Fukuda FL-601 Series, Operational Manual

Page: 21 / 123

20
PRINCIPLE WHAT IS AN AIR LEAK TESTER?
□
The Relationship Between the Indication and the Leak Rate
Equation to calculate the leak rate:
Definitions of the symbols used in the equation are shown below:
△
V
L
：
Leak rate
（
ml/sec
）
Ｔ ：
Detection time
（
sec
）
△
P
：
Differential pressure rate generated in detection time T
（
Pa or
㎜
H
2
0
）
Po
：
Atmospheric pressure
（
101325Pa or 1.033
×
10
4
㎜
H
2
0
）
V
Ｗ
：
Work side internal volume
（
ml
）
V
Ｓ
：
Master side internal volume
（
ml
）
k
：
Sensor coefficient
（
0.4 x 10
-5
ml/Pa or 0.4
×
10
- ４
ml/
㎜
H
2
0
）
P
T
：
Test pressure (gauge)
（
Pa or kg/cm
2
G
＝×
10
4
㎜
H
2
0
）
【
Reference
】
Pressure units and conversion chart
1Pa 1MPa 1mmHg 1km/cm
2
1mmH
2
O
1Pa 1 1 ×10
-6
7.500 62×10
-3
1.019 72×10
-5
1.019 72×10
-1
1MPa 1×10
6
1 7.500 62×10
3
1.019 72×10
-1
1.019 72×10
5
1mmHg 1.333 22×10
2
1.333 22×10
-4
1 1.359 91×10
-3
1.359 51×10
1
1kg/cm 2 9.806 65×10 4 9.806 65×10 -2 7.355 59×10 2 1 1 ×10 4
1mmH
2
O 9.906 65 9.806 65×10
-6
7.355 59×10
-2
1×10
-4
1
In general, the leak tester will not display the
leak rate during the detection process.
The indicated value is the pressure alteration
rate (often called delta P), which is the rate of
the resultant pressure decay, equal to the
leak rate.
This concept can be easily explained by
portraying water leaking from buckets.
Compare two buckets full of water, with one
bucket leaking. The difference of the level of
the bucket which is not leaking (the
standard) and that of the bucket being
evaluated is indicated on the leak tester.
From this, one can calculate the amount
which had leaked. In order to get the proper
leak rate output from the air leak tester, we
need to convert this value.
Indication
during
Detection
Te
st
Pressu
re
Indi
cation
Minute volume
change with
pressure change.
Leak
Rate
Differential
Pressure Sensor
( )
⎪⎭
⎪
⎬
⎫
⎪⎩
⎪
⎨
⎧
+
⎜
⎜
⎝
⎛
⎟⎟
⎠
⎞
+ +
⋅
Δ
= Δ
T 0
S
W
W
0
L
P P
V
V
1 k V
P T
P
V