Compact

How to use
General
Sample Determination of K dr /α w : Type 459, d 0 13 mm
Type 459
Determination of coefficient of discharge
in case of lift restriction or back pressure
Diagram for evaluation of ratio of lift /flow diameter (h/d 0 )
in reference to the coefficient of discharge (K dr /α w )
1
0,85
d 0 Ø 13 mm
K dr = α w = f (h/d 0) – S/G
h = Lift [mm]
d 0 = Flow diameter [mm] of selected safety
valve, refer to table article numbers
h/d 0 = Ratio of lift / flow diameter
p a0 = Back pressure [bar a]
p 0 = Set pressure [bar a]
p a0/p 0 = Ratio of back pressure / set pressure
K dr = Coefficient of discharge
acc. to DIN EN ISO 4126-1
α w = Coefficient of discharge
acc. to AD 2000-Merkblatt A2
K b = Back pressure correction factor
acc. to API 520 topic 3.3
1a
0,60
0,75
0,65
0,55
Coefficient of discharge K dr / αw
0,45
0,35
0,25
0,15
0,05
0,1 0,15
0,2
0,25
Ratio of lift / flow diameter h / d 0
0,175 1b
Diagram for evaluation of ratio of the coefficient of discharge (K dr /α w )
in reference to the ratio of back pressure/set pressure (p a0 /p 0 )
0,23
2
0,9
d 0 Ø 13 mm
K dr = α w = f (p a0 /p 0 ) and K b = f (p a0 /p 0 )
1,10
2b
0,79
0,8
0,7
1,00
0,90
0,80
0,97
2c
0,6
0,70
Coefficient of discharge K dr / αw
0,5
0,4
0,3
0,2
0,1
0,0
0,2 0,3 0,4 0,5 0,6 0,7 0,8
Ratio of back pressure / set pressure p a0 / p 0
0,30
2a
0,9
0,909
0,60
0,50
0,40
0,30
0,20
0,10
0,00
Back pressure correction factor K b
Explanation
Sample – Type 459, flow diameter d 0 = 13mm, rated lift h = 3,0mm, K dr /α w S/G = 0,81
Diagram 1
Diagram 2
1 2
Determination of the restricted lift due to reduced K dr /α w Determination of reduced K dr /α w or K 1) b due to back pressure
Step Description Sample Step Description Sample
Calculate the required coefficent of discharge of 1a
Calculate the back pressure ratio p a0 /p 0 using the 2a
1 the selected safety valve. Applicable formulas
1 actual values for set pressure p 0 [bar a ] 100
are stated in codes and standards.
K dr /α w = 0,60 and back pressure p a0 [bar a ] 30 p a0 /p 0 = 0,30
2
Select the starting point (0,60) at the Y-axis
of the diagram.
2
Select the starting point (0,30) at the X-axis
of the diagram.
3
Lay a horizontal line onto the ratio graph for
identify the intersection point.
3
Lay a vertical line onto the ratio graph to identify
the intersection point.
4
5
Lay a vertical line to the X-axis to identify the
ratio of lift / flow diameter (h/d 0 ).
Calculate the restricted lift using the formulas
h = d 0 x h/d 0 . (For ordering a lift restriction
please use option code J51 ref. to page 09/16)
1b
Lay a horizontal line to the Y-axis to identify 2b K dr /α w = 0,79
4
h/d the reduced K dr /α w or K b .
0 = 0,175 2c K b = 0,97
h = 13 x 0,175
h = 2,3 mm
5
Calculate the sizing with the established
K dr /α w or K b .
LWN 481.01-E
1)
Back pressure correction factor Kb acc. to API 520 topic 3.3. For further information refer to LESER Engineering Handbook
00/08