PDPumpGuy
Mechanical
- Oct 3, 2005
- 8
Can anyone help me understand why a Gear Oil with EP additives could potentially cause a a conecting rod journal bearing on a reciprocating pump to fail?
We have had repeated failures of crank pin bearings (the split, insert style, babbit lined journal bearings on the big end of a connecting rod)on a series of reciprocating triplex pumps we have in service, and the manufacturer has blamed our use of a gear lubricant with EP additives as the cause of the problem.
The oil we are using is the same viscosity as the turbine oil they now recommend, however similiar pumps from another manufacturer (National-Oilwell) actually recommend the oil we use, and I can't understand why it would work in one and not the other. Seems to me that, if anything, we would just be wasting money on an oil that we don't really need.
The bearings seem to fail by overheating, then the babbit melts away. It almost looks like they were starved of oil, but we know that was not the case. The only explanation I have heard of why EP oils should not be used with Journal bearings is that journal bearings require a thin film of oil to keep the load bearing surfaces from contacting each other. Apparently, EP oils contain sulfur, and the sulfur migrates to hot surfaces and coats them. Great for gear teeth, but bad for a journal bearing with only .002-.003" of radial clearance for oil to flow.
Seems a bit of a reach, but I would like to see if anyone out their agrees with this theory or has a better understanding of the process.
Thanks
We have had repeated failures of crank pin bearings (the split, insert style, babbit lined journal bearings on the big end of a connecting rod)on a series of reciprocating triplex pumps we have in service, and the manufacturer has blamed our use of a gear lubricant with EP additives as the cause of the problem.
The oil we are using is the same viscosity as the turbine oil they now recommend, however similiar pumps from another manufacturer (National-Oilwell) actually recommend the oil we use, and I can't understand why it would work in one and not the other. Seems to me that, if anything, we would just be wasting money on an oil that we don't really need.
The bearings seem to fail by overheating, then the babbit melts away. It almost looks like they were starved of oil, but we know that was not the case. The only explanation I have heard of why EP oils should not be used with Journal bearings is that journal bearings require a thin film of oil to keep the load bearing surfaces from contacting each other. Apparently, EP oils contain sulfur, and the sulfur migrates to hot surfaces and coats them. Great for gear teeth, but bad for a journal bearing with only .002-.003" of radial clearance for oil to flow.
Seems a bit of a reach, but I would like to see if anyone out their agrees with this theory or has a better understanding of the process.
Thanks