GOK GWD, Assembly And Operating Manual

Page: 17 / 72

Limit indikator GWG type GWD
Part no. 15 382 56 b 5 / 12
LEVELS ACCORDING TO EN 13616
Table 4:
Levels
The limit indicator consists of a height-adjustable probe tube.
The GWG is installed vertically into the tank with an insert.
The connection line of the overfill protection device is
connected to the road tanker using a connector.
Level L
1
At this level, the process of filling is interrupted or reduced
significantly. The level is set in such a way that the level
L
2
is
not exceeded when draining the road tanker and the filler line.
Level
L
1
is the reference dimension for the
adjusting
dimension X .
Level L
2
Regarding this level, any further addition of operating medium
is prevented when filling the tank prior to or when reaching the
maximum level L
max
of the limit indicator.
Admissible level L
max
Level at admissible level according to table 5 .
Marks on the limit indicator
The limit indicator has two marks:
• Probe length
Z
in mm, impressed permanently, with notch,
must be visible upon installation
•
Switching point of the sensor for L
1
.
If required, the probe tube protruding from the
tank must be protected against mechanical loads, e.g.
pressure, impact, or vibrations.
CONTROL DIMENSION Y = Z - X
Clearance between upper mark for Z and upper reference edge tank.
Mode of operation of a limit indicator
Regarding the function of the limit indicator, the principle of a temperature-
dependent electrical PTC resistor is used - also referred to as PTC thermistor or
sensor. The resistance of the PTC thermistor creates a current.
If, during filling, the GWG is connected to the controller of the overfill prevention
mechanism on the road tanker with the help of a line, the GWG is supplied with
voltage. The PTC thermistor heats. The change in temperature causes the
approval signal and the controller opens the cut-off valve on the road tanker.
Once the escaping liquid makes contact with the PTC thermistor at level L
1
in the
tank, the PTC thermistor cools down and the electrical resistance changes. This
change in resistance causes a change in current in the GWG circuit. As a
consequence, the controller immediately stops filling by closing the cut-off valve
on the road tanker.
The process of filling shall be terminated at the latest when reaching the
maximum admissible discharge volume previously determined by the road tanker
driver.
It shall be inadmissible to deliberately fill until shutdown by the limit indicator when the
admissible level is reached.