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Remove the front-end cover securing screws, front cover, wear plate and paper joints. If the vane is worn, the contact radii will appear flattened at the ends. Revolve the pump internals through 360 degrees, inserting a feeler gauge between the vane and the casing sleeve. The design clearance is 0.008" or 0.2032mm, whilst the maximum operational clearance is 0.012" or 0.3048mm.
Removal of rotor/shaft assembly
Remove the drive coupling half from the shaft and remove any burrs from the pump shaft extension. Remove the two adjusting nuts from the gland assembly and then the gland pressure pad. Remove the rotor and shaft as one unit. Check the shaft diameter where it revolves in the main bearing - the design diameter is 1.498" or 38.04mm, with a maximum reduction of 0.003" or 0.076mm.
Examine this for wear. The internal shape of the sleeve is not a perfect circle and must not be re-machined. To remove the sleeve, remove the back-end cover securing screws and the cover itself. When fitting a new sleeve, ensure that the anti-rotation pin is replaced.
THE INTERNAL BORE OF THE PUMP IS NOT CIRCULAR, AND SHOULD NOT BE RE-MACHINED.
Examination of the bearing bush and ballrace
To check the main bearing bush, separate the bearing-housing casting from the back-end cover by extracting the securing screws. Place the rotor/shaft assembly on a bench and slide the bearing-housing casting along the shaft to approximately its normal operating point. Rock it on the shaft to establish wear. If a new bearing bush is necessary, press out the original and fit a new bush, ensuring that the grease hole in the bush corresponds with the grease nipple in the bearing-housing casting.
To replace the front-end ballrace, remove the thrust plate and oilseal, and then push the ballrace out from the oilseal side of the front cover.
Examining the rotor for wear
First establish the degree of clearance between the outside diameter of the rotor and its contact point with the bore of the casing sleeve. Assemble the back-end cover and back bearing housing assembly using two screws. Bolt this to the casing using sufficient for rigidity (some clearance is provided on the back-end cover spigot). Replace the rotor/shaft assembly into position in the pump casing and check the clearance using a feeler gauge. Apply light upwards pressure onto the rotor to ensure the assembly has not dropped. The maximum clearance between the rotor and the casing should be 0.004" or 0.1016mm. If the clearance exceeds this, check that the back-end cover is raised to the highest point.
It is recommended that vanes are replaced with spares from the manufacturer, particularly in corrosive and/or abrasive duties. In urgent non-corrosive and non-abrasive applications, vanes can be built up by arc-welding, re-hardened and re-machined.
Assemble the back-end cover and back bearing-housing using a light application of liquid jointing compound between mating surfaces. Secure the back-end cover, ensuring that the anti-rotation pin is in position in the casing sleeve. Fit the vane into the rotor slot and replace and revolve the internal assembly. Remove any tight spots by scraping or grinding. However, on no account must scraping or grinding be carried out on the casing sleeve.
Once the pump internals revolve freely, check the rotor to casing sleeve clearance as before. Lightly striking the outer edge of the back-end cover with a soft-faced hammer will position the back-cover correctly. The front-end cover is sealed by two paper joints either side of the wear plate. These components should be secured to the casing as one unit. Ensure that the oilseal is not damaged. Replace the front-end cover securing screws and part-tighten, whilst slowly rotating the pump internals with a lathe driver or a coupling half secured to the shaft extension. Once the pump revolves freely, tighten the securing screws.
Pack the ballrace housing with suitable grease. Replace the thrust plate, ensuring that the screws are slackened off. Once secured, screw in the thrust screws until the pump internals cannot revolve. Release the screws evenly at ¼ turn intervals, lightly striking the end of the shaft extension between each turn until the pump internals revolve freely. Tighten the thrust screws.
Except for pumps with mechanical seals, fit new gland packing. Replace the gland pressure pad, bur do not over-tighten as serious shaft wear can occur. Leave the final gland adjustment until the pump is returned to service.
A weekly application of Shell Alvania 2 grease, or equivalent, to the main bearing lubrication point and inspection of the gland is the normal extent of routine maintenance.
Gearboxes of various makes are fitted to comet marine pumps. Grease lubricated gearboxes are normally supplied filled and sealed for approximately 10,000 hours operation, after which grease should be removed and the gearcase flushed out before refilling with the appropriate grease. The gearbox nameplate should be referred to for the gearbox manufacture's recommendation as to the grade of grease.