements such that the Purge phase is
completed well within the compressor off-load cycle and
sufficient air is returned to fully regenerate the desiccant.
1.2.4 Multi-circuit protection element
Basic function
The multi-circuit protection valve consists of four individual
pressure protection valves connected together in various
configurations and each having limited feedback capability.
Air is supplied through the delivery check valve in the
air dryer element, and is delivered from ports 21 - 24 to
circuits 1to 4respectively. Circuits 1and 2may have a
bypass feature (optional).
When the opening pressure of each valve element
is reached, the diaphragm will lift, allowing air to
flow past the valve seat into the respective delivery
port and to circuits 23 and 24 from circuits 21
and 22 depending on the valve configuration.
Due to air usage or leakage etc, when the falling pressure
reaches the closing pressure, the diaphragm will drop
and the supply-to-delivery path will close.
Opening pressure
The opening pressure is the pressure required to open a
valve element when the respective downstream circuit is
at zero pressure. If a circuit is not at zero pressure, the
downstream pressure will also be acting on the diaphragm.
This means that a lower pressure will be required to open
the valve element, i.e. the actual opening pressure is
dependent on the downstream pressure and is therefore
usually lower than the stated value for the valve.

8
Introduction
1
Static closing pressure
The static closing pressure is the pressure at which the
valve element will close in the event of slow air usage
(e.g. leakage) from any circuit while the compressor is not
charging. The closing pressure is determined by the area
of the diaphragm and the preload of the graduating spring.
It is always lower than the opening pressure.
Dynamic closing pressure
In the event of a rapid pressure drop in a circuit, the dynamic
closing pressure will be maintained in the other circuits.
It is always higher than the static closing pressure and is
determined by the rate of air pressure loss in the circuit,
the amount of air being recharged and by the reservoir
volume of the individual circuits.
Charging sequence
Parallel charging
This configuration is not designed to charge each circuit
sequentially. In an initially empty air system there is no fixed
opening sequence. This is particularly true if the system
is already partly charged since the opening pressure of
circuits 23 or 24 could be much lower than that for circuits
21 or 22. (See opening pressure section above). To ensure
circuit 21 or 22 open first and in a reasonable time, circuits
21 and 22 have a bypass feature.
Series charging
This configuration is designed so that at least one of the
circuits 21 and 22 will open before circuits 23 and 24.
Between circuit 21/22 and 23/24 there are non-return
valves. Circuits 21 and 22 may also have a bypass feature
to speed up the filling of these circuits.
Bypass
The bypass feature is an air passage in each circuit 21 and
22 which connects the supply to the respective delivery
ports (21 and 22) when their valve elements are closed. As
a result, pressure can build in the unaffected circuits and
they will charge normally. The connections have a small
non-return valve to prevent loss of air in the reverse direction.
Non-return valves
The non-return valves retain pressure in circuits 23 and 24
in the event of a pressure drop in circuits 21 and 22.
Exhaust safety function (EC function)
The exhaust safety function of the multi-circuit protection
valve ensures that once applied the spring brakes cannot
be released unless there is at least sufficient pressure in the
service brake system to achieve the prescribed residual
service braking performance of the laden vehicle.
General note regarding graphical content
All graphics contained in this document are for guidance
only and subsequently some parts may vary slightly in
appearance.

9
2
Item Description Comments / Variants
A Desiccant cartridge For standard applications
For low temperature applications (-45 ºC)
B Heater assembly
Heater 12 V 27x1
Heater 24 V 27x1
Heater 24 V Bayonet - ISO15170
C Silencer
D Oil separator Oil separator complete
Oil separator seals
E Purge valve For standard applications
For low temperature applications (-45°C)
F High pressure tyre inflator
H Double pressure sensor
I Time switch
Serviceable Components of the Air Processing Unit
Components
Part Identification and Service Kits
Exploded View
For Service Kit Part Number see
www.knorr-bremseCVS.com
B
I
E
F
H
D
A
C

