×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

Centrifugal Compressor Thrust Bearing Jacking Oil

Centrifugal Compressor Thrust Bearing Jacking Oil

Centrifugal Compressor Thrust Bearing Jacking Oil

(OP)
Working on an overhung centrifugal compressor, and come to find out the OEM has a "jacking oil" system (giggity), which feeds high pressure (2000 psi), low volume ( 0.5 gpm) lube oil to, what looks to be just one side of the thrust bearing, and only during start-up and shutdown.

We have a couple different other brands of overhung compressors which are quite mechanically similar to this one, and they have just normal lube oil supply at pressures less than 100 psi.

The only thing I can figure is that with out the aid of a balance piston in the overhung design, that the high pressure oil is there to supplement the oil film at low shaft speeds until such speed is reached that the hydrodynamic oil film can develop with normal oil supply conditions.

However none of the other designs has this system, and am wondering if this most likely a knee-jerk design consideration after a incidident involving or due to a failed thrust bearing.

Anyone have any real knowledge about why such a system may have been put in service?

RE: Centrifugal Compressor Thrust Bearing Jacking Oil

None of our overhung machines have this feature.  But, all of ours run with relatively low suction pressure. If your machine has a high suction pressure, then the thrust load on the inactive thrust bearing could be quite high until the rotor builds pressure and begins normal thrust.  Keep in mind, I am not referring to a high compressor differential pressure.  All that matters is suction pressure acting over the area of the seal.  A net thrust is produced that thrusts away from the impeller. If this thrust is high, then the breakaway torque to get the machine spinning might be too high for the driver. This could be especially true if the driver is a synchronous motor which has limited breakaway torque.  But, without more details about you machine, driver, and process conditions, this is just speculation.

Johnny Pellin

RE: Centrifugal Compressor Thrust Bearing Jacking Oil

(OP)
Details of this particular machine:

22,000 hp, VFD driven synchronous motor, 1800 rpm, with speed increasing gear box, with compressor speeds up to about 8300 rpm.

process conditions are generally 500 to 600 psig suction pressure, and 700 to 800 pisg discharge pressure, with 0.6 SG natural gas.

We have several other machines by two other manufactures, which are very similar to this one and operate at pretty much the same process conditions, and none of them have this jacking oil system either.  

Whatever the reason, we're going to re-install and re-use this system.

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources