Catalog - Tri-State Technical Sales Corp.

SIZING: GASES AND LIQUIDS
16
REF: API RP 520, Part 1
Gases
To size for gases, use the formulas below.
To select the proper orifice for the particular service
conditions, the following information is required:
1. Required flow capacity
2. Required set pressure
3. Operating Pressure – to assure that it is below
the reseat pressure
4. Overpressure (10% Maximum)
5. Molecular Weight/Gas Constant of Media
6. Process Temperature
Gases or Vapors
(US units)
A =
V
MTZ
6.32 CKK b
K c
P 1
- OR - - OR -
A = W
2
TZ
131.6W
A = Required Valve Orifice Area (in 2 or cm )
A
CKK b
K c
P TZ
1 M
CKK b
K c
P 1 M
Q = Required Flow Rate (gpm or lpm)
G = Specific Gravity of Liquid
A = Required Valve Orifice Area (in 2 2
or cm )
K = Certified (Derated) Coefficient of Discharge
3
V = Required Flow Capacity (scfm or Nm /min)
(see chart below)
W = Required Flow Capacity (lb/hr or kg/hr)
K c
= 0.9 with rupture disk upstream of relief valve;
= 1.0 with no rupture disk
K = Certified (Derated) Coefficient of Discharge
(see chart below)
K v
= Viscosity Correction Factor (see Page 17)
P 1
= Pressure at Valve Inlet During Flow (psia or kPaa) P 1
= Pressure at Valve Inlet During Flow (psig or kPag)
= Set Pressure + Overpressure + P atm
= Set Pressure + Overpressure
P atm
= Atmospheric Pressure
14.7 psia or 101.3 kPaa if unknown
P 2
= Backpressure (psig or kPag)
C = Gas Constant
M = Molecular Weight of Flowing Media
T = Inlet Temperature, Absolute
R = (F + 460) or K = (C + 273)
DISCHARGE COEFFICIENTS (K)
Z = Compressibility Factor
if Unknown, Z = 1.0
F7000 F8000
K b
= Backpressure Correction Factor -
See page 18 for subcritical flow;
use 1.0 for critical flow
K c
= 0.9 with rupture disk upstream of relief valve;
= 1.0 with no rupture disk
Liquids
To size for liquids, use the formulas below.
To select the proper orifice for the particular service
conditions, the following information is required:
1. Required flow capacity
2. Required set pressure
3. Operating Pressure – to assure that it is below
the reseat pressure
4. Acceptable Overpressure (10% Maximum)
5. Specific Gravity of the Liquid
6. Backpressure
(SI units) (US units) (SI units)
352.5V MTZ
Q G
11.78Q G
A = A = A
CKK =
b
K c
P 1 38 KK c
K v
P 1
- P 2
KK c
K v
P 1
- P 2
Gas .824 .878
*Liquid .634 --
*F300 & F500 modulating pilots only
F7000/8000 SERIES