10
3
3.1 Removal and Replacement of the Desiccant Cartridge (A)
Step Service task
Removal with the air processing unit still fitted to the vehicle
1 Before starting work on the vehicle please refer to the safety and environment guidelines on page 4.
2 Clean the outside of the air processing unit and its surroundings to prevent entry of dirt.
3 Vent the air processing unit cartridge by charging the compressed air system until the cut-out pressure of the
unloader valve has been reached and the air processing unit has subsequently purged.
4 Switch off the engine.
To remove the air processing unit from the vehicle please refer to section “Removal of the Air Processing Unit from the Vehicle”.
Removing the cartridge
1 Unscrew desiccant cartridge (1) counter-clockwise, using suitable strap wrench.
2 Remove O-ring (2).
3 Wipe the body with a clean rag. Protect the clean air chamber and cartridge mounting thread from dirt.
Fitting the cartridge
1 Lightly lubricate the gasket at the base of the new cartridge (1) with grease.
2 Lubricate new O-ring (2) with grease.
3 Fit O-ring (2) over the cartridge retaining thread.
4 Screw desiccant cartridge (1) up to stop.
5 Fully tighten desiccant cartridge (1) by turning a further ½ turn using a suitable strap wrench.
6 Refit (if necessary) the air processing unit to vehicle and check according to chapter 3.10.
7 Charge the air system to just below cut-out pressure and check the new desiccant cartridge for leakage.
Item Description Qty
1 Desiccant cartridge 1
2 O-ring 1
Service Steps
Part Identification
Service Instructions
For Service Kit Part Number see
www.knorr-bremseCVS.com
Note that component numbering may not correspond to that
shown on separate Service Kit leaflets.
1
2

11
3
Service Instructions
3.2 Removal and Replacement of the Heater Assembly (B)
Service Steps
Part Identification
Item Description Qty
1 Heater assembly 1
2 Screw 1
1
2M27x1 (12V & 24V) Bayonet - ISO15170
For Service Kit Part Number see
www.knorr-bremseCVS.com
Note that component numbering may not correspond to that
shown on separate Service Kit leaflets.
Step Service task
Removal of the heater assembly
1 Clean the outside of the air processing unit and the surroundings of the heater area.
2 Unscrew electrical connector locking ring and unplug connector (not shown).
3 Undo screw (2).
4 Remove heater assembly (1).
Replacement of the heater assembly
1 Fit new heater assembly (1) into body.
2 Tighten new screw (2) to a torque of 3.5 Nm.
3 Refit the electrical connector and hand tighten the locking ring (not shown).

12
3
Service Instructions
3.3 Removal and Replacement of the Silencer (C)
Part Identification
Service Steps
Step Service task
Removal of the silencer assembly
1 Remove silencer assembly (1)
Replacement of the silencer assembly
1 Locate new silencer assembly (1) over its spigot on the base of the air processing unit.
2 Lightly tap the silencer assembly (1) in the direction of the spigot so that it snaps into place.
3 Check the fixation of new silencer. Repeatedly charge and vent the air system between cut-out and cut-in
pressure. Silencer must not be blown out by venting air.
Item Description Qty
1 Silencer assembly 1
1
For Service Kit Part Number see
www.knorr-bremseCVS.com

13
3
Service Instructions
3.4 Removal of the Air Processing Unit from the Vehicle
Service Steps
Step Service task
1 Before starting work on the vehicle please refer to the safety checks on page 4.
2 Vent the system air pressure completely.
3 Disconnect air lines after noting which port they are connected to for correct reinstallation.
4 Unscrew and remove the three M12 mountings (bolts, Fig. 1 or nuts, see Fig. 2).
5 Remove the air processing unit and cover the ports to prevent entry of dirt.
Fig. 1 Fig. 2

14
3
Service Instructions
3.5 Removal and Replacement or Service of the Oil Separator Unit (D)
Item Kit Description Qty
1tOil separator unit 1
2t• O-ring Ø 92 x 2.5 mm 1
3t• O-ring Ø 42 x 2.5 mm 1
4tScrew M 4 x 40 mm 2
5t• O-ring Ø 33 x 5 mm 1
6 Desiccant cartridge 1
Part Identification and Service Kits
3
2
1
5
6
For Service Kit Part Number see
www.knorr-bremseCVS.com
Fig. 1
tOil Separator complete
• Oil Separator seals
Note that component numbering may not correspond to that
shown on separate Service Kit leaflets.

