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3. General Construction
3.1 General
The Rietschle TWISTER pumps gases and vapours by use of two screw rotors, hav-
ing a profile comprising a plurality of curves, i.e. Archimedean curve, Quimby curve
and arc, which rotate smoothly with a certain clearance maintained between each
other and inside wall of the casing.
The gases and vapours being pumped are smoothly pressurised up to the pressure
on the discharge side. The pump is so constructed as to prevent oil from entering the
pumping chamber. The power of motor is transmitted to the main rotor shaft through
V-Pulley or a coupling device, and then to the driven rotor shaft through a timing
gear.
3.2 Construction
• Rotor shaft: The rotor shaft is
made of high grade spheroidal
graphite cast steel, and preci-
sion machined through numeri-
cal control by a special ma-
chine. It is perfectly dynamically
balanced after the rotor is ma-
chined.
• Timing Gear: The timing
gears are the most important
part of the screw vacuum pump, and
they are required to maintain the precision clear-
ance between the rotors. The tooth surface is heat cured,
and then polished with a special high precision tooth polishing ma-
chine for noise reduction.
• Bearing: The bearings on the fixed end are angular contact ball bearings and on the float-
ing end are roller bearings of heavy load capacity. These bearings have been selected for high speed and heavy load service
and to assure the accurate maintenance of clearances between gears and between rotors.
• Shaft Seal: The shaft seals consist of twin lip seals on suction side and bellow type mech. seal on discharge side. These
seals prevent oil passage from front end plate to the inside of the pumping chamber. Front end cover side of drive shaft is
sealed by an oil seal.
• Oil Level Gauge: The Oil Level Gauge is located in the Front End Cover. Oil should be supplied to the top level of Red mark.
If the oil level is too low, Gear, Bearing and Mechanical Seal will be damaged as a result of improper lubrication. The timing
gears, bearings and mechanical seals are splash lubricated. Check oil level and look for contamination when the pump is
stopped.
3.3 Specifications
VSA
Nominal (theoretical) Displacement
Ultimate vacuum
Discharge pressure
Motor rating
Speed
Port size (Suction / Discharge)
Gear oil
Max. internal pressure
Cooling water
Cooling water pressure
Cooling gas
Sealing gas
Seal type
Weight
Note:
(1) The quantity of oil listed is only for reference, and surplus should be available. It should be noted that fluorine and mineral
based oils can be used. For shipping, we supply pure gear oil.
(2) The Cooling Water flow quoted is based on water temperature of 20° C. The amount of water will vary when using an After
Cooler. Please check with Vendor's approved drawing.
50 Hz
m³/h
60 Hz
mbar (abs.)
bar (abs.)
50 Hz
kW
60 Hz
50 Hz
-1
min
60 Hz
DN
bar (abs.)
l/h
bar (abs.)
3
m
/h
cm³/min
Front end plate
Rear end plate
Front end cover (drive shaft
kg
150 (30)
330 (30)
120
270
150
330
0,3
0,3
4,0
7,5
4,8
9,0
40
50 / 40
l
1,3
1,6
240
480
18
Bellows type mechanical seal
330
520
- 4 -
400 (20)
360
400
0,05
max. 1,3
15
18
2850
3450
65 / 50
2,0
10
660
max. 6
18
25
max. 3
Lip seals
Oil seal
610
800 (20)
720
800
0,05
18,5
22,0
100 / 65
4,0
1200
> 30
810
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