Nederman VAC 12/20 Manual De Instrucciones página 22

EN VAC 12/20
that could cause self-oscillating. Rapid movements are hindered by the oil that
must pass by the piston in a small gap between the piston and the cylinder wall.
5.5 VAC 20: Temperature control
High temperatures for long periods may damage the unit. To prevent this,
standard VAC 20 units are fitted with a thermal switch, see Figure 1 Item 8,
linked to a temperature control valve. The thermal switch and temperature
control valve use the same terminals as the start-up valve as power supply. The
temperature control valve opens to permit air cooling if the fan temperature
reaches 79 °C (174 °F). The valve closes when the temperature falls below
60 °C (140 °F). The valve can remain open for long periods at high ambient
temperatures. The valve needs a supply of compressed air.
The fan will run hot and begin 'pumping' if the air flow through the
high pressure fan gets too low. Pumping may not be harmful, but the
jerkiness and irregularity of the pumping sound can be disturbing.
An anti surge control can be used to prevent pumping. See Section
'4.2.1 Optional: Anti surge control' for more information.
5.6 VAC 20: Bearing temperature switches
The circuit trips at temperatures over 110 °C (230 °F) and the unit is stopped.
Thermal tripping results in an error indication in the starting equipment.
Figure 7 shows a circuit diagram for the overheating cut-out for the bearings on
VAC 20. The circuit in the start and control unit must require a manual reset.
The voltage must not exceed 24 V.
5.7 Optional: Compressed air switch
An optional compressed air switch can be mounted in the vacuum unit to
prevent it from starting with no compressed air supply. No air supply must
result in an error indication in the start and control unit.
For electrical connections, see Figure 7 and also the start and control unit
manual. The compressed air switch is wired in series with the thermal fuse.
Use a jumper to connect the terminals if no compressed air switch is used.
5.8 Optional: Anti surge control
Figure 16 shows the main components of the Anti surge control. These are as
follows:
1. Silencer.
2. Valve TVS 76. art no 40144140.
3. Control motor. 24 V AC, art no 40145203.
4. Cable.
5. Current transformer. 100/1 A, art no 40750300.
6. Universal relay. 24 V AC, art no 40721820.
7. Current sensing relay, 2 units MAX and MIN. 24 V AC, art no 40741500.
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