Howden 24-07.030r04 15/25
E-series Axial Flow Cooling Fans
To make sure that the tip clearance is not less
than 0.25% in any location we recommend the
following steps:
a. Determine the longest blade by measuring
the tip-clearance of all blades at a fixed
point in the fan casing.
b. Now measure the tip clearance of the long-
est blade at a number of measuring points
(see table 4 for the number of recom-
mended measuring points). Slowly rotate
the impeller by hand to the different meas-
uring points.
c. Centre the impeller in the casing, or the
casing around the impeller, in case the tip
clearance is too small and repeat the previ-
ous steps.
Number of meas-
uring points
Table 4
Impeller diameter reduction
In case the tip clearance is smaller than the
above described minimum tip clearance, and
centring the impeller does not help, one has the
possibility to reduce the impeller diameter by
placing one or more 5 mm thick nylon spacer
rings between the blade stem collars and the
lower clamping pieces. The same number of
spacer rings shall be installed on all blades of
an assembly. This method allows the impeller
diameter to be reduced by 40-50 mm.
After installing the nylon rings, torque the nuts
again according to the blade installation proce-
dure as described previously.
Retaining plate
(Supply of retaining plate is optional).
Install retaining plate with gasket, washers and
bolts after the coupling flange or after the im-
peller has been installed. For torque values of
electro-galvanised retaining plate bolts see
table 7 on page 22 of this manual.
Important
Howden strongly recommends the
installation of a retaining plate for all
vertical shaft applications with impeller
hanging below the driver or whenever
the airflow is directed towards the
driver.
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