Howden Roots RAS Whispair, Installation, Operation & Maintenance Manual

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ILRB-3000 GEA20261
RAS and RAS-J WHISPAIR Blowers
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arrangement, a variable speed motor or transmission is
required, or air may be vented through a manually
controlled unloading valve and silencer. If discharge air is
returned to the blower inlet, it must go through a cooling by-
pass arrangement.
Before making any change in blower capacity or operating
conditions, contact the nearest Howden Roots office for
specific information applying to your particular blower. In all
cases, operating conditions must be maintained within the
approved range or pressures, temperatures and speeds as
stated under LIMITATIONS. Also, serious damage to the
rotating parts of the blower will result if it is used to handle
air that contains liquids or solids.
Operating Limitations
A Roots blower must be operated within certain approved
limiting conditions to enable continued satisfactory
performance. The Howden Roots warranty is contingent on
such operation.
RAS/RGS and RAS/RGS WHISPAIR blowers are available
with two types of internal blower clearances, normal and
open. Maximum limits for pressure, temperature, vacuum,
and speed are specified in Table 1 for both types of
clearances. Verify with the factory that your blower is
supplied with open clearances before operating it within the
specified conditions. Table 8 lists the values of normal
clearances and Table 9 lists the values of open clearances.
Do not exceed any single limit or combination of limits
listed in Table 1.
Be sure to arrange connections or taps for thermometers
and pressure or vacuum gauges at or near the inlet and
discharge connections of the blower. These, along with a
tachometer, will enable periodic checks of operating
conditions.
Note: Some special purpose blowers may be assembled
with non-standard clearances other than those shown in
Table 8 or 9. These units may be operated at pressure and
or temperature rises higher than those listed in applicable
Table 1. However, you must request specific approval from
the nearest Howden Roots office before doing so,
otherwise the warranty will be voided. Normally, when a
blower is operated at the design conditions stamped on its
nameplate, the specified limits apply.
Pressure - The pressure rise, between blower inlet and
discharge, must not exceed the figure listed for the specific
unit frame size concerned. Also, in any system where the
unit inlet is at a positive pressure above atmosphere, a
discharge pressure of 25 PSI (172 kPa) should not be
exceeded, regardless of blower size.
On vacuum service, with the discharge to atmospheric
pressure, the inlet suction or vacuum must not be greater
than the values listed for the specific frame size.
Temperature - Blower frame sizes are approved only for
installations where the following temperature limitations can
be maintained in service:
• Measured temperature rise must not exceed listed values
when the inlet is at ambient temperatures. Ambient is
considered as the general temperature of the space around
the blower. This is not outdoor temperature, unless the
blower is installed outdoors.
• If inlet temperature is higher than ambient, the listed
allowable temperature rise values must be reduced by two-
thirds of the difference between the actual measured inlet
temperature and the ambient temperature.
Speed - Blowers may be operated at speeds up to the
maximums listed for the various frame sizes. They may be
directly coupled to suitable constant speed drivers if
pressure/temperature conditions are also within limits. At
low speeds, excessive temperature rise may be a limiting
factor.
Special Note: The listed maximum allowable temperature
rise (increase in air temperature between inlet and
discharge) for any particular blower may occur well before
the maximum speed or maximum pressure rating is
reached. This may occur at high altitude, low vacuum or
very low
speed. The unit’s operating limit is always
determined by the maximum rating reached fi
rst −
pressure, temperature, or speed.
ILRB-3000 GEA20261 RAS and RAS-J WHISPAIR Blowers.pdf 4 03/09/2015 13:21:25