Function; Anti Surge Control - Nederman VAC 20 Manual De Instrucciones

EN VAC 20
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.
3.2

Function

VAC 20 is a series of vacuum units that operate for an air flow up to the level specified in
'Table 3-1: Technical data'.
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 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 '4.6 Bearing temperature switches' regarding the bearing overheating cut-out
on VAC 20. See Section '4.7 Optional: Compressed air switch' regarding compressed air
switch.
3.2.1

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.
There are two versions of VAC-20 with the ASC function. One is controlled with the current
transformer and the current sensing relays. The other version is controlled by the PLC in the
HV Control Panel and has the text ASC by PLC on the base label.
18
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 Ø 2 2 - four turns Ø
mm wire 2 mm wire
20-3000 20-4000
3 - six turns Ø -
2,5 mm wire