VEGA VEGADIF 34 … 51 - Manual (Page 51)

VEGADIF 34 … 51 51
20094-EN-030731
The following must be noted:
- The impulse line from the adjustment pot to
the vessel must be run with a slight gradient
to the vessel; excess condensate returns to
the vessel, the level in the adjustment pot
remains constant.
- Block valve „2“ between vessel and adjust-
ment pot must not impede the steam line to
the adjustment pot; the installation must
prevent water pockets from forming in the
valve.
- If there is insufficient condensate formation
in the adjustment pot, additional liquid must
be added in small quantities via dosing
valve „6“.
- If the reference liquid has a different density
than the condensate column (1.0 g/cm 3 ),
this has to be taken into account for the
span adjustment.
For this installation, a blow down valve and a
separator for impurities are recommended.
This measure is not necessary if the medium
is clean and the formation of buildup or sludge
in the pipelines is not expected.
Note:
For this installation connection, a measuring
cell which allows a lowering of the zero point
down to -100 % (of measuring range) must be
implemented.
Example VEGADIF 45:
Transmitter directly flanged
1)
1 Transmitter
2 Block valve
3 Adjustment pot
4 Separator for impurities
5 Blow down valve
6 Dosing valve
7 Vent or drain valve
2
4
5
7
3
6
1
h
1
h
2
∆ p
h = ––––––
ρ
• g
Installation connections
1 Transmitter
2 Block valve
3 Separator for impurities
4 Blow down valve
5 Emptying valve
This arrangement has the advantage that zero
and span can be checked (modified) without
emptying the vessel. The valves 5 and 6 allow
the necessary venting/emptying of the tap-
ping socket.
Installation on closed vessels with overlaid
steam pressure
In a closed vessel with steam pressure, the
product level is determined via the measure-
ment of the hydrostatic pressure. The sum of
the steam pressure and hydrostatic pressure
acts as total pressure on the bottom of the
vessel. The hydrostatic pressure is therefore
the difference between total pressure and
overlaid steam pressure.
The transmitter receives the total pressure on
the plus side via the isolating diaphragm, the
overlaid pressure on the minus side via the
impulse line and the process fitting. In a sepa-
rate adjustment pot, a fixed level is generated
by existing condensate. This condensate
column transmits the steam pressure to the
minus side of the transmitter and protects the
measuring cell against hot steam.
2
3
4
1
5
Example VEGADIF 45:
Transmitter flange via maintenance unit
h
1
h
2
∆ p
h = ––––––
ρ
• g