User Manual

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Siemens Control device PN25, safety function to DIN EN 14597 CE1N4389en
Building Technologies 10.01.2011
Absolute working pressure [bar]
Medium temperature [°C]
wet steam avoid
saturated steam
superheated steam
permissible range of use
For saturated steam and superheated steam the differential pressure Δp
max
across
the valve should be close to the critical pressure ratio.
Pressure ratio =
%100
p
pp
1
31
⋅
−
p
1
= absolute pressure before valve in kPa
p
3
= absolute pressure after valve in kPa
Subcritical range Supercritical range
%42%100
p
pp
1
31
<⋅
−
%42%100
P
pp
1
31
≥⋅
−
Pressure ratio < 42% subcritical Pressure ratio ≥ 42% supercritical
(not recommended)
k
)pp(p
m
4.4k
313
vs
⋅
−⋅
⋅=

k
p
m
8.8k
1
vs
⋅⋅=

m

= steam quantity in kg/h
k = factor for superheating of steam = 1 + 0.0012 · ΔT (k = 1 for saturated steam)
ΔT = temperature differential in K between saturated steam and superheated steam
Example
given saturated steam 151.8 °C
p
1
= 500 kPa (5 bar)
m

= 460 kg/h
pressure ratio = 30 %
saturated steam 151.8 °C
p
1
= 500 kPa (5 bar)
m

= 460 kg/h
pressure ratio = 42 %
(supercritical permitted)
required k
vs
, valve type k
vs
, valve type
procedure
100
p30
pp
1
13
⋅
−=
)bar5.3(kPa350
100
50030
500p
3
=
⋅
−=
h/m83.81
)350500(350
460
4.4k
3
vs
=⋅
−⋅
⋅=
h/m09.81
500
460
8.8k
3
vs
=⋅⋅=
selected k
vs
= 10 m
3
/h  MKB532.25-10G k
vs
= 8 m
3
/h  MKB532.25-8G
Working pressure
and medium tem-
perature
Saturated steam
Superheated steam
Recommendation
Calculation of the k
vs
value for steam