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Ball Mills Losing High & Low Lube pressure (6 replies and 1 comment)

5 months ago
JB 5 months ago

One of our Ball Mills keeps losing pressure on the high pressure pump. It will run fine when starting the Mill and suddenly after a while sometimes 1hrs the pumps will loose pressure. We have just grinded the journal and installed new white metal bearings. After startup this afternoon after about 1hrs the pumps low and high just lost pressure. We have cleaned the whole lube system and filled with new Carter XEP 460 oil. We had in Carter 320 before and had no problem, problems started right after the oil change. We did put in new HP pumps and it lasted 1 day. Please help!

5 months ago
David 5 months ago
1 like by Wayne

Hi and welcome to 911Met,

It "sounds" like you have a problem with the oil filter - either by-passing or not meeting the necessary micron spec. I changed to a cheaper filter (Pall) once with the same micron spec as the original, but it wasn't doing the job and I burned out all of the Bosch HP pumps of their kind in North America before the problem was corrected (WIX).

It also could be your low PSI pump is cavitating and can't get the oil out fast enough as it it too weak for the new thicker oil you got... check that and maybe also increase the diameter of the pump suction piping to ease the inlet delivery.

That said, the oil change should have prolonged the life of the HP pump, but the viscosity change now points to a more likely suspect - the HP pump is starving and cavitation is destroying the tolerances in the pump internals. If the HP pump is gravity fed (from a separate "clean oil" sump) then it may be necessary to increase the diameter of the pump suction piping to ease the inlet delivery. If the HP pump is fed directly from the LP pumps (via filters), then check the pressure drop across the filter, the setting on the pressure relief valve (may be by-passing), and the suction piping diameter on the LP pumps (they may be cavitating also, or simply not delivering enough volume).

If the bearings have a built-in dynamic wedge, it my not be necessary to keep the lift pumps on when the mill is running (short-term fix perhaps). This dynamic lift could also be relieving the HP pump discharge pressure and exacerbating the cavitation.

Another short or long-term fix may be to revert back to the lower (or an intermediate) viscosity lubricant until the system can be modified to handle the thicker stuff - larger pipes, more suction head (raise sump or lower pump to increase suction head), and perhaps a different HP pump altogether.

And last suggestion, though obvious and likely already considered, the oil level in the reservoir...the marks on the sight glass should indicate "running" and "idle" conditions to account for oil line filling and drain-back. If there is room to bump the level up a bit, this could help with the cavitation.

Check viscosity of oil and suction restrictions.

Thanks to Craig Lockhart for his input on this.

Paul Morrow
5 months ago
Paul Morrow 5 months ago
2 likes by David and Wayne


our friend https://www.911metallurgist.com/profile/cjlockhart/ provides this:

A single 1" manifold was supplying a 1" suction hose to the LP pump and two 3/4" suction hoses to the HP pumps, starving all 3...  I replaced with a 2" manifold and 1 X 1.5" LP and 2 X 1" HP suction hoses - problem solved.

Ball Mill Lube Pump manifold t hold pressure modification

Ball Mill Lube Pump manifold t hold pressure

Craig Lockhart
5 months ago

Another indication that your pumps are cavitating is noise - if your pumps are howling, growling, whining or are otherwise abnormally loud, they are probably starving. If you make a change and the pumps get quieter, you are probably onto the solution...

5 months ago
Hauptsturm 5 months ago

First question is why the oil type change, is it bypassing into tank, what do the filters look like, is there excess oil leaking from the trunnion area and simplest is the rotation correct on the new pump, if grinding took place did the mill trunnion sump get cleaned, not knowing the type of mill this is where we start.

Sugar Watkins
5 months ago
Sugar Watkins 5 months ago
  • What kind of pumps are they using?
  • Are they Vane or gear pumps?
  • Are there any Pressure relief valves or check valves in the system?
  • What weight of oil is the Mill Manufacture recommending?( this 460 oil seems very heavy to me.)

I know Gibraltar had lube pumps and (I call them) dip cups, which were cups attached to the trunnion that would turn with the mill filling with oil pouring over the trunnion as the mill was turning. this is old school.

How old are these mills?

One final note: Pressure is resistance to flow, so you are saying there is no pressure, that would mean there is no flow which would mean your pump is not pumping. some pump design are made to by pass internally. thats why I ask what type of pump.

5 months ago
David 5 months ago

Better lube package designs nowadays have vertical pumps mounted in the top of the sump.Better lube package designs nowadays have vewrical pumps mounted in the top of the sump

Thanks to Craig Lockhart for his input on this.

Ball Mill Trunnion Bearing Lube System

5 months ago
JB 5 months ago
2 likes by Craig Lockhart and David

Thanks guys, to answer a few of the questions:

The HP pump we are using is a gear pump and the reason for the oil change on the lube from 460 to 320 was that for around 6 years we have used Carter XEP 460 on the fix side and Carter EP 320 on the float side. As we wanted to go to a common oil and  recommended by supplier we opted for 460 on both sides. The problem with the HP started straight after we changed to that. As if the pump could not get suction.As we  were loosing to much run time trying to sort the problem and obviously running out of pumps I instructed to go for the thinner oil and we had no problem since. Very strange as I do not feel comfortable with this as it does not make sense because the HP runs 100% on the fix side with 460 oil. I definitely like the flooded suction idea as our pump are positioned on top of the tank with a suction pipe leading into the pump from the bottom.

Must add that the instruction was given to keep the tank level full at all times even when running, that could have been one of our problem that the oil level in the tank was low and the pump was making a vortex at the suction but we are still going through all and the help from all are definitely implemented as well.

Thanks and much appreciated   

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