BEARING HOUSING SEALS FOR FORCED FEED LUBRICATION SYSTEMS

Rotating machines with oil-fed bearings are susceptible to oil leaks from the bearing case seals. Compressors, turbines, motors, gearboxes, and pumps that use forced feed lubrication systems can all suffer from oil leaks. These leaks can represent anything from a housekeeping nuisance to a risky fire hazard. Our team at GCBS (Gulf Coast Bearing and Seal) can help you eliminate these headaches with custom-fit oil seals for forced-feed or pressurized lubrication systems.

If you are trying to solve an oil leak, contact us!

Fixing these leaks can save your plant a lot of money. The cost of the leak goes beyond the price of the oil lost. Oil leaks cost money to clean up, waste oil needs to be disposed of, and reservoir levels need to be monitored. Some leaks are only controlled with a large volume continuous nitrogen purge which costs money. Leaks on the high-pressure end of a steam turbine can create a fire hazard with quite critical implications.

Why do bearing case seals leak?

The bearing case seal on a rotating machine is often an overlooked component. Particularly with older machines, the designs are usually a basic labyrinth with a few large teeth. Before we get to the weaknesses in many of these designs, it is important to find the cause of the oil leak.

To find the root cause of the leak, it is important to examine not only the seal, but also the bearing case design and lube system.

  • Seal leaks can be induced at installation—did the mechanic scrape too much clearance at installation or use excessive sealing compound at the split line?
  • The bearing case needs to be properly vented to allow a free flow of oil out and back to the reservoir–plugged vents, no venting, or improper venting of the bearing case can cause leaks.
  • Did a bearing change? Chamfers or v-notches at ends of axial oil distribution grooves can oversupply the bearing. Alternatively, oil can be directed so that squirting oil is sneaking past the oil seal.
  • Oil supply to tilt-pad bearings—does the design have a good end seal to direct oil towards drain?
  • Is the leak coming from the oil supply lines?
  • Is oil pressure supply higher than design?
  • Was new instrumentation installed? Could a fitting be the source of the leak?
  • High velocity windage from coupling or step design—creating localized low pressure that tends to pull the oil out of the bearing housing. Was the coupling design changed?

Fully determining the cause during operation can be a challenge. Many components will not be available for inspection, and critical machines are not easy to shut down for troubleshooting. Inspection of spare parts in the warehouse and some logical intuition is required. Did the leak just start? Has something just changed? Or, has the leak been a persistent issue that has simply been “managed” up to this point.

Once you have recognized that the leak has been a persistent issue that has only been managed, then it is time to look at the seal design. For a leak that has been persistent, it would not be surprising to find a nitrogen purge, baffles, or other modifications to the original design.

Time to Redesign the Seal

At this point, it is time to consider a new seal design. Contact Boulden for assistance because our team at GCGS has decades of experience in solving oil leaks.

We will redesign your seal, optimizing several design parameters to eliminate the oil leak. Some of the factors we will look at include:

  • Seal clearance
  • Number of laby teeth
  • Laby tooth height and pitch
  • Use of appropriate baffles
  • Designing purge provisions (if available)
  • Use of generous drain areas
  • Application of a “wind-back” bore
  • Material selection—we can design seals from a wide variety of materials including modern composite plastics.

Optimizing your seal in every aspect possible will give you the best possible seal for your machine.

Information Required

When we design a new seal, we’ll need accurate dimensions of both where the current seal fits and how much additional space is available.

  • How much space is available?
  • Are there any vibration probes that need to be accounted for
  • Accurate shaft diameters
  • Proximity of couplings and steps in shaft diameter
  • Record the drain path for oil leaving the seal
  • Note any purge availability
  • Outside diameter profile of current seal to ensure fit into bearing housing

With the above details noted, we can propose a custom-manufactured, drop-in replacement for the original seals on your machine.

 

Which Machines?

Oil leaks can occur on any rotating machine with a pressurized, force-feed lubrication system. Pumps, motors, gearboxes, compressors and turbines can all suffer from oil leaks.

Consider some examples:

Steam Turbine at an Ammonia Plant

Motors in a Chemical Plant

Several years ago, the topping turbine at an ammonia plant had major oil leaks. Water hoses were used to continuously flush oil out from under the turbine. It became standard procedure in order to avoid fires. While the typical modifications to the existing seal (i.e. purge lines) had some success in reducing leakage, problems persisted. The OEM seal had several important limitations. There were only a few large labyrinth teeth with several drain holes between the teeth. When the plant added a purge, most likely it simply bypassed to the drain.

The redesigned seal used several changes. A smaller pitch tooth was used, allowing more teeth. The seal was designed so the purge entered the teeth away from the drains. Large drain holes were included where they were most needed. Finally, a wind-back bore was used to increase the effectiveness of the seal when running.

After the new seal was installed, oil leakage was reduced to zero. The purge nitrogen was not even needed. The plant subsequently upgraded the seals on the ammonia compressor and air compressor drivers along with every other machine with an oil leak—no matter how small.

A chemical plant had six identical 2500 hp motors with the same problem. Oil was leaking into the motor, causing electrical problems, even though the bearings were oil ring fed and not pressurized. The main problem on these machines was windage from the motor creating a low-pressure region next to the oil seal, pulling oil out of the bearing case and into the motor windings.

The solution for this customer was a newly designed seal with two separate sealing areas and a nitrogen purge between them. Again, a wind-back bore, optimized tooth design, and more labyrinth teeth were applied. An engineered composite material was used for the teeth so the seal could tolerate transient contact at start-up. All six motors were upgraded and problems with oil leaks were eliminated.

Contact Boulden

If you have a persistent oil leak on a compressor, pump, turbine, gearbox, or motor, contact Boulden. Our approach to this problem is based on decades of experience. We will take a detailed approach to the design, optimizing the seal for your machine to help you eliminate the oil leak.

Furthermore, our solution is simple. Our seals allow you to stick with traditional labyrinth technology with no machinery modifications required. We will do detailed engineering to make sure the seal is a drop-in replacement for your existing components. We know how important your machines are to your operations and will respond as quickly as needed to get you up and running with your problem solved.

If you have a persistent oil leak on a compressor, pump, turbine, gearbox, or motor, contact Boulden. Our approach to this problem is based on decades of experience. We will take a detailed approach to the design, optimizing the seal for your machine to help you eliminate the oil leak.

Furthermore, our solution is simple. Our seals allow you to stick with traditional labyrinth technology with no machinery modifications required. We will do detailed engineering to make sure the seal is a drop-in replacement for your existing components. We know how important your machines are to your operations and will respond as quickly as needed to get you up and running with your problem solved.

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