Wilo VT - Examination of Internal Components

Installation and operating instructions WILO Mather and Platt – VT pumps 38
11.3.3 Disassembling of pumping stages
• Pumping stages assembly consists of strainer, suction bell
mouth, diffuser casing, impeller, pump shaft, rising main
pipe (bottom), etc.
• Remove the fasteners securing to diffuser casing and the
rising main pipe (bottom) and lift the rising main pipe off
the pump shaft.
• Remove rising main pipe (bottom)
• Lift the rotor assembly and put it horizontally on the floor
• Remove the strainer and the suction bell mouth
• Remove diffuser/bowl assembly and the impeller nose
cap/ impeller lock nut.
• Remove the impellers one by one, neck ring and wear ring
(if required and found damaged / not suitable for further
usage) along with grub screw from diffuser casing as per
the drawing. It may be necessary to apply heat to the
impeller for removal. Apply heat uniformly from the
shrouds inwards towards the hub. Before removing the
impeller put a reference mark on the shaft for ease of re-
assembly at correct center position.
• Remove the pump retainer rings, bush from the
diffuser/bowl assembly if required and found damaged /
not suitable for further usage).
11.4 Examination of Internal Components
• With the disassembled rotating element, the internal
components, sleeves and clearances can be checked
(replace if required and found damaged / not suitable for
further usage)
11.4.1 Casing neck ring
Use an internal micrometer to measure the bore of
casing ring, taking measurements at intervals around the
circumference to check for uneven wear. A comparison
between this dimension and that of the impeller neck will
indicate the amount of diametrical clearance between
the casing neck ring and the impeller neck. If this
clearance is 150% or more than the original design
clearance, or if the deterioration in hydraulic
performances has been such that no further
deterioration can be tolerated during the next operation
period, the neck ring should be replaced.
The impeller-wearing ring to casing neck ring clearance
must be restored to the original design value by fitting
small- in-bore neck rings, bored out to suit the diameter
of the impeller.
11.4.2 Shaft Sleeves
The shaft sleeve should be examined to see if it is
grooved or generally worn. The outside diameter of the
sleeve should be measured, and a comparison made with
the bore of the stuffing box bush through which the
sleeve passes. The amount of clearance between the two
can thus be checked to determine whether or not it is
within acceptable limits.
11.4.3 Impeller
Inspect the impeller as follows:
• Examine the impeller for damage.
• For corrosive /erosion pitting.
• Cavitations pitting.
• Bent or cracked vanes, inlet and outlet vane end wear.
If damage is extensive, impeller may need replacement.
Further information should be sought from WILO Mather and
Platt before any decision on repair work is undertaken.
Around the eye, wearing rings protects the impeller. Examine
around the eye at neck portion for grooving in alignment with
spindle axis; slight grooving is acceptable, but deep or
profuse grooving must be remedied by machining the
impeller by taking a polish cut on wearing ring. Spare wear
rings are supplied with excess outside diameter to facilitate
machining after fitting. The wear rings are shrink fitted on
impeller neck and are screwed to check wear around the
impeller neck, use precision instruments such as outside
micrometer to accurately measure the outside diameter.
Measurements should be taken at intervals around the
circumference to check the uneven wear. Differences
between the neck OD and the neck ring ID measured will give
us the clearance between the two. Clearance thus obtained
should not be more than 150% of maximum designed
clearance.
11.4.4 Shaft & keys
Shaft should be checked for the trueness, or any other
mechanical damage and corrosion. If the shaft is not true
within 0.1 mm TIR (Total Indicated Reading), it should be
replaced / repaired. Examine the shaft keys and keyways.
Remove damaged or worn out keys.
11.4.5 Bearings
Check that bearing rotates freely and smoothly, verify that
the outer ring presents no abrasions or discoloration. If there
is any doubt regarding the serviceability of the bearing it
should be replaced.
The re-filling must take place each 1000 hours of operation
and the grease fully replaced every 3000 hours or earlier if the
local prescription requires it.
For oil lubricated bearing oil should be replaced for every
2000 hours of operation.
11.4.6 Mechanical seal
Ensure that the sliding face do not present any scratches or
abnormal wear. Verify that the driving collar is well screwed
on the shaft at the right place. Check that no material blocks
the spring action.