ENGINEERING INFORMATION - ASCO Numatics

00484GB-2006/R01
Availability, design and specifi cations are subject to change without notice. All rights reserved.
ENGINEERING INFORMATION
Pressures, fl ow coeffi cients and calculation of fl ow
PRESSURES
. Maximum allowable pressure (MAP) : The maximum allowable pressure (MAP) in pipework is the maximum effective pressure (in bar or in Pa)
which can be applied to the pipework in a given system (1 bar = 10 2 kPa)
. Inlet (or upstream) pressure : fl uid pressure at the entrance to the pneumatic component
. Outlet (or downstream) pressure : fl uid pressure at the exit from the pneumatic component
. Differential pressure Δ P : difference in pressure between the inlet (upstream) pressure and the outlet (downstream) pressure.
FLOW COEFFICIENTS
. Kv (following standard NF E 29312) :
The French KV value is an experimental coeffi cient based on laboratory conditions and expresses the volumetric fl ow across a valve. The KV
coeffi cient is defi ned as the fl ow of water through a fully open valve in litres per minute with a pressure differential ΔP of 1 bar.
. Cv : The imperial equivalent of the KV coeffi cient is the Cv coeffi cient defi ned as the fl ow of water through a valve in US gallon per minute at a
differential pressure ΔP of 1 psi across the valve.
Cv and Kv can be converted as follows : Kv = 14,3 Cv and Cv = 0,07 Kv
. C and b (following standard ISO 6358) :
Coeffi cients C (sonic conductance) and b (critical pressure ratio) following standard ISO 6358 allow fl ow calculation under sonic conditions
(See spool valves 541 - 543 - sections E and F).
C =
C =
q* m
ρ p ο in
q* v
pin q* : mass fl ow rate q* (kg/s) or volume q* (m m v 3 /s) through a component at sonic fl ow
p : inlet pressure (bar)
in
ρ ο = 1,3 kg/m 3 : density under standard conditions (p 0 = 1 bar, T 0 = 293,15 K and 65% relative humidity)
b : pressure ratio below which the fl ow is sonic:
q m
q* m
b =
Pout Pin depending on P in , T 1
and C
P : outlet pressure (bar)
out
P : inlet pressure (bar)
in
0 b 1
Sonic fl ow Subsonic fl ow
CALCULATION OF FLOW (for air and gas)
. Defi ning fl ow at 6 bar :
The corresponding leafl ets give for each product its mean fl ow in litres per minute at 6 bar at a standard reference atmosphere (ANR) conforming
to ISO 8778 (with Δ P = 1 bar)
. Calculation of fl ow :
Δ P < P inlet /2
Q = 28,16 x Kv x ΔP x P in
including correction for temperature and density
Q = 475 x Kv x (ΔP x P in )
(T a x d)
Q = Flow in l/min
ΔP = Differential pressure, in bar
. Flow graphs : (see following page).
P in and T 1 are constant
Ellipse quarter, depending on P in , T 1
and C and b coeffi cients
P out / P in
Δ P ≥ P inlet /2
(Maximum allowable fl ow)
Q = 14 x Kv x P out
P in = Absolute inlet pressure, in bar
P out = Absolute outlet pressure, in bar
T1, temperature (°K) measured when the fl ow is sonic
including correction for temperature and density
Q = 238,33 x Kv x P x 1
out
(T x d) a
T a = Absolute temperature, in Celsius degrees
d = Density compared with air
All leafl ets are available on: www.asconumatics.eu
P045-1
A

All leafl ets are available on: www.asconumatics.eu
P045-2
Flow graphs - ENGINEERING INFORMATION
HOW TO USE THE GRAPHS
Depending on the supply pressure, use the appropriate graph: either 0 - 2 bar or 0 - 40 bar.
The graph shows the relationship between the fl ow and the pressure drop Δp, depending upon the upstream pressure and the fl ow
coeffi cient (Kv in litres per minute).
Δp3
KV 132
P amont : 8 bar 950
Upstream P : 8 bar
AIR PRESSURE 0 to 2 bar
Δp
Example : Find the fl ow of a valve Ø 25 mm, KV = 132, under the following conditions :
– upstream gauge pressure : 8 bar
– pressure drop Δp : 3 bar
Proceed as shown in the diagram to fi nd a fl ow = 950 m3 /h.
If the pressure drop exceeds the values shown in the graph, the fl ow is identical to that with "critical
pressure drop", so that :
Δp = absolute downstream pressure = absolute upstream pressure
2
1
0,5
0,1
0,05
0,01
0,005
0,001
KV
1
1
0,5
5
10
10
5
50
100
50
100
500
1 000
5 000
10 000
50 000
0 0,5 1
P : Upstream gauge pressure in bar
15 0,1 0,5 1
0,1
5 10
1
100 1 000 10 000 100 000 m3/h (ANR)✻
Q :Flow
10 100 1 000 10 000 I/s (ANR)✻
✻ ANR : Standard reference atmosphere
AIR PRESSURE 0 to 40 bar
1
0,5
Δp
0,1
0,05
0,01
KV
0 1 2 3 4 5 678910
20 30 40 1 10
P : Upstream gauge pressure in bar
5
10
✻ ANR : Standard reference atmosphere
500
1 000
5 000
10 000
0,1 1 10 100 1 000 10 000
50 000
100 000
100 000
100 1 000 10 000 100 000
500 000
100 000
m3/h (ANR)✻
Q :Flow
I/s (ANR)✻
00484GB-2006/R01
Availability, design and specifi cations are subject to change without notice. All rights reserved.