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CALCULATIONS
General
The maximum allowable leak--rate (according the EN676 and
EN746--2) is 0,1 % of the maximum burner capacity. The test
time necessary to detect a falling valve is a function of:
−
inlet pressure
−
test volume
−
burner capacity.
When the volume between two safety--valves is bigger it
takes more time (in case of a leaking valve) to change the
status of the gas pressure switch. The correct OS--number
for the A4021A can be selected after calculating the
appropriate test--times for the intended application.
The switching point of the pressure--switch is set to 50 % of
the maximum inlet pressure.
The test period Tp is calculated from the inlet pressure Pi, the
test volume Vp ( see Table 4.) and maximum burner capacity
Qm, in formula:
2 x Pi x Vp
Tp ≡
Qm
Pi =
inlet pressure [mbar]
Vp =
test volume [ dm
Qm =
burner capacity [dm
3
Table 4. Volumes in dm
pipe L (including V1 and V2)
DN
Length between valves (m)
0
0,5
10T
0.06
0.10
15T
0.06
0.15
20T
0.12
0.28
25T
0.19
0.44
32T
0.69
1.1
40T
0.71
1.4
50T
1.3
2.3
65T
2.7
4.4
80T
2.9
5.4
65F
3.2
4.9
80F
4.4
6.9
100F
6.5
10.5
NOTE:
T = Thread
F = Flange
V
= volume of 2 valves with L= 0 m
0m
IMPORTANT
The total volume Vp has to be calculated with all
volumes between the tested valves: internal
volumes of valves and all pipes
Calculation examples
Example 1
[ s ]
3
], see also Table 4.
3
/h]
for UGV valves Vp with length of
1
1,5
2
0.14
0.18
0.22
0.24
0.33
0.42
0.43
0.59
0.74
0.68
0.93
1.2
1.5
1.9
2.3
2.0
2.7
3.3
3.3
4.2
5.2
6.0
7.7
9.3
7.9
10
13
7.5
8.2
9.8
9.4
12
14
14.4
18
22
Calculate the maximum pipe length between two 1 1/2" safety
valves when an A4021A valve proving system is used with a
test period (per valve) of 25 seconds.
Given:
Pi = 75 mbar
Qm = 30 dm
valve: 1 1/2"→DN40
To be calculated: L(max.) [m]
Calculation:
2 x Pi x Vp
Tp ≡
Qm
25 x 30
Vp ≡
2 x 75
From Table 4. :
DN40T, Vp= 5 dm
Example 2
Calculate the test period (per valve) in a given situation.
Given:
Pi = 150 mbar
Qm = 60 dm
valve: VE4065A with 0.5 meter pipe
To be calculated: Tp [s]
Calculation:
per
From Table 4. :
extra
DN65T, L=0.5m
meter
2 x Pi x Vp
0.08
Tp ≡
0.18
Qm
0.31
Choose always a A40121 with a test time (per valve) higher
0.49
than the (minimum) calculated test time Tp.
0.80
Example 3
1.3
2.0
3.3
5
3.3
5.0
7.9
Calculate the test period (per valve) in given situation.
Given:
Pi = 150 mbar
Qm = 100 dm
valve: VE4080A with 1 meter pipe (L1)
pilot valve: VE4025 with 0.5 meter pipe (L2)
To be calculated: Tp [s]
Calculation:
From Table 4. :
DN80T, L1=1m
DN25T, L2=0.5
Vp = V
1m + (
2 x Pi x Vp
Tp ≡
Qm
Choose always a A40121 with a test time (per valve) higher
than the (minimum) calculated test time Tp.
11
3
/h
Tp x Qm
[ s ] → Vp ≡
2 x Pi
3
= 5
[dm
]
3 →
length L = 2 + (5--3.3)/1.3 = 3.3 m.
3
/h
→
Vp = V
4.4 dm
0.5m =
2 x 150 x 4.4
[ s ] → Tp ≡
60
3
/h
V
V
7.9 + (0.44 -- 0.19/2) = 8.25 dm
0.5m --
0m =
2 x 150 x 8.25
[ s ] → Tp ≡
100
3
[dm
]
3
.
= 22[ s ]
3
.
= 25 [ s ]
EN2R--9023 9705R0--NE
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