Compact

Type 439
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
Kdr = α w = f (h/d 0 )
Type 439
A lift restriction ist not applicable
because the actual design and
the certified lift are
≤ 1,5 mm / 1 /16 inch.
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 )
0,5
K dr = α w = f (p a0 /p 0 ) and K b = f (p a0 /p 0 )
1,10
0,4
d 0 10 "S/G"
1,00
0,90
0,80
How to use please refer to page 00/08
Coefficient of discharge K dr / αw
0,3
0,2
0,1
0
0,2 0,3 0,4 0,5 0,6 0,7
Ratio of back pressure / set pressure p a0 / p 0
0,70
0,60
0,50
0,40
0,30
0,20
0,10
0,00
0,8 0,9
0,835
Back pressure correction factor K b
03/16 LWN 481.01-E