Elimination of Overheating of Hydraulic Systems: Diagnostics with Thermal Imaging Control, Flow and Pressure Analysis

1. Description of the Problem and Scope of Application

Overheating of the hydraulic system is a critical malfunction that significantly reduces the efficiency of the equipment, accelerates the degradation of the hydraulic oil, damages the components and can lead to a complete stoppage of production. This manual is intended for the systematic diagnosis and elimination of malfunctions associated with an excessive increase in the temperature of the hydraulic fluid in UNITEC-D GmbH industrial installations. Applies to a wide range of hydraulic systems including presses, forming machines, lifting mechanisms, metalworking equipment and mobile hydraulics.

• Typical Symptoms: Oil temperature exceeds operating range (typically > 60-70 °C), temperature alarms sound, burnt oil smell, oil discoloration, slow or erratic operation of actuators, increased noise, reduced life of seals and hoses.
• Severity Classification: Hydraulic system overheating is always classified as a critical fault requiring immediate diagnosis and rectification to prevent cascading damage and significant financial loss.

2. Safety Precautions and Techniques

WARNING: Working with hydraulic systems involves high pressure, high temperature and hazardous substances. Failure to follow safety instructions can result in serious injury or death.

• Lockout and Tagout (LOTO): Before starting any diagnostic or repair work, ensure that the hydraulic system is completely de-energized and all power sources are locked out according to LOTO (Lockout/Tagout) procedures. Check the absence of voltage and pressure.
• Relieving Residual Pressure: Make sure all residual pressure in the hydraulic system is relieved before disconnecting any hoses or components. Use pressure gauges to confirm zero pressure.
• Protective Equipment (PPE): Always use appropriate PPE: safety glasses or shield, gloves (resistant to oil and high temperatures), protective clothing, safety shoes.
• Hot Fluids and Surfaces: Hydraulic oil can reach very high temperatures. Be careful to avoid burns. System components can also be hot.
• Oil Spills: Prepare absorbent materials for immediate cleanup of oil spills to prevent slippage and environmental contamination.
• Hazardous Conditions: Avoid working in high humidity conditions or in the presence of flammable materials without proper permits and safety precautions.

3. Necessary Diagnostic Tools

The following set of tools is required for effective diagnostics of hydraulic system overheating:

4. Initial Evaluation Checklist

Before starting a detailed diagnosis, perform a visual inspection and collect information:

5. Systematic Diagnostic Algorithm

Diagnostics of overheating of the hydraulic system should be carried out sequentially:

