4 replies to this topic

[ASH25320]

We have a Six stage centrifugal pump running at 6500 RPM @ 60 m3/Hr capacity delivering pressure of 165 kg/cm2. This pump has a shaft mounted lube oil pump for bearing lubrication which takes over after main pump is started, then the auxiliary L.O. pump is stopped. The practice till now was to keep aux. L.O. pump running if main pump is stopped & hence oil circulation is kept continuously. Now from power saving point of view we have kept this Aux L.O. pump in stopped condition. is it a good engineering practice? Does it harm the main pump in any way?....

[benabed]

We have a Six stage centrifugal pump running at 6500 RPM @ 60 m3/Hr capacity delivering pressure of 165 kg/cm2. This pump has a shaft mounted lube oil pump for bearing lubrication which takes over after main pump is started, then the auxiliary L.O. pump is stopped. The practice till now was to keep aux. L.O. pump running if main pump is stopped & hence oil circulation is kept continuously. Now from power saving point of view we have kept this Aux L.O. pump in stopped condition. is it a good engineering practice? Does it harm the main pump in any way?....

Good day;
I think it is not a good practice at all. You should keep the auxilliary pompe in automatic mode ready to start in the event of the main lub oil pompe failure.
ragaards;
Benabed

[Padmakar Katre]

Dear,
This is my first time I read that the pumps have lubrictaion pumps anyways if so my suggestion to you to keep the aux lube oil pump running.Now I will justify my reply see normally I found this lubrication pumps in reciprocating compressors which are started for minimum 30 min or 1hr (it's not standard only you have to ensure the proper circulation of lube oil prior to start your comressor) and as soon as the compressor is started its inbuilt lube oil pump will be started and you will stop the aux lube pump and keep it in AUTO mode as soon as your comressor has shut-down this aux pump will start and ensure the cooling of the bearings.
Now the same thing will happen with your pump as soon as it will have shutdown your aux pump (in AUTO mode) will take over and provide cooling but my concern is with the standby pump which you need to start immediately (within no time to avoid interruption in your contineous opertaion) as soon your running pump finds problem.So for this reason you have to keep the aux pump running contineously as you don't know anything about the lube oil pump mounted on your main pump.If it doesn't start or faces any problem then it will upset your process.
My above reply is subjected to that everyone have the same SPARING philosophy i.e. every running pump will have a standby and not for comressors which will be be one and unique.So prior the compressor start-up you will achieve/establish the proper lube-oil circulation and then you will start it but essentially not the case with pumps everytime.
If you find it is nor logical or usefull please ignore.

[Technocrat]

I suggest that you provide gravity oil feeding mechanism in which an overhead lube oil tank will supply oil to the bearing. The oil shall be collected in tank located at grade and recycled back to elevated tank by a separate oil pump (SOP). This circulation will be continuously on irrespective of the running inbuilt pump. In case of failure of the inbuilt pump and the spare pump do not come in line automatically this gravity flow will take care of the lube oil pressure. Meanwhile one can start the spare pump manually and save the compressor or pump from tripping.

In the worst case when the SOP also do not start there will be gravity circulation of oil through bearing for maintaining lube oil pressure for some time. There shall be sufficient oil stock in overhead tank so that the spare pump can be started before the oil pressure fall below the compresor lube oil pressure trip setting.

[Dharmesh]

We have a Six stage centrifugal pump running at 6500 RPM @ 60 m3/Hr capacity delivering pressure of 165 kg/cm2. This pump has a shaft mounted lube oil pump for bearing lubrication which takes over after main pump is started, then the auxiliary L.O. pump is stopped. The practice till now was to keep aux. L.O. pump running if main pump is stopped & hence oil circulation is kept continuously. Now from power saving point of view we have kept this Aux L.O. pump in stopped condition. is it a good engineering practice? Does it harm the main pump in any way?....

Auxiliary pump should be in running condition if the same is mentioned in the vendor's manual. I think this the general procedure in most of the cases that auxiliary LO pump will start automatically before startup of main equipment and after tripping/stop of equipment to keep bearing in cool condition. As this is a case for HP pump it should be in running condition for specified time to allow proper cool down of bearing. In case of some compressor where Inert/recycle gas provided as barrier to LO and inert gas having low temp. LO pump starts not required.