Nederman VAC 12/20 Manual De Instrucciones página 19

VAC
Compressed air quality
Required air pressure
Maximum air consumption intermittent
Material description
Material recycling
FR 160 spring, see Figure 3.
* Motor weight included.
** With optional silencer.
4.2 Function
VAC 12/20 is a series of vacuum units that operate for an air flow up to the
level specified in 'Table 4-1: Technical data'. VAC 12 operates at 12 kPa (48"
W.G.) vacuum and VAC 20 operates at 20 kPa (80" W.G.) vacuum.
Units are delivered with different capacities, voltages, and frequencies. The
motor is a 3-phase asynchronous motor. The motor power matches the unit's
capacity. The vacuum source is a belt-driven high-pressure fan. The power
consumption of the fan increases with increasing air flow. It is necessary
to minimise the power requirement during Y/D - starting. This is done by
restricting the air flow while the motor is operating in Y-mode.
VAC 12/20 units have a start-up valve at the fan inlet. The valve is, apart from
a small leakage flow, closed when the unit is at stand still and during start up
in Y-mode. The valve will open when the motor switches over to full power in
D-mode. The valve is controlled from the unit's start and control unit.
See Section '5.6 VAC 20: Bearing temperature switches' regarding
the bearing overheating cut-out on VAC 20. See
Section '5.7 Optional: Compressed air switch' regarding compressed air switch.
4.2.1 Optional: Anti surge control
A high pressure centrifugal fan operating with too small an air flow, will
run in a surge. This means that the operation is not stable. A characteristic
'pumping' or 'breathing' sound can be heard and the air stream at the fan outlet
will be uneven. The vacuum generation is unstable and this can, under certain
circumstances, cause the ducting to move in rhythm with the pumping.
The motor current is closely related to the air flow through the fan. By
monitoring the current by means of a current transformer in the start and
control unit, it is possible to determine whether the flow is small enough to
cause a surge. If this is the case, a valve inside the vacuum unit will gradually
open to let some more air into the fan.
Figure 8 shows the wiring between the high vacuum start and control unit
and Anti surge contro
transformer monitors the motor current for phase L1. The signal is hard-wired
to the relay box where it passes through two current sensing relays called
MAX and MIN. See the left part of Figure 20.
The MIN relay will be activated if the current is smaller than a set minimum
value (opening the valve).
12-3000 20-1500 20-2500
Clean dry, ISO 8573-1 class 5
6–8 bar (87–116 PSI)
70 N-Litres/min (2.5 cfm)
Powder coated steel, copper, stone wool insulation.
Approximately 95% to 97% of the weight.
- 1 - six turns 2 - four
Ø 2 mm turns Ø 2
wire mm wire
l
. Figure 17 is the electrical circuit diagram. The current
VAC 12/20 EN
20-3000 20-4000
3 - six turns -
Ø 2,5 mm
wire
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