1. Scope of Application and Purpose
This maintenance manual is intended for qualified technicians, service engineers and those responsible for the reliability of production equipment in industrial environments. It covers the procedure for flushing hydraulic systems, which is a critical operation to remove contaminants, replace filter elements and take oil samples for analysis. Contamination of hydraulic oil is a major cause of component failure, resulting in equipment downtime, reduced efficiency, and increased operating costs.
The purpose of this manual is to provide clear, step-by-step instructions for effectively cleaning hydraulic systems, restoring optimal oil purity, and ensuring long-term reliability of hydraulic equipment. Flushing the system is mandatory when:
- Commissioning of a new hydraulic system.
- After overhaul or replacement of the main hydraulic components (pumps, valves, cylinders).
- When significant contamination of the oil is detected according to the results of the analysis (for example, exceeding the target purity class ISO 4406).
- To extend the life of hydraulic oil and components.
- When switching to another type of hydraulic oil.
Adherence to this procedure will ensure that the system meets the cleanliness standards that are the foundation for the stable and efficient operation of production equipment.
2. Security measures
IMPORTANT: Before beginning any work on the hydraulic system, be sure to read the equipment operator's manual and follow all factory instructions and local safety regulations. Failure to follow these precautions could result in serious injury or death.
- Lockout/Tagout: Before opening the hydraulic system, perform a lockout/tagout procedure according to ISO 14118 and internal company rules. Make sure all power sources (electrical, hydraulic, pneumatic) are de-energized and locked out. Check for voltage and residual pressure.
- Disposing of residual pressure:Hydraulic systems can maintain high pressure even after the pump is turned off. Slowly and in a controlled manner, release all residual pressