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MD
ND
HD
2
2
3.2.2 By-Pass Valves.
Two spring-loaded by-pass valves are provided between HP-/
MP and MP- /LP stages. These valves have the following
functions: when the pump is started at atmospheric pressure,
the valves open owing to the excess pressure between stages.
This excess pressure is due to the greater suction capacity of
the LP-stage. The gas now flows directly into the exhaust until
the pressure between stages falls below atmospheric pressure
owing to the lower suction.
3.2.3 Cooling
The entire VLV range is air-cooled. A centrifugal fan is mounted
on the pump driving shaft between drive motor and LP-stage. It
draws fresh air between HP-stage and oil reservoir. The air
rises through ducts in the casing of the individual stages and is
expelled by the fan.
3.2.4 Lubrication
An oil lubricating pump, supplying fresh oil to the compression
chambers of the 3 or 2 stages and to the upper rotor bearing, is
mounted on the fresh oil reservoir. The VLV-2 oil lubricating
pump has 4 lubrication points and the VLV-3 has 6.
The lubricating oil flows from the upper rotor bearing, through
orifices in the casing cover and a pipe, to the lower rotor bearing.
It then flows into bearing cover B which lubricates the oil pump
drive. From this container the oil passes through an overflow
orifice, back into the fresh oil reservoir.
3.2.5 Oil separation
The oil-containing exhaust flows from the HP-stage into the
used oil and condensate reservoir. A large proportion of the oil
separates from the air.
The remaining oil is then separated in the oil mist separator in
candle filters which are over 99% effective. Technically pure air
is obtained at the outlet.
3.2.6 Sealing of stages
LP- and HP-stages are sealed from the bearing chamber by two
respective shaft seals.
Shaft seals which come into contact with the suction medium
are made of PTFE, Viton being used elsewhere.
The rotor bearings do not come into contact with the suction
medium.
3.2.7 Drive
The drive is transmitted from the motor to the compressor
stages directly by a flexible coupling.
3.2.8 Standard VLV design
• Flange connections according to DIN 28404
• Stainless steel oil mist separator
• Brass level switch (fresh oil reservoir)
• Stainless steel level switch (condensate and used oil res-
ervoir)
• Grey cast iron condensate and used oil reservoir
• Exhaust connection in 3 different directions is possible (see
D 140 and D 141)
Construction VLV
Drive motor
Cooling air exit
Oil separator
Exhaust air connection
Level control
Waste oil- and
condensate drain
Condensate- und
waste oil tank
Fresh oil tank
Level control
Oil metering pump
Vacuum connection
Manometer for
separator control
(Optional extra)
Cooling air entry
Measuring points
