Page 137 - Introduction to Marine Engineering

Pumps and pumping systems 123

Water
movement

Air
discharge Air
port inlet
ports

discharge
port

Fixed
hub

Figure 6.10 Water-ring primer

can be slowly opened and the quantity of liquid can be regulated by
opening or closing the delivery valve. When stopping the pump the
delivery valve is closed and the motor stopped.
Regular maintenance on the machine will involve attention to
lubrication of the shaft bearing and ensuring that the shaft seal or gland
is not leaking liquid. Unsatisfactory operation or loss of performance
may require minor or major overhauls. Common faults, such as no
discharge, may be a result of valves in the system being shut, suction
strainers blocked or other faults occurring in the priming system. Air
leaks in the suction piping, a choked impeller or too tight a shaft gland
can all lead to poor performance.
When dismantling the pump to remove the pumping element any
priming pipes or cooling water supply pipes must be disconnected.
Modern pumps have a coupling spacer which can be removed to enable
the pumping element to be withdrawn without disturbing the motor: the
impeller and shaft can then be readily separated for examination. The