Compact

Type 459 HDD
Determination of coefficent 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 )
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
d 0 Ø 6 mm
K dr = α w = f (h/d 0 ) – S/G
0,85
d 0 Ø 9 mm
K dr = α w = f (h/d 0 ) – S/G
0,80
d 0 Ø 13 mm
K dr = α w = f (h/d 0 ) – L
0,75
0,70
A lift restriction
ist not applicable
because the actual
design and the certified
lift ≤ 1,5 mm / 1 / 16 inch.
Coefficient of discharge K dr / αw
0,65
0,60
0,55
0,50
0,45
0,40
0,35
0,30
0,25
0,15
0,20
0,05 0,1 0,15 0,2
0,25
0,05 0,1 0,15
Ratio of lift / flow diameter h / d 0 0,23
Ratio of lift / flow diameter h / d 0
Coefficient of discharge K dr / αw
0,2
0,22
0,25
d 0 Ø 6 mm
d 0 Ø 9 mm
d 0 Ø 13 mm
K dr = α w = f (h/d 0 ) – S/G
0,65
K dr = α w = f (h/d 0 ) – L
0,55
K dr = α w = f (h/d 0 ) – L
0,60
0,50
Type 459 HDD
A lift restriction
ist not applicable
because the actual
design and the certified
lift ≤ 1,5 mm / 1 / 16 inch.
Coefficient of discharge K dr / αw
Ratio of lift / flow diameter h / d 0 0,22
Ratio of lift / flow diameter h / d 0
0,45
0,55
0,40
0,50
0,35
0,45
0,30
0,40
0,25
0,35
0,20
0,30
0,15
0,10
0,15
0,20
0,25
0,05 0,1 0,15
Coefficient of discharge K dr / αw
0,2
0,23
0,25
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 )
d 0 Ø 6 mm
d 0 Ø 9 mm
d 0 Ø 13 mm
K dr = α w = f (p a0 /p 0 ) und K b = f (p a0 /p 0 )
0,9
K dr = α w = f (p a0 /p 0 ) and K b = f (p a0 /p 0 )
0,9
K dr = α w = f (p a0 /p 0 ) and K b = f (p a0 /p 0 )
1,10
The certified coefficent
of discharge K dr / α w
S/G = 0,81
L = 0,70
is constant in
set pressure range.
How to use please refer to page 00/08
Coefficient of discharge K dr / αw
0,8
0,8
1,00
Ratio of back pressure / set pressure p a0 / p 0 Ratio of back pressure / set pressure p a0 / p 0
0,90
0,7
0,7
0,80
0,6
0,6
0,70
0,5
0,60
0,5
0,4
0,50
0,4
0,40
0,3
0,3
0,30
0,2
0,2
0,20
0,1
0,10
0,1
0,0
0,00
0,0
0,2 0,25 0,3 0,35 0,4 0,45
0,2 0,3 0,4 0,5 0,6 0,7 0,8
Back pressure correction factor K b
Coefficient of discharge K dr / αw
0,9
0,909
1,00
0,90
0,80
0,70
0,60
0,50
0,40
0,30
0,20
0,10
0,00
Back pressure correction factor K b
06/18 LWN 481.01-E