15
3
Service Instructions
Fig. 2 Fig. 3 Fig. 4
Fitting the oil separator
Step Service task
1Check that the sealing surfaces of the oil separator unit (1) and the cartridge neck (not shown) are clean. Fit the
new O-rings (2 and 3) (Fig. 1 on Page 15) and lightly grease them.
2 Put 2 rods (Ø 2.5 mm) (Fig. 4) into the threads for screws (4) to guide the oil separator into the body (Fig. 4).
3Place the new oil separator unit (1) or cleaned original unit (dependent on kit purchased) into the body. Push the
unit down until it is correctly seated.
4 Fit and tighten screws (4) to a torque of 2.5 Nm.
5 Lightly lubricate the gasket at the base of the cartridge (6) with grease.
6 Lubricate new O-ring (5) with grease.
7 Fit O-ring (5) over the cartridge retaining thread.
8 Screw desiccant cartridge (6) up to stop.
9 Fully tighten desiccant cartridge (6) by turning a further ½ turn using a suitable strap wrench.
10 Refit (if necessary) the air processing unit to vehicle and check according to chapter 3.10.
11 Charge the air system to just below cut-out pressure and check the desiccant cartridge for leakage.
Removing the oil separator
Step Service task
1 Clean the outside of the air processing unit and its surroundings to prevent entry of dirt.
2 Secure the ZB44.. either to a simple fixture or using the mounting bolts/studs to make it stable.
3 Unscrew desiccant cartridge (6) counter-clockwise, using suitable strap wrench.
4 Remove the screws (4) and O-ring (5).
5 Fit a suitable pulling tool (7) into oil separator unit (Fig. 3). For detailed specification and correct fitting of
recommended tool see page 16.
6 Pull out the oil separator unit (1) by using of pulling tool (7).
7If the oil separator unit (1) is not being replaced (depending on kit purchased), clean the the original unit (1) with
water using a high pressure hose or alternatively with gasoline. Also clean the housing using a soft cloth.
Service Steps
1
4
5
6
1
1
7

min.50
10-60
3
max.3º
2,8
6,5
59
90º
R1
R3
5
15º
16
3
Service Instructions
Recommended pulling tool for Oil Separator Unit disassembly
Components of pulling tool
Correct fitting of pulling tool
Dimensions of thrust plate Dimensions of pulling tool legs
Holder with
threaded bolt
Adjustable
pulling arms
Thrust plate for
threaded bolt
Ø35
90º
Ø3
Ø20
10
5
6 3

1
2
3
4
5
6
7
(S)
8
9
(S) For devices with steel
covers use the original cover,
clean and replace.
17
3
Service Instructions
3.6 Disassembling and Assembling the Purge Valve (E)
Service kit parts list
Item Kit Description Qty
1 Air Processing Unit (APU) housing 1
2•Retaining ring Ø 27,2 x 1,2 1
3•O-ring Ø 24 x 1,5 1
4•Exhaust piston assembly 1
5•Compression spring 1
6•O-ring Ø 25,12 x 1,78 1
7•End cover 3 or 2
8•Retaining ring Ø 30 x 1,2 1
9•Assembly grease 2 g 1
For Service Kit Part Number see
www.knorr-bremseCVS.com
• Included in kit
Note that component numbering may not correspond to that
shown on separate Service Kit leaflets.
4.1
4.3
4.2

18
3
Service Instructions
Step Service task
1 Lubricate the purge valve bore of the APU housing unit (1) with grease (9).
2Lubricate new O-ring (4.2) and new sealing ring (4.3) with grease (9) and fit onto new piston (4.1). Note: Make sure
O-ring and sealing ring are correctly fitted to piston (4.1).
3 Place assembled exhaust piston assembly (4) into APU housing unit (1).
4 Place new compression spring (5) centrally onto exhaust piston assembly (4).
5Select required new cover (7 or ‘S’) in accordance to ZB44.. type (see removal steps), lubricate new O-ring (6 or 3)
with grease (9) and fit into groove on selected cover (7 or ‘S’).
6 Push assembled cover (7 or ‘S’) into APU housing unit (1).
7
Press down and hold cover (7 or ‘S’) against compression spring (5) and fit retaining ring (8 or 2) securely into groove of the
APU housing unit (1) using suitable tool e.g. circlip pliers.
Fitting the new purge valve
Step Service task - Read and understand all steps before commencing work!
1 Clean the outside of the APU and its surroundings to prevent entry of dirt.
2Position APU so that the purge valve points vertically upwards. Secure in a way to prevent movement but allow for
easy access to the required part.
3
Remove retaining ring (8 or 2) using suitable tool e.g. circlip pliers, whilst holding cover (7 or ‘S’) against
compression spring (5).
4Check type of cover fitted ( 7 or ‘S’ as shown in above diagram) and carefully remove. Then remove compression
spring (5) and piston assembly (4) (see Fig.2).
5 Clean the purge valve bore of APU housing unit (1) with a soft cloth.
Removing the old purge valve
Service Steps
Procedure with the Air Processing Unit (APU) removed from the vehicle (for removal see section 3.4)

3
1
2456
19
3
Service Instructions
Disassembling
Step Service task
1 Remove the rubber protective cap (6).
2 Screw-out the threaded connector (5) with sealing ring (3).
3 Remove the valve tappet (2) (along with O-ring (4)) if it has not come out with the threaded connector (5).
4 Remove the compression spring (1).
5 Clean the tyre inflator housing in the body.
Assembling
Step Service task
1 Place the new compression spring (1) into the tyre inflator housing.
2 Lubricate new O-ring (4) with grease and fit into the groove in the valve tappet (2).
3 Lubricate the new assembled valve tappet (2) with grease.
4 Place the assembled valve tappet (2) into the new threaded connector (5).
5 Fit the new (metallic) sealing ring (3) to the threaded connector (5) and screw-in.
6 Tighten the threaded connector (5) to a torque of 50 Nm
7 Check operation by pushing valve tappet (2) twice.
8 Fit the new rubber protective cap (6) .
9 Refit (if necessary) the air processing unit to vehicle and check according to chapter 3.10.
10 Charge the air system to just below cut-out pressure and check the new tyre inflator for leakage.
Item Description Qty
1 Compression spring 1
2 Valve tappet 1
3 Sealing ring 1
4 O-ring (7 x 1,5) 1
5 Threaded connector 1
6 Protective cap 1
Part Identification
3.7 Disassembling and Assembling the Tyre Inflator (F)
Service Steps
For Service Kit Part Number see
www.knorr-bremseCVS.com
Note that component numbering may not correspond to that
shown on separate Service Kit leaflets.

1
2
3
20
3
Service Instructions
3.8 Replacement of the Double Pressure Sensor (H)
Step Service task
Removal of the double pressure sensor.
1 Remove the two screws (2).
2 Remove the double pressure sensor (3) and the two O-rings (1).
3 Carefully clean the O-ring sealing surfaces.
Replacement of the double pressure sensor
1 Lubricate the two new O-rings (1) and place them into the body.
2 Push the new double pressure sensor (3) into the body and firmly hold in place against the O-rings (1) until the
new screws (2) are fitted and fully tightened to a torque of 6 Nm.
3 Refit (if necessary) the air processing unit to vehicle and check according to chapter 3.10.
4 Prior to returning the vehicle to service, check the new double pressure sensor for function and electrical
connection: during charging the air system, check the pressure signal on the dashboard.
Service Steps
Part Identification
Item Description Qty
1 O-ring 2
2 Screw 2
3 Double pressure sensor assembly 1
For Service Kit Part Number see
www.knorr-bremseCVS.com
Note that component numbering may not correspond to that
shown on separate Service Kit leaflets.