the outside diameter of the impeller wearing ring with an outside micrometer and the inside diameter of the casing-wearing ring with an inside micrometer; the difference between the two diameters is the wearing ring diametrical clearance. By checking the wearing ring clearance with the maximum allowable clearance, you can decide whether to renew the rings before reassembling the pump.
The amount of work in disassembling the pump, the length of time the pump can be out of commission without affecting the command, and whether a repair shop or other repair activity are needed are some factors to consider when determining whether to renew wearing rings.
Wearing rings for most small pumps are carried aboard as part of the command's repair parts allowance. These may need only a slight amount of machining before they can be installed. For some pumps, such as main condensate and main feed booster pumps, spare rotors are carried. The new rotor can be installed and the old rotor sent to a repair activity for overhaul. Overhauling a rotor includes renewing the wearing rings, the bearings, and the shaft sleeve.
OPERATING TROUBLES. - Some of the operating troubles with centrifugal pumps and probable causes are given in table 6-1.
Table 6-1. - Centrifugal Pump Operating Troubles