Hitachi RAS-10HRNM, Service Manual, Page: 63 / 482

3.2.4 Brazing work
The most important work in the refrigerant piping installation work is the brazing of the pipes. If it accidentally occurs a
leakage due to a careless brazing process, it will cause clogged capillary pipes or serious compressor failure.
In order to guarantee a proper brazing neck between different pipes surfaces, accurate pipe dimensions after the expansion
process (see the table below):
It is important to control the clearance of the pipe fitting portion as shown below. In the case that a cooper tube expansion
jig is used, following dimensions should be secured.
Copper pipe size Ød1 Gap a Copper pipe size Ød1 Gap a
Ø6.35
+0.08
Ø6.5
+0.1 0.33
6 Ø22.22
+0.09
Ø22.42
+0.1 0.39
10
-0.08 0 0.07 -0.09 0 0.11
Ø9.53
+0.08
Ø9.7
+0.1 0.35
8 Ø25.4
+0.12
Ø25.6
+0.1 0.42
12
-0.08 0 0.09 -0.12 0 0.08
Ø12.7
+0.08
Ø12.9
+0.1 0.38
8 Ø28.58
+0.12
Ø28.78
+0.1 0.42
12
-0.08 0 0.19 -0.12 0 0.08
Ø15.88
+0.09
Ø16.1
+0.1 0.41
8 Ø31.75
+0.12
Ø32.0
+0.1 0.47
12
-0.09 0 0.13 -0.12 0 0.13
Ø19.05
+0.09
Ø19.3
+0.1 0.44
10 Ø38.1
+0.12
Ø38.3
+0.1 0.52
14
-0.09 0 0.16 -0.12 0 0.18
A basic brazing method is shown below.
1. Pre-heat the outer tube for better flowing of the filler metal.
2. Heat inner side tube evenly.
3. Rubber plug.
4. Packless valve.
5. High pressure hose.
6. 0.03 to 0.05 MPa (0.3 to 0.5 Kg/cm
2
G).
7. Reducer valve: open this valve only when the gas is needed.
8. Nitrogen gas flow 0.05 m
3
/h or smaller.
C A U T I O N
• Use nitrogen gas for blowing during pipe brazing. If oxygen, acetylene or fluorocarbon gas is used, it will cause
an explosion or poisonous gas.
• During the brazing work, a lot of oxidation film will be generated inside of the pipes if no oxygen-free nitrogen
gas is blown through the pipes. This film will be flecked off after operation and will circulate in the refrigeration
cycle, resulting in clogged expansion valves, etc. This could origin problems in the compressor.
• Use a reducer valve when nitrogen gas blowing is performed during brazing. The gas pressure should be
maintained within 0.03 to 0.05 MPa. If an excessively high pressure is applied to a pipe, it could origin an
explosion.
3 Piping work and
refrigerant charge
55
SMGB0060 rev. 1- 12/2010
3