Page 4
3
4
VWP 160-3 / 250-3
VWP 400-3
5
3.3 Principle of operation
The INOVAC multi-stage vacuum pump utilises the Roots principle which has been used in
vacuum engineering for over 100 years. The mode of operation is illustrated in pict. 5.
Compression is achieved by two figure of eight rotors, rotating in opposite directions. The
rotor contours are such as to keep the same clearance between rotors or between the rotor
and casing. A Roots blower operates without internal compression of the transported gas.
Compression to a higher pressure is achieved at the exhaust side of the blower, when the air
is exhausted against the existing pressure in the exhaust port. This back pressure causes a
back flow of gases through the rotor gap towards the vacuum side. The higher this back
pressure and the higher the pressure difference between the vacuum and pressure side, the
greater the reduction in suction capacity and greater heat generation of the pumping unit.
This generated heat can only partially be removed via the cooling of the housing and therefore
a danger of over heating and seizure could be possible. This is the reason why a basic Roots
pump can never compress against atmospheric pressure. All Roots vacuum pumps that are
currently available on the market require some degree of intermediate cooling when they are
operating against atmosphere without a backing pump.
INOVAC is the only known Roots vacuum pump that has been especially designed to provide a solution to this problem.
The back flow which causes the excess heat generation of the pump has been eliminated utilising valves on the exhaust side of
the medium and high pressure stages (see pict. 3 and 5).
The vertical arrangement of the three pumping stages prevents condensates accumulating during compression, with natural
drainage making sure that any condensate is exhausted.
A by-pass system fitted between the LP/MP stage and MP/HP stage allows start up and operation of the INOVAC at any level
of suction pressure. Due to the contact free compression, lubrication within the pumping chamber is not necessary. Consequently
lubrication is limited to the drive and bearing areas which are separated from the pumping chamber by rotary seals.
As there are no frictional forces within the chamber, the stages operate at high speeds, approximately 4000 rpm.
Due to the Roots principle operation and the precision dynamic balancing of the rotors INOVAC operates extremely quietly at
these speeds.
3.2 INOVAC sectional drawings
3.2.1 Cross section through compressor stages
1
Bearing lubrication LP
2
Bearing lubrication MP
3
Bypass system
4
Bearing lubrication HP
5
Vacuum connection
6
Outlet valves
7
Exhaust air connection
3.2.2 Longitudinal section INOVAC
8
Sealing
9
Service temperature sensor (VWP 400-3)
10
LP stage
11
Sealing gas
12
MP stage
13
HP stage
14
Cooling pump
15
Main drive
16
Cooling fan
17
Cooling fan motor (VWP 400-3)
