Manual 2003 Rev D p/n 2003
6
Refer to specific data sheets for flow capacities
and vacuum capacities.
OTE:
N
Refer to diagrams in this manual for
proper rotation and orientation in inlet
and discharge.
Tuthill Vacuum & Blower Systems models 150
to 400, 540 to 720, and 850 to 2700 mechanical
vacuum boosters are positive displacement type
boosters, whose pumping capacity is determined
by size, operating speed, and differential pressure
conditions. Vacuum boosters employ rotors rotating
in opposite directions within a housing closed at the
ends by end plates.
The inlet to the discharge is sealed with operating
clearances that are very small. Internal lubrication is
not needed, as there is no moving contact.
Clearances between the rotors during rotation are
maintained by a pair of accurately machined helical
timing gears, mounted on the two shafts extended
outside the air chamber. The intermeshing rotary
lobes are designed to rotate and trap air or gas
between each rotor and the housing. As the rotor
lobes rotate past the edge of the suction port, the
trapped air or gas is essentially at suction pressure
and temperature. Since the booster is a constant
volume device, the trapped air remains at suction
pressure until the leading rotor lobe opens into the
discharge port. The close clearances between the
rotors inhibit back slippage of the trapped volume
from between the rotors and the trapped volume
is forced into the discharge piping. Compression
occurs not internal to the booster, but by the amount
of restriction, either downstream of the booster
discharge port, or upstream of the booster inlet port.
Figure 4-1
illustrates the air movement within the
machine. In addition, the machine can operate in
either direction.
Never attempt to control capacity by means of a
throttle valve in the intake or discharge piping. This
will increase the power load on the drive system,
which will increase operating temperatures, and
can overload and/or seriously damage the booster.
Likewise, if the possibility exists that flow to the
booster inlet may be cut off during normal operation
of a process, install an adequate vacuum relief
valve. A pressure-type relief valve in the discharge
line near the booster is also strongly recommended
for protection against cutoff or blocking in this line.
Use check valves on each booster when more than
one booster is connected to a discharge line.
Vacuum boosters must be protected by cut-in
switches or with bypass valving to limit differential
pressure across the booster.
When a belt drive is used, it is possible to adjust
booster speed to obtain desired capacity by
changing the diameter of one or both sheaves,
or by using a vari-speed motor pulley. In a direct
coupled arrangement, a variable-speed motor or
transmission is required. Gas boosters can use
bypasses, but some applications may require
additional cooling. If there is a large volume of
high-pressure air or gas downstream of the booster,
a check valve in the piping downstream of the
booster will protect the booster from overspeeding
in a backward direction upon shutdown.
DESCRIPTION
04
