Hitachi RAS-4-HNCE - Brazing Work

3. Piping work and refrigerant charge
55
SMGB0079 rev.0 - 01/2013
3
3.1.4 Brazing work
The most important work in the refrigerant piping installation work is the brazing of the pipes. If it accidentally occurs a leak-
age 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 expan-
sion process (see the table below):
It is important to control the clearance of the pipe tting 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
Ø9.52
+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 owing of the ller 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 ow 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uorocarbongasis used, it will
causeanexplosionorpoisonousgas.
• Duringthebrazingwork,alotofoxidationlmwillbegeneratedinsideofthepipesifnooxygen-freenitrogen
gasisblownthroughthepipes.Thislmwillbeecked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main-
tainedwithin0.03to0.05MPa.Ifanexcessivelyhighpressureisappliedtoapipe,itcouldoriginanexplosion.