Root type Blower - Lube oil issue

[planck121]

We are having issues with pressure/flow of the lube oil system on a roots type (screw)blower. The lube oil is being pumped by an IMO (connected to the shaft) with in the blower housing. The oil is also sitting with in the blower casing and the pump basically pumps the oil to the bearings and then filters it through and cools it down through and exchanger (typical of a lube skid). However, operations has been saying they have observed occasional loss of pressure/flow through the lube oil skid system.

I have only recently taken this problem on hand trying to possibly move into a root cause study. But nothing is popping out of the ordinary at the initial investigation. The only thing I am thinking about is the fact that there is a little screw on the IMO pump itself which is adjusted to control the pressure/flow through the pump and this might be loose or something. But again operation says this happens occassionaly and I'd assume if it is a screw issue on the pump then it should not happen intermittently but should rather continious.

I would like to hear your thoughts, if anyone has had much experience with such lube oil skids on these blowers and potential points of issue.

Thanks and much appreciated.

 

[JJPellin]

Is this system in continuous operation or is it intermittent? The shaft driven oil pump could be loosing prime when the machine is down. Normally, there would be a foot valve to keep the oil from draining out of the main oil pump. Or, there could be an auxiliary pre-lube pump with a prime line to keep the main pump primed. The IMO pump probably has a built in relief valve to prevent over-pressure. But, this is unlikely to result in intermittent problems. If it failed, then the system would stop working. I would check for a suction strainer in the line to the oil pump. It could be plugged up. I would check for a suction check valve or foot valve. It could be sticking open intermittently. I would determine if the oil pump uses a mechanical seal or just a break-down bushing. If it is sealed, the seal may have failed. Often these are set up so that the seal leakage will run right back into the housing and would go unnoticed. If it is a break-down bushing, this could be allowing air to get into the system when it is not running.

Additional details and a diagram of the oil system would help us provide better suggestions.


Johnny Pellin

 

[planck121]

Johnny,
I am attaching the drawings from the operating manuals. The ones I could find on the system. They do not seem to have details drawings on the pump itself. I am assuming it would be a gear pump (not a certifugal) based on what I see on the drawing.

Hope these help in understanding what is going on.

Thanks

 

[planck121]

Looks like it didnt come through in the past post. Reattaching.

 

[planck121]

Johnny,
Just to add to that further details. We have four of these and this lube oil issue seems to happen on all 4 at some point in time or another. The are in continious service. Sometimes they start good and keep running for months and at other times, it seems there are flow issues with the lube oil.

 

[JJPellin]

If you have four of these systems and all of them have occasional problems, they you should concentrate on potential common causes. The first one that comes to mind for me is the lube oil you are using. If the oil is prone to foaming, it could be foaming up which confuses the operators when they are attempting to verify oil level. If foam is introduced into the running pump, it could loose prime and stop pumping. Verify that you are using a high quality oil of the proper ISO grade as recommended by the equipment manufacturer. Consider changing over to a synthetic oil which may have less tendency to foam. Foaming is a common problem in Sundyne gearboxes. We converted to a high quality synthetic made specifically for gas turbine applications. It is rated very good for resistance to foaming and for air release.

The oil pump is probably a screw or gear pump. It would not be centrifugal for this application.


Johnny Pellin

 

[planck121]

Johnny
I concur with you based on some of my observation I am led to believe that the might be loosing prime somehow. Cannot seem to figure out a logical reason yet. Though I had trended on our online system and seems like the lube oil pressure fluctuates with compressor discharge so when the comp discharge spikes up so does the lube oil. However I'm not sure how this can cause a loss of prime it happens on all four of them so bushings clearances seems a bit unlikey and as far as the lube oil goes no frothing was observed .

 

[Tuckabag]

Couldn't open the attached file for some reason......
I would expect that the oil pump would be a small gear pump, they generally have an inbuilt bypass relief to prevent them overpressurizing oil galleries, etc. If this relief is set incorrectly or there are blockages causing the pump back pressure to increase then the relief will contiually pass.
Check the ISO rating as mentioned before, too thick and you may have trouble pumping it as well. Highly recommend synthetic oil, it's all we ever used on our roots blowers, generally ISO100 but this will be manufacturer specific.

 

[planck121]

@Tuckabag
We have had issues in the past with the relief valve setting on these lube oil pumps and yes they are gear type pumps. My understanding is the relief valve adjustment simply controls and directs the flow between and the suction and discharge of the pump (reciculation) to prevent the issue of overpressuration. I believe there could be a problem associated with this since the operators in the field have been playing around with this (in the hope of pressurizing/maintaning lube pressure)...

How do these pump tyically prime themselves? Since they are attached to the shaft and we are running these blowers of VFD I believe it will take a while for the pump to build pressure (as the shaft speeds up) but what about the initial priming how is that achieve (we do not have a footvalve in the system) so does the pump intially run dry and then when it builds up vaccume it starts to suck the oil ....

 

[planck121]

After much head butting with RCA on the root cause blower at our site. It was noticed that the issue lied in the fact that the original lube oil piping on the blower was changed by a third party contractor to comply with company specifications. As a result of the change in the piping from the original vendor supplid piping layout. It seem the pump was not being able to build the required head due to the flow through a longer pipe length as compared to the vendor recommended design. It was informed to us (reliability)that the blower expericined issues only during start-up and not like I mentioned in my initial thread (during running)....anyhow to keep a long story short. The issue was piping layout causing loss of pressure build-up....Once the piping was changed the pump was able to build enough head in the lube oil system.

Thanks for all the good input ...

 

[Tuckabag]

Glad you got it sorted Planck!! Always good to get to the bottom of things like this.

Going back to your 2nd last post, all the units I have worked on have self primed. They generally only needed to lift around 2~4" anyway as the pump was mounted just above the oil level.

Cheers.