1 Description
1.1 Design and Function
The SCREWLINE SP 250 is a dry compressing screw-type vacuum pump
capable of a maximum pumping speed of 270 m
3
· h
-1
at 50 Hz and
330 m
3
· h
-1
at 60Hz.
It has been developed specifically for the special requirements of industrial
applications. Thus the ruggedness of the pump was a main design criterion.
The screw shaped rotors are fitted to two horizontally arranged shafts and
revolve without making contact within the pump chamber. The shafts are
synchronised by a toothed gear. The shafts are driven via a further gear stage
by an electric motor.
In vacuum pumps, the seals and the bearings on the vacuum side are always
a potential source for a breakdown. On the one hand lubricants may enter
from the bearing into the vacuum process and on the other hand aggressive
process media can endanger the bearings.
These disadvantages are avoided by the “cantilevered” arrangement of the
rotors. The SP 250 is equipped with two cantilevered screw type rotors
which are guided by oversized shafts and bearings. The bearings are located
both in the gear chamber of the pump.
A further advantage of the cantilevered arrangement is that the pump cham-
ber is easily accessible without having to disassemble any bearings. Thus any
possibly required cleaning operations necessary due to the influence of the
process can be run easily.
The cantilevered rotors minimise the risk of bearing damage and also reduce
on-site maintenance to a minimum.
Shaft seals are in the case of the SP 250 pump only required on the delivery
side of the rotors. Owing to the small pressure difference between discharge
and gear, simple and reliable seals can be provided. The two shaft seals con-
sist of a combination of a piston ring and a labyrinth seal thus making almost
no contact so that the seals will be almost free of wear.
In standard applications no purge gas will be required at the seals. However,
if demanded by the process conditions, a purge gas may be supplied to the
seals. In the case of ATEX applications operation with purge gas is an abso-
lute requirement.
The SP 250 is air-cooled, a radial fan supports the cooling effect for the hou-
sing which is equipped liberally with cooling fins.
Depending on requirements, the screw pumps may be combined with Roots
pumps so as to attain higher pumping speeds at lower pressures.
Screw rotors
Cantilevered bearing
Shaft seal
Purge gas
Cooling
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