8
CAUTION: Drive couplings and sheaves (pulleys) should have
an interference fit to the shaft of the blower (set screw types
of attachment generally do not provide reliable service.) It is
recommended that the drive coupling or sheave used have a
taper lock style bushing which is properly sized to provide the
correct interference fit required. Drive couplings, that require
heating to fit on the blower shaft, should be installed per cou-
pling manufacturer recommendations. A drive coupling or
sheave should not be forced on to the shaft of the blower as
this could affect internal clearances resulting in damage to
the blower.
Engine drive applications often require special considera-
tion to drive coupling selection to avoid harmful torsional
vibrations. These vibrations may lead to blower damage if
not dampened adequately. It is often necessary to install a
fly-wheel and/or a torsionally soft elastic element coupling
based on the Engine manufacturer recommendations.
The driver sheave should also be mounted as close to its
bearing as possible, and again should fit the shaft correctly.
Position the driver on its adjustable base so that 2/3 of the
total movement is available in the direction away from the
unit, and mount the assembly so that the face of the sheave
is accurately in line with the unit sheave. This position mini-
mizes belt wear, and allows sufficient adjustment for both
installing and tightening the belts. After belts are installed,
adjust their tension in accordance with the manufacturer’s
instructions. However, only enough tension should be applied
to prevent slippage when the unit is operating under load.
Excessive tightening can lead to early bearing concerns or
shaft breakage.
Before operating the drive under power to check initial belt
tension, first remove covers from the unit connections. Make
sure the interior is still clean, then rotate the shaft by hand.
Place a coarse screen over the inlet connection to prevent
anything being drawn into the unit while it is operating, and
avoid standing in line with the discharge opening. Put oil in
the sumps per instructions under
LUBRICATION
.
Piping
Before connecting piping, remove any remaining anti-rust
compound from Unit connections. Clean pipe should be no
smaller than unit connections. In addition, make sure it is free
of scale, cuttings, weld beads, or foreign material of any
kind. To further guard against damage to the unit, especially
when an inlet filter is not used, install a substantial screen of
16 mesh backed with hardware cloth at or near the inlet con-
nections. Make provisions to clean this screen of collected
debris after a few hours of operation. It should be removed
when its usefulness has ended, as the wire will eventually
deteriorate and small pieces going into the unit may cause
serious damage.
Pipe flanges or male threads must meet the unit connections
accurately and squarely. DO NOT attempt to correct misalign-
ment by springing or cramping the pipe. In most cases this
will distort the unit casing and cause impeller rubbing. In
severe cases it can prevent operation or result in a broken
drive shaft. For similar reasons, piping should be supported
near the unit to eliminate dead weight strains. Also, if pipe
expansion is likely to occur from temperature change, instal-
lation of flexible connectors or expansion joints is advisable.
Figure 3a, page 14, figure 3b, page 16, figure 3c, page 19 and
figures 3d, 3e, 3f and 3g, pages 23 and 24, represents an
installation with all accessory items that might be required
under various operating conditions. Inlet piping should be
completely free of valves or other restrictions. When a shut-
off valve can not be avoided, make sure a full size vacuum
relief is installed nearest the unit inlet. This will protect
against unit overload caused by accidental closing of the
shut-off valve.
Need for an inlet silencer will depend on unit speed and pres-
sure, as well as sound-level requirements in the general sur-
roundings. An inlet filter is recommended, especially in dusty
or sandy locations. A discharge silencer is also normally sug-
gested, even though Whispair units operate at generally lower
noise levels than conventional rotary blowers. Specific rec-
ommendations on silencing can be obtained from your local
Roots distributor.
Discharge piping requires a pressure relief valve, and should
include a manual unloading valve to permit starting the unit
under no-load conditions. Reliable pressure/vacuum gauges
and good thermometers at both inlet and discharge are rec-
ommended to allow making the important checks on unit
operating conditions. The back-pressure regulator shown in
Figure 3a, page 14 in the Gas Section, is useful mainly when
volume demands vary while the unit operates at constant out-
put. If demand is constant, but somewhat lower than the unit
output, excess may be blown off through the manual unload-
ing valve.
In multiple unit installations where two or more units oper-
ate with a common header, use of check valves is mandato-
ry.
These should be of a direct acting or free swinging type,
with one valve located in each line between the unit and head-
er. Properly installed, they will protect against damage from
reverse rotation caused by air and material back-flow through
an idle unit.
After piping is completed, and before applying power, rotate
the drive shaft by hand again. If it does not move with uni-
form freedom, look for uneven mounting, piping strain,
excessive belt tension or coupling misalignment.
DO NOT
operate the unit at this time unless it has been lubri-
cated per instructions.
