A centrifugal hydrogen recycle compressor is operating at 17 kg/cm2g suction pressure and 21 kg/cm2g discharge pressure. The reported symptom is a seal-oil reservoir gain of approximately 70 L/h accompanied by an equivalent lube-oil reservoir loss. That matching inventory change supports internal or external oil transfer, but the available evidence does not identify a single confirmed path.
Establish the Oil Balance
Trend both reservoir levels over the same stable operating interval and convert each level change to volume using the correct vessel geometry. Confirm that seal-oil gain approximately equals lube-oil loss after accounting for oil additions, drains, sampling, leakage, and level-measurement error. A repeatable balance strengthens the transfer diagnosis; a mismatch indicates another inventory path or an inaccurate level calculation.
Evaluate the Supported Transfer Paths
| Possible path or cause | Mechanism | Required check |
|---|---|---|
| Leaking crossover valve | A connection between the reservoirs can pass oil when the lube-oil reservoir is at the higher hydraulic level or pressure. | Trace the P&ID, walk down every crossover, and test valve isolation. |
| Restricted lube-oil return | Return oil can back up and cross the separation seal into the clean seal-oil return. | Inspect the return line and drain passages for restriction. |
| Blocked lube-oil reservoir vent | Reservoir pressurization can impair drainage and drive oil toward the seal area. | Verify that the vent path is open and correctly arranged. |
| Blocked seal-oil drain-cavity breather | Vacuum in the cavity can draw lube oil across the separation seal. | Inspect the breather and check the cavity pressure condition. |
| Missing or incorrect supply orifice | Excessive lube-oil flow can overwhelm the drain system. | Compare installed orifices with the approved drawing, especially after maintenance. |
| Excessive lube-oil supply pressure | A pressure-control fault can increase flow beyond drain capacity. | Measure supply pressure and verify controller operation against approved settings. |
| Increased bushing clearance | If buffered-oil bushing seals are installed, leakage can increase as shaft-to-bushing clearance increases. | Confirm the seal design from the cross-section and inspect clearances using manufacturer criteria. |
Run a Focused Diagnostic Procedure
- Review the current P&ID and compressor seal cross-section to identify every intentional connection among the lube-oil reservoir, seal-oil reservoir, returns, vents, drain cavities, and overhead or rundown tank.
- Walk down the installed piping against the drawings. Check crossover-valve tightness before disturbing compressor internals.
- Inspect lube-oil returns, reservoir vents, and seal drain-cavity breathers for restrictions or incorrect valve alignment.
- Measure lube-oil supply pressure and confirm pressure-controller stability. Do not substitute an assumed setpoint; use the approved equipment documentation.
- If maintenance preceded the level change, verify that every lube-oil supply orifice was reinstalled in the correct location and orientation.
- If external piping, venting, drainage, pressure, and orifice checks pass, inspect the separation or bushing seal using the compressor cross-section and manufacturer limits.
Verify the Corrective Action
After correcting a confirmed defect, operate under a comparable condition and repeat the synchronized reservoir balance. The transfer is controlled only when the approximately 70 L/h opposing trend disappears without creating poor seal-oil differential pressure, inadequate lubrication, abnormal drain behavior, or process contamination. The evidence states that buffered-oil pressure must remain above sealing pressure if bushing seals are used, but it does not provide the required differential, seal geometry, shaft size, clearances, or controller setpoint; obtain those values from the compressor documentation before changing pressure.
FAQ
Why does my seal-oil reservoir rise while the lube-oil reservoir falls?
Matching gain and loss indicate a likely transfer path. Check crossover valves, restricted returns, blocked vents, excessive supply pressure, missing orifices, and the separation seal.
Can a blocked lube-oil vent send oil into the seal system?
Yes. Reservoir pressurization can impair drainage and promote leakage toward the seal area, so verify the complete vent arrangement and confirm that each path is open.
What should I check first for a 70 L/h oil transfer?
First confirm the synchronized volume balance, then trace the P&ID and field piping for crossover connections and leaking isolation valves. Next inspect returns, vents, supply pressure, and installed orifices before opening the compressor.