We have boiler feed water pump driven by HT motor of rating 500 KW, 32 FLA, SKF 6319 at both end with locating bearing at NDE and Non locating at DE. Pump is coupled by gear coupling.
As per previous maintenance history we get high vibration 4.0 mm/s (RMS) at Motor DE axial at 1×BPFI (~14500 CPM) durung motor no load trial just after overhauling (1X is very low, near about 0.7 mm/s). All other points vibration are well bellow 2 mm/s (RMS). we did not get BPFI frequency in radial direction. This problem persist since last long and even after bearing replacement for several times. In coupled condition, we observed same scenario. Sometime BPFI peak goes down upto 2 mm/s (RMS) but it never vanished.
This time after overhauling we get 4.5 mm/s (~14500 CPM - 1X BPFI - SKF 6319) at motor DE axial. No BPFI peak in radial direction. We did some activities and we have two observation as below.
1. When we loose motor drive side mounting bolts axial vibration reduced to 2.3 mm/s (Dominated 1x BPFI). After loosening of all four bolts we get vibration 1.9 mm/s (Dominated 1x BPFI). When we retightened bolts vibration increased to 4.5 mm/s.
2. We carried out bump test on motor DE end bell. We got a frequency at 14466 CPM.
Please explain above behaviour of motor and suggest solution.
Thanks and Regards