8. Variables

8. Variables

cvc sonic velocity in the "vena contracta"

DN nominal size

Dipipe pipe inside diameter

d0 circle diameter

f frequency

fpeak peak frequency

Fd valve form factor

FL pressure recovery factor

F(St) frequency distribution function

F1,F2 constants for efficiency definition according to
VDMA 24422 for liquids

FF pvcmin/pv factor for liquids

G1,G2 constants for efficiency definition according to
VDMA 24422 for gases/vapors

Kc incipient cavitation index

kv kv value (flow capacity) in [m³/h]

LpA sound pressure level [dB] at 1m from the valve

LWI internal sound power level [dB] , 10 log
(Pinternal sound / 10-12 Watt)

LWA external sound power level [dB] , 10 log
(Pexternal sound / 10-12 Watt)

Mavc Mach number in the "vena contracta"

Maj Mach number in jet constriction range

MaDN2 Mach number in valve output cross-section

p1 inlet pressure

p2 outlet pressure

pv vapor pressure

pvc pressure in "vena contracta"

pc critical pressure

Pinternal sound internal sound power

Pjet jet power

p0 reference pressure difference 1 bar

RR(f) frequency-dependent pipe transmission loss
(internal sound to external sound power)

Sb seat hole diameter

St Strouhal number

Stp Strouhal number for peak frequency

T1 inlet temperature

uvc velocity in the "vena contracta"

W mass flow

x differential pressure ratio for gases and vapors, x=(p1-p2)/p1

xF differential pressure ratio for liquids, xF=(p1-p2)/(p1-pv)

xFz differential pressure ratio for beginning cavitation (z value)

xT differential pressure ratio for flow limitation

xcr differential pressure ratio for critical flow (gases/vapors)

Y load

DIN IEC 534 expansion factor

z value with Y=75% load

G acoustic energy coefficient for gases/vapors

G VDMA acoustic energy coefficient for gases/vapors according to
VDMA 24422 (1989)

, n density, standard density

density at valve inlet

density at valve outlet

reference density 1000 kg/m³

, correction terms for sound level according to VDMA

adiabatic exponent

friction coefficient [N/mm] dependent on stem seal

coefficient [N/mm] dependent on required sealing class

friction coefficient [N/mm] for pressure balanced plugs

stem diameter

seat hole diameter

travel velocity

sign sign

actuator force

actuator torque

friction forces

inertial forces (force due to weight, force due to acceleration)

spring force

pressure force

bellows force

flow forces

sealing force (seat loading force) when valve closed

signal pressure

lower value: spring range

upper value: spring range

diaphragm surface area, actuator size

spring bias force

H valve position

nominal travel of control valve

spring stiffness

actuator internal volumes (diaphragm chamber, filled with air)

minimum actuator internal volumes (dead volumes)

temperature in actuator internal volumes

Opening times: for valve opening

Closing times: for valve closing

differential pressure ratio for valve accessories

critical differential pressure ratio (flow limitation)

value accessories

mass flow accessories

supply pressure

atmospheric pressure