Function; Main Components - Nederman RBU Serie Bedienungsanleitung

4.2

Function

The RBU (Roots Blower Unit) is a series of vacuum units fitted with a 3-lobe roots pump
vacuum source. See 'Table 4-1: Technical data' regarding airflow information. The motor is
a 3-phase asynchronous motor. See the RBU unit machine tag for details regarding voltage,
current, motor power, and frequency.
The root pump's power consumption increases with increasing vacuum and decreasing air flow
(pump characteristics).
It is necessary to minimise the power requirement during Y/D-starting. This is done by opening
a solenoid valve for free admittance of air to the pump when the motor runs in Y-mode.
All RBU units are fitted with a combined start up and vacuum limiting valve. This valve is
controlled by a low friction compressed air cylinder, a solenoid valve and two regulators. The
valve opens if the vacuum reaches the working vacuum level or the safety vacuum level. When
the valve opens incoming air lowers the vacuum. The opening of the valve will depend on (1) the
vacuum in pump and (2) the force of the low friction compressed air cylinder pulling the valve
in opposite direction. The force in the compressed air cylinder rises when air pressure fed to the
compressed air cylinders raises. In this way, the regulators adjust the vacuum by affecting the
valve disc position which in turn changes the air pressure to the compressed air cylinder.
The working vacuum level is adjusted using the regulator closest to the cylinder, see Figure 1
item 15. The level is set before delivery and no further adjustment is normally required. See
Section '9.11 Vacuum level' regarding regulator adjustment.
CAUTION! Risk of equipment damage.
The safety valve regulator must never be adjusted, Figure 1 item 16. Incorrect setting of the
safety valve regulator damages the pump and the guarantee will be rendered invalid.
At the universal valve entrance is a rubber disc back flush valve. The valve is used when two
or more RBU units are hooked up in parallel and prevents units not yet started from running
backwards.
A rubber disc overpressure valve is placed on the universal valve side, see Figure 1 item 18. The
overpressure valve opens and lets air out if the pump runs in the wrong direction during the
initial start up.
After the universal valve, the air passes through the inlet silencer to the roots pump. Underneath
the pump is a rigid discharge silencer. An additional spiro bend silencer leads the air out from the
unit.
A thermal fuse is placed in the lower flange of the pump, see Figure 1 item 10. This fuse trips at
≈ 140 °C (≈ 284 °F) stopping the unit. The start and control unit will then indicate an error. See
Section '9.7 Thermal fuse' for more information.
An optional compressed air switch can be mounted in the vacuum unit to prevent it from starting
with no compressed air supply.
5

Main components

Figure 1 shows the main components of the RBU unit. These are as follows:
1. Inlet silencer.
2. Outlet spiro silencer.
3. Noise-absorbing enclosure.
4. Spiro silencer with a 90° bend.
RBU EN
13