The drain pumps of low-pressure heaters for supercritical units no.1 and no.2 in Huaneng Caohu Power Generation Co Ltd

through tests of many times during initial period of putting them into operation

still can't normally put into service from begining to end.It is believed from analysis that the resistance in drain pump system of low-pressure heater for said units is larger

and the necessary cavitation margin of said pumps can't be reached

thereby

making the exit of drain pumps to produce cavitation

can't satisfy the requirements in continuous operation under heavy load.For this

the first-stage impeller of said drain pumps has been retrofitted into one double-suction impeller.After retrofitting

the cavitation margin of said drain pumps under rated load of 600 MW is larger than the necessary cavitation margin

can keep continuous operation

satisfying the requirements in operation of units.