Troubleshooting Lube Oil Units: 5 Fixes for Low Pressure and High Temperature Issues

Lubrication oil systems are the lifeblood of rotating equipment in power generation, petrochemical processing, and manufacturing facilities. When these systems experience issues like low pressure or high temperatures, the consequences can be severe—ranging from reduced efficiency to catastrophic equipment failure. According to industry data, approximately 43% of turbomachinery failures can be traced back to lubrication system problems, making proper troubleshooting and maintenance essential for operational reliability.

Lube oil units serve multiple critical functions beyond simple lubrication, including heat removal, contaminant flushing, corrosion prevention, and in many cases, hydraulic control actuation. The system typically consists of main and auxiliary pumps, heat exchangers, filters, instrumentation, and control valves—each component presenting potential failure points that could manifest as pressure or temperature issues.

At HTAC, our engineering team has observed that addressing these problems requires a systematic approach. With over four decades of experience designing and manufacturing lube oil consoles for nearly 3,000 turbomachines globally, we've identified the most effective troubleshooting methods for common lubrication system problems.

Pump-Related Problems

Low oil pressure frequently originates from pump-related issues. The main oil pump typically provides the primary motive force for the entire lubrication system, making its performance critical for maintaining proper pressure throughout the circuit. When investigating pump problems, consider these potential causes:

Pump cavitation occurs when the available Net Positive Suction Head (NPSH) falls below the required level. This creates vapor bubbles that collapse violently inside the pump, causing noise, vibration, and reduced flow. Check for:

Clogged suction strainers

Low oil level in the reservoir

Excessively high oil viscosity during cold starts

Air leaks in the suction line

Pump wear or damage gradually reduces performance over time. Bearings, impellers, or rotors can deteriorate due to normal operation or accelerated damage from contamination. Internal recirculation resulting from worn clearances reduces net output pressure. Consider:

"Clearance increases of just 0.1mm in critical pump components can reduce volumetric efficiency by up to 15%, directly impacting system pressure." — Turbomachinery International

Control issues may affect pump speed in variable-speed applications or bypass flow in fixed-speed setups. Check for:

Failed speed sensors

Malfunctioning speed controllers

Stuck pressure control valves

Faulty pressure transducers providing incorrect feedback

Addressing pump issues typically requires careful inspection and potentially disassembly by qualified personnel. For critical applications, implementing condition monitoring with vibration analysis and performance trending can help identify developing problems before they cause operational disruptions.

Heat Exchanger Issues

Elevated oil temperatures often indicate problems with the oil cooler or heat exchanger. These components are designed to remove heat generated by mechanical losses in the turbomachinery and maintain oil temperature within the optimal operating range. Several factors can reduce heat exchanger efficiency:

Fouling on the cooling medium side restricts flow and reduces the heat transfer coefficient. This commonly occurs in water-cooled systems where mineral deposits, biological growth, or suspended solids can accumulate on heat transfer surfaces. Signs include:

Gradually increasing oil temperature over time

Reduced cooling water flow

Increased pressure drop across the cooling water circuit

Oil-side fouling from oxidation products, additive breakdown, or external contamination can create an insulating layer on heat transfer surfaces. This is particularly common in high-temperature applications or when oil quality deterioration has occurred. Regular oil analysis can help identify this condition before it significantly impacts cooling performance.

Inadequate cooling medium supply may result from:

Potential Cause Verification Method Typical Solution

Low cooling water pressure Check supply pressure against design Adjust upstream pressure control

Insufficient cooling water flow Verify flow rates at exchanger Clear restrictions, adjust balancing valves

Elevated cooling water temperature Compare inlet temperature to specifications Address upstream cooling tower issues

Air-cooler fan malfunction Check fan operation and air flow Repair/replace fan motor or controller

Regular performance monitoring of heat exchangers allows for early detection of developing problems. Tracking the approach temperature (the difference between oil outlet temperature and cooling medium inlet temperature) provides a reliable indicator of heat exchanger efficiency regardless of load conditions.

Filter Clogging

Filtration systems play a crucial role in maintaining oil cleanliness and protecting turbomachinery components. However, excessive pressure drop across filters can trigger bypass operation, allowing unfiltered oil to circulate through the system. This not only accelerates wear in the equipment but can also manifest as low pressure at critical lubrication points.

Identifying filter bypass operation:

Unexpected improvement in differential pressure without filter change

High particle counts in oil analysis despite recent filter installation

Visible actuation of mechanical bypass indicators

Filter differential pressure at or exceeding bypass setpoint

Causes of accelerated filter clogging include:

External contamination from inadequate reservoir breathers, poor maintenance practices, or seal failures

Internal contamination from equipment wear, oil degradation, or chemical incompatibility

Water contamination leading to oil oxidation and formation of insoluble compounds

Microbial growth in systems with water contamination, particularly during extended shutdowns

Best practices for addressing filtration issues:

Implement a proactive filtration maintenance strategy based on differential pressure monitoring rather than fixed time intervals. This approach optimizes filter life while ensuring continuous protection. Additionally, consider supplementary filtration methods like kidney-loop systems for polishing oil during normal operation.

Bold recommendation: When replacing clogged filters, always investigate the root cause of accelerated clogging rather than simply installing new elements. Address the contamination source to prevent recurrence and extend filter service life.

Oil Degradation

Oil degradation can manifest as both pressure and temperature problems in lubrication systems. As oil ages or becomes contaminated, its viscosity characteristics often change, affecting its flow behavior and heat transfer properties.

Viscosity increase typically results from:

Oxidation due to high temperatures or catalytic metals

Water contamination and resulting emulsions

External contaminants like dust or process materials

Additive depletion or precipitation

Higher viscosity increases pumping power requirements and pressure drops throughout the system, potentially causing low pressure at critical points despite normal pump operation. It also reduces heat transfer efficiency in coolers, leading to elevated operating temperatures.

Viscosity decrease can occur from:

Thermal cracking of the oil molecules

Fuel or solvent contamination

Shear thinning in high-stress applications

Improper oil selection or mixing

Lower viscosity reduces the oil film thickness in bearings and other lubricated interfaces, potentially leading to metal-to-metal contact and accelerated wear. It may also cause internal leakage in pumps and control valves, reducing system pressure.

Regular oil analysis is essential for monitoring these conditions. Key parameters to track include:

Viscosity at 40°C and 100°C

Total Acid Number (TAN)

Water content

Particle count and distribution

Spectrometric analysis for wear metals

As a general guideline, consider oil replacement when viscosity changes exceed 10% from the original specification or when TAN increases by more than 2.0 mg KOH/g from the baseline value. However, always consult the turbomachinery manufacturer's recommendations for specific limits.

Instrumentation Failures

Modern lube oil systems incorporate sophisticated controls and instrumentation to maintain optimal operating conditions. Failures in these components can cause apparent pressure or temperature problems even when the physical equipment is functioning properly.

Pressure transmitter failures may indicate low pressure when actual conditions are normal. Common issues include:

Sensor drift requiring recalibration

Clogged impulse lines

Electronic component failure

Incorrect scaling in the control system

Temperature measurement errors similarly create false indications of system problems. Check for:

Thermowell fouling insulating the sensor

Broken or degraded sensors

Loose connections causing intermittent readings

Ground faults in signal wiring

Control valve malfunctions can prevent proper system regulation. Issues include:

Stuck valve mechanisms from contamination or mechanical damage

Actuator failures

Solenoid problems in electro-hydraulic systems

Control signal interruptions

Addressing control system issues:

Implement regular calibration of critical instruments

Verify actual conditions with independent measurements when anomalies appear

Use trend data to identify gradual drift versus sudden failures

Consider redundant instrumentation for critical parameters

For digital control systems, ensure proper software backup and version control to prevent issues during system updates. Document all setpoint changes to maintain a clear record of system configuration.

Systematic Troubleshooting

Effective troubleshooting of lube oil systems requires a methodical approach that considers the interactions between components. Low pressure and high temperature conditions rarely have a single cause, and addressing only the most obvious issue may provide only temporary relief.

HTAC recommends developing a site-specific troubleshooting guide that incorporates the equipment manufacturer's documentation, historical performance data, and operational experience. This resource should include normal operating parameters, alarm thresholds, and step-by-step procedures for investigating common problems.

By implementing proper monitoring, regular maintenance, and proactive troubleshooting of lube oil systems, facilities can significantly improve turbomachinery reliability and performance. For complex issues or system optimization, consider consulting with specialists who have extensive experience with similar installations.

For more information about optimizing your turbomachinery lubrication systems or to discuss specific challenges you're experiencing, contact HTAC's technical support team at mkt_htac@htc.net.cn or +86 571-857-81633. With over four decades of experience designing and manufacturing lubrication systems for nearly 3,000 turbomachines worldwide, our engineers can provide tailored solutions to your most challenging lubrication problems.