A purge supply of 2 USgpm minimum should be maintained throughout the entire chemical cleaning operation on ALL pumps in situ, regardless of whether the motors are energized or not, unless the pumps can be isolated from the system, and this isolation ASSURED.
The purge pressure should be no less than 25 psig above the system pressure at the discharge of the pump. The purge pressure will be greatest for the pump/motors that are energized. Cooling water should be maintained to all energized motors and to all motors which are exposed to elevated temperature.
Generally, the operation of a single pump is not recommended as this can result in abnormal wear on the thrust bearing as the pump seeks to intersect the system head curve at lower friction losses. However, the wear sustained during limited operating times for acid cleaning should be within acceptable limits. Pumps that have been in service for extended periods without inspections to end float may have limits exceeded after completion of the acid clean operation.
UNDER NO CIRCUMSTANCES SHALL THE DRUM AND DOWN-COMER SYSTEM BE DRAINED THROUGH THE FILL AND DRAIN CONNECTION OF THE MOTOR.