I am working in thermal power plant and look after the Maintenance of Boiler and it's auxiliaries.
PROBLEM: for lubrication of fan bearing separate lube oil system is used, which has 2 pump, one as working and other standby.. During pump changeover, standby pump often do not develop pressure due to air ingress. So whenever this problem occur, we loose pump discharge NRV bolts and remove air locks from their, and after removing air locks pump starts to develop pressure.
Every possible measure was done to arrest air locking but still right solution is far from reach.
Pump specs : SCREW PUMP
Flow: 40 LPM
Please put some relevant light on this subject.