1. Overheat Confirmation and Initial Inspection
   1. Symptom: The oil temperature in the tank exceeds the set maximum (eg > 60-70 °C).
   2. Diagnosis: Use UNITEC-D TempSense IR-50 IR Thermometer or UNITEC-D ProTherm TC-200 Thermal Imaging Camera to confirm oil temperature and identify hot spots on components.
   3. Actions: Record the temperature of the tank, pump, valves, cooler, hoses.
   4. If the temperature is normal, but the alarm is triggered: Check the oil temperature sensor (sensor or wiring malfunction).
2. Cooling System Check
   1. Symptom: High oil temperature, while the cooler does not feel colder at the outlet.
   2. Diagnosis (Air Cooler):
      • Check 1: Visually inspect the radiator for contamination (dust, dirt, oil) and fin damage.
      • If dirty: Flush the radiator with compressed air or special solutions.
      • Check 2: Check the operation of the fan (rotation, direction of air flow, presence of extraneous noises). Measure the fan motor current with a UNITEC-D MultiTest DM-300 multimeter (norm for a 0.75 kW motor: ~1.8-2.2 A at 400V).
      • If the fan does not work or works inefficiently: Check the power supply, motor, blades.
   3. Diagnosis (Water/Liquid Cooler):
      • Check 1: Check for presence and pressure of coolant. Check the supply and drain valves.
      • Check 2: Measure the water temperature at the cooler inlet and outlet with an IR thermometer. The temperature difference ΔT must be appreciable (depending on the design, typically ≥5 °C).
      • If ΔT is small or absent: Possible clogging of cooler channels (scale, deposits). Consider dry cleaning or mechanical cleaning.
   4. Diagnosis (General Cooler):
      • Check 3: Measure the pressure drop across the cooler using UNITEC-D PressureKit PK-600 pressure gauges. A high pressure drop (> 0.5-1 bar) may indicate internal clogging.
3. Hydraulic Pump Check
   1. Symptom: High oil temperature, reduced drive speed, increased pump noise.
   2. Diagnosis:
   • Check 1: Using the UNITEC-D FlowMaster HF-100 flow meter, measure the actual pump flow at nominal pressure. Compare with the passport data of the pump. A flow reduction of > 10-15% indicates internal leakage (wear).
   • Check 2: Measure the temperature of the pump housing with a thermal imaging camera. Localized overheating (> 80-90 °C) indicates excessive internal leakage or bearing failure.
   • Check 3: Check the pressure in the suction line (vacuum) using a special vacuum gauge. High vacuum (< -0.2 bar) indicates a clogged suction filter or a problem with the suction line.
4. Hydraulic Oil Check
   1. Symptom: Burning smell, darkening, turbidity of oil, accelerated wear of components.
   2. Diagnosis:
      • Check 1: Take an oil sample for analysis. Use the UNITEC-D OilCheck Express Kit for rapid determination of viscosity, water and solids.
      • If the viscosity is reduced: Thermal degradation of the oil.
      • If the water content is high (> 0.1%): Reduces lubricating properties, causes corrosion, forms emulsions that contribute to overheating.
      • If the content of solid particles is high: Wear of the pump and valves, clogging of filters and cooler.
      • Check 2: Schedule a full lab analysis of the oil (according to ISO 4406 for purity).
5. Checking Valves and Control System
   1. Symptom: Local overheating of valves, pressure drop, unstable operation of actuators.
   2. Diagnosis (Relief Valve):
      • Check 1: Measure the temperature of the relief valve body with a thermal imaging camera. Visible overheating of the valve at normal operating pressure indicates permanent operation (leakage through the valve).
      • Check 2: Check the valve actuation pressure setting with a pressure gauge. If the valve operates at a pressure below the set point, it can continuously dump oil into the tank, generating heat.
   3. Diagnosis (Pressure Regulator):
      • Check 1: Check actual system pressure using UNITEC-D PressureKit PK-600 manometers. Compare with the given. Unstable pressure or constantly high pressure can cause overheating.
   4. Diagnosis (Throttle and Guide Valves):
      • Check 1: Measure the pressure drop across the valves. A high pressure drop at normal flow may indicate excessive resistance generating heat.
      • Check 2: Check the condition of the valve spools (sticking, wear). Sticking of spools leads to restriction of flow and heating.
6. Check System Size and Operating Parameters
   1. Symptom: Overheating occurs from the moment of commissioning or after changing duty cycles/loads.
   2. Diagnosis: See project documentation. Check if the size of the cooler corresponds to the heat load of the system (measure the heat output of the system).
   3. If the system is not cooling enough: Perhaps the cooler is too small for the current operating conditions, or the system is operating in modes for which it was not designed.

6. Matrix of Malfunctions and Causes

7. Analysis of the Root Causes of Each Malfunction

7.1. Malfunction of the Cooling System

• Explanation: The cooler (radiator) is a key component for removing excess heat. Its clogging, fan/pump malfunction, or coolant flow restriction leads to reduced heat output. Clogging of the outer fins of the radiator with dust and dirt (especially in metalworking or woodworking conditions) is the most common cause. Internal clogging (scale in water coolers) reduces the heat exchange area.
• Confirmation: Low temperature difference between oil inlet and outlet of the cooler (ΔT < 5 °C), high oil temperature in the tank, while the cooler itself is not as hot as it should be. Reduced fan airflow or no water circulation. High pressure drop on the cooler (> 0.5-1 bar).
• Damage if not removed: Accelerated degradation of oil, which leads to wear of all components of the hydraulic system (pumps, valves, cylinders). Constant temperature crashes and shutdowns.

7.2. Internal Wear of the Hydraulic Pump

• Explanation: Over time, due to friction and oil contamination, the internal components of the pump (pistons, vanes, gears, bearings) wear out. This leads to an increase in internal leakage between the pressure and suction sides. The energy that must be transferred to the working fluid is converted into heat inside the pump, raising the temperature of the oil.
• Confirmation: Reduction of volumetric efficiency of the pump (the measured flow is much lower than the calculated one at the given pressure), increased temperature of the pump body (> 80-90 °C), increased noise, pressure pulsations, slow response of the drives.
• Damage if not removed: Complete failure of the pump, contamination of the entire system with metallic wear particles, causing damage to other components.

7.3. Malfunction or Improper Adjustment of Relief Valve

• Explanation: The relief valve is designed to protect the system from excess pressure by draining the oil back into the tank. If the valve is constantly actuated due to improper adjustment (actuation pressure too low), or if it is stuck in the open/partially open position, a significant portion of the oil flow is constantly passing through it, converting kinetic energy into heat.
• Confirmation: Local overheating of the safety valve body (> 80 °C), constant noise or vibration from the valve, indicating constant flow through it, reduced pressure in the system under load.
• Damage if not eliminated: Uncontrolled heating of the oil, loss of power, impossibility of reaching the required operating pressure, accelerated wear of the oil.

7.4. Degradation or Contamination of Hydraulic Oil

• Explanation: Hydraulic oil has a limited service life. It degrades under the influence of high temperatures, water, air and pollution. Its viscosity decreases (which leads to an increase in internal leaks), its lubricating and anti-wear properties are lost, deposits and sludge are formed. Dirty oil increases friction, wears out components and clogs filters and coolers.
• Confirmation: Change in oil color (darkening, turbidity), burnt or sour smell, decrease in viscosity, high content of water or solid particles (according to ISO 4406 analysis).
• Damage if not removed: Significant acceleration of wear of all hydraulic components, complete failure of the system, need for expensive repair or replacement of equipment.

7.5. Insufficient System Size or Operation outside Design Parameters

• Explanation: If a hydraulic system (especially a cooler) was designed for one condition, but is operated under significantly higher loads, higher speeds, or in conditions of increased ambient temperature, it can overheat due to insufficient heat transfer. Also, too small volume of the hydraulic tank leads to rapid heating of the entire volume of oil.
• Confirmation: Overheating is observed from the moment of commissioning or after changing the technological process/load. Analysis of the project documentation and calculation of the heat balance shows insufficient capacity of the cooler or a small volume of the tank.
• Damage if Not Remedied: Constant overheating and all its consequences, with no possibility of elimination without modification or redesign of the system.

8. Step-by-Step Troubleshooting Procedures

BEFORE BEGINNING ANY REPAIR WORK, BE SURE TO PERFORM LOTO AND RELIEF OF RESIDUAL PRESSURE!

8.1. Cooling System Troubleshooting

1. Cleaning the Air Cooler:
   1. De-energize the system (LOTO).
   2. Using compressed air (max. 6 bar) and a soft brush, remove dust, dirt, oil from the radiator fins. Work from the opposite side of the normal air flow.
   3. Check for damage to the ribs. Align them as needed.
2. Cooler Fan/Pump Check:
   1. Check fan rotation and flow direction (for air coolers).
   2. Measure the fan motor current. Compare with passport data. Replace the motor/fan if the current is significantly different or if the fan does not work.
   3. For water coolers, check the water circulation pump and clean the water line filter.
3. Cleaning the Water Cooler:
   1. Relieve the pressure and drain the oil and water from the cooler.
   2. Flush the cooler with a chemical descaling solution (such as a citric acid solution) according to the manufacturer's instructions.
   3. Rinse thoroughly with water and dry before refilling.

8.2. Hydraulic Pump Repair/Replacement

1. Diagnostics of Pump Wear:
   1. Connect the UNITEC-D FlowMaster HF-100 flow meter to the discharge line.
   2. Bring the system to the rated operating pressure. Capture the actual flow.
   3. If the flow is less than 85% of the rated value, the pump has a significant internal leak.
2. Repair/Replacement:
   1. De-energize system (LOTO), release pressure.
   2. Disconnect the pump from the electric motor and hydraulic lines.
   3. Carry out repairs (replacement of seals, bearings, internal elements according to the manufacturer's instructions) or complete replacement of the pump with a new one (UNITEC-D recommends pumps from the UNITEC-D E-Catalog, suitable for performance and pressure).
   4. After installing the new/refurbished pump, check the alignment of the shafts (tolerance < 0.05 mm) and tighten the fasteners according to the tightening torque (eg M12 class 8.8: 80 Nm).

8.3. Safety Valve Adjustment/Repair

1. Check and Adjust:
   1. Connect the UNITEC-D PressureKit PK-600 pressure gauge to the line before the relief valve.
   2. Gradually increase the pressure, watching the pressure gauge.
   3. Adjust the relief valve to the specified operating pressure of the system (for example, 10-15% above the maximum operating pressure, but not above the tolerance for the weakest component).
2. Repair/Replacement:
   1. If the valve is stuck or does not hold pressure even after adjustment, de-energize the system (LOTO), release the pressure.
   2. Dismantle the valve, disassemble, inspect for damage, clogging, wear of springs, seat, spool.
   3. Clean or replace defective parts. Install a new valve (UNITEC-D offers a wide range of CE and UkrSEPRO certified valves).

8.4. Replacement or Filtration of Hydraulic Oil

1. Analysis and Solution:
   1. If the oil analysis shows degradation, contamination or high water content, replace the oil completely.
   2. If the oil is relatively new but has a high solids content, off-cycle fine filtration may be considered.
2. Replacement procedure:
   1. De-energize the system (LOTO), release pressure.
   2. Drain all old oil from tank, lines, cylinders and components.
   3. Flush the tank and, if possible, the system with flushing oil.
   4. Replace all hydraulic filters (suction, pressure, drain) with new ones according to the UNITEC-D specification.
   5. Fill the system with new, clean hydraulic oil recommended by the equipment manufacturer and suitable for the climatic conditions (e.g. ISO VG 46 for general industrial use at +20...+40 °C). Use a fill pump with a filter (< 10 µm).

8.5. Modernization of the Cooling System or Pump

1. Consultation and Design:
   1. If all other causes are ruled out and overheating persists, contact UNITEC-D engineers to recalculate the thermal balance of the system.
   2. Consider installing a larger capacity chiller or aftercooler.
   3. Evaluate the feasibility of installing a variable displacement pump or an energy-efficient motor.

9. Precautions and Prevention

10. UNITEC-D Spare Parts and Components

For quick and efficient repairs, it is recommended to have the following spare parts available:

All necessary components are available in our electronic catalog: www.unitecd.com/e-catalog/

11. Links

• DSTU ISO 4406:1999 Volumetric hydraulics. Hydraulic fluids. A method of determining the level of pollution by solid particles.
• EN ISO 11158:2023 Lubricants, industrial oils and related products (class L). Classification. Group H (hydraulic systems).
• ISO 2941, ISO 2942, ISO 2943: Standards for hydraulic filters.
• Instructions for operation and maintenance of UNITEC-D GmbH equipment.
• UNITEC-D: Manual for Hydraulic Oil Analysis (internal document).