8.2.1 Basic principles
• Polyamide (PA) tubes must in all circumstances: - be kept away from heat sources
- be laid in such a way that no abrasion can occur - be free from trapped stresses
- be laid without kinking..
• Only PA tubing in accordance with MAN standard M 3230 Part 1 is to be used ( www.normen.man- nutzfahrzeuge.de(http://www.normen.man-nutzfahrzeuge.de), registration required. In accordance with the standard this tubing is marked with a number starting with ‘M 3230’ every 350 mm.
• Remove lines to protect them before welding work takes place.
• For welding work, see also the Chapter „Modifying the chassis“ – „Welding the frame“ section.
• In view of the risk of heat build-up, PA pipes must not be attached to metal pipes or holders that are connected to the following assemblies: - Engine - Air compressor - Heating - Radiator - Hydraulic system.
8.2.2 Voss 232 system plug connectors
For brake/air lines, only Voss 232 (MAN standard: M 3298) and Voss 230 system plug connectors (for NG6 smaller diameter pipes and special connectors such as the double mandrel; MAN standard: M 3061) are permitted ( www.normen.man-
nutzfahrzeuge.de(http://www.normen.man-nutzfahrzeuge.de), registration required). The standard referred to contains detailed instructions that must be applied in all cases when installing pneumatic lines and assemblies. Body manufacturers can obtain the MAN standards listed here from
www.normen.man-nutzfahrzeuge.de(http://www.normen.man-nutzfahrzeuge.de) (registration required).
The system has two detent stages. If the plug element has only been inserted as far as the first detent, the System 232 connection leaks deliberately; incorrect plug element engagement can be identified immediately by the noise that occurs.
• The system must be relieved of pressure before the union screw is slackened.
• After the connection between plug element and union screw has been separated the union screw must be renewed, since the retaining element is rendered unfit
for further use when it is unscrewed.
• The union screw must therefore be slackened off when a line is detached from an assembly. The plastic pipe with plug element, union screw
and retaining element constitutes a re-usable unit. Only the O-ring that seals the thread (see Fig. 99) has to be renewed. (Grease the O-ring and clean the union screw when installing).
• The plug connection unit described above is to be screwed into the assembly hand-tight, then finally tightened to 12 ± 2 Nm (in metal) or 10 ± 1 Nm (in plastic).
8.2.3 Installing and attaching lines Basics of installing lines:
• Lines must not be laid loose; existing means of attachment and/or conduits are to be used. • Do not heat plastic pipes when installing them, even if they are to follow a curved path. • When attaching pipes, make sure that the PA pipes cannot become twisted.
• Install a pipe clip or, in the case of a cluster of pipes, a cable tie at the beginning and end in each case.
• Corrugated wiring harness pipes are to be attached to plastic consoles in the frame or, in the engine area, to prepared cable routes using cable ties or clips.
• Never attach more than one line to the same hose clip.
• Only PA pipes (PA = polyamide) designed to DIN 74324 Part 1 or MAN Standard M 3230 Part 1 (extension of DIN 74324 Part 1) may be used
( www.normen.man-nutzfahrzeuge.de(http://www.normen.man-nutzfahrzeuge.de), registration required).
• Add 1% to the length of the PA pipe (corresponding to 10 mm for each metre of cable), because plastic pipes contract in the cold and the vehicles must be capable
of working at temperatures down to - 40°C.
• The pipes must not be heated when being installed.
• When cutting plastic pipes to length, use plastic pipe cutters; sawing them to length creates ridges on the cut faces and chippings get into the pipe.
• PA pipes may rest on the edges of the frame or in the frame openings. A minimal amount of flattening at the points of contact is tolerated (maximum depth of 0.3 mm). However, notched abrasion is not permitted.
• PA pipes are allowed to come into contact with each other. There should be minimal flattening at the points where the pipes come into contact with each other.
• PA pipes can be bundled together with a cable tie but must be positioned parallel to each other (they should not cross over each other). PA pipes and
corrugated pipes should only be bundled together with pipes of the same type.
The restriction in movement caused by the pipes becoming stiffer when bundled together should be taken into account.
• Covering the edges of the frame with a cut corrugated pipe will cause damage; the PA pipe will be worn at the point where it comes into contact with the
corrugated pipe.
• Points of contact with the edges of the frame can be protected with a protective spiral (see Fig. 100).
The protective spiral must tightly and completely grip the pipe it is protecting. Exception: PA pipes Ø ≤ 6 mm). Fig. 100: Protective spiral on a PA pipe ESC-151
• PA pipes/PA corrugated pipes must not come into contact with aluminium alloys, e.g. aluminium tank, fuel filter housing; aluminium alloys are subject
to mechanical wear (fire risk).
• Pipes that cross over and pulsate (e.g. fuel pipes) must not be joined together with a cable tie at the cross-over point (risk of chafing). • No cables/pipes should be fixed rigidly to injection pipes and steel fuel feed pipes for the flame starting system (fire risk, risk of chafing). • Accompanying central lubricating cables and ABS sensor cables may be attached to air hoses only if a rubber spacer is fitted.
• Nothing may be attached to coolant hoses and hydraulic hoses (e.g. steering hoses) by means of cable ties (risk of chafing).
• Under no circumstances should starter cables be bundled together with fuel or oil pipes; this is because it is essential that the cable from the positive terminal
does not chafe.
(minimum distance from
heat shields ≥ 100 mm, from the exhaust ≥ 200 mm)
• Metal pipes are pre-strengthened and must not be bent or installed in such a way that they bend during operation.
If assemblies/components are mounted in such a way that they can move with respect to each other, then the following basic rules must be followed when routing cables/pipes:
• The cable/pipe must be able to follow the movement of the assembly without any problem; ensure that there is sufficient distance between the moving parts for
this (rebound/compression, steering angle, tilting of cab). The cables must not be stretched.
• The respective starting and end point of the movement is to be defined exactly and used as the fixed clamping point.
The PA or corrugated pipe is gripped tightly at the clamping point using the widest cable tie possible or a clip suitable for the diameter of the pipe.
• If PA and corrugated pipes are laid at the same junction, the stiffer PA pipe is laid first. The softer corrugated pipe is then attached to the PA pipe.
• If a pipe is to tolerate movements at right angles to the direction in which it is laid, then sufficient distance between the clamping points must be guaranteed
(rule of thumb: distance between clamping points ≥ 5 x the amplitude of movement to be withstood).
• Large amplitudes of movement are best withstood by laying the pipe in a U-shape and by permitting movement along the arms of the „U“. Rule of thumb for the minimum length of the slack loop:
Minimum length of the slack loop = 1/2 · amplitude of movement · minimum radius · π
• The following minimum radii are to be observed for PA pipes (the respective start and end point of the movement is to be defined precisely as the fixed
clamping point):
Table 25: Minimum bending radii for PA pipes
Nominal pipe diameter - Ø [
mm ] 4 6 9 12 14 16
Bending radius r [ mm ] 20 30 40 60 80 95
Table 26: Maximum space between clips used to secure pipes in relation to pipe size
Pipe size 4x1 6x1 8x1 9x1,5 11x1,5 12x1,5 14x2 14x2,5 16x2
Clip spacing [mm] 500 500 600 600 700 700 800 800 800
8.2.4 Compressed air loss
Compressed air systems cannot achieve 100% efficiency and slight leakage is often unavoidable despite the most careful installation work. The question is therefore what degree of air pressure loss is unavoidable and when does the loss become too high? Simply put, any loss of air pressure that would render a vehicle undriveable once the engine is started after a period of 12 hours parked must be regarded as unacceptable. Based on this requirement there are two different methods of determining whether air loss is unavoidable or not:
• Within 12 hours of the system having been charged to its cut-off pressure, the pressure must not be below < 6 bar in any circuit. The check must be made
with depressurised spring-loaded brake release units, in other words with the parking brake applied.
• The pressure in the tested circuit must not have fallen by more than 2% within ten minutes of charging the system to its cut-off pressure. If air loss is greater than described above, an unacceptable leak is present and must be eliminated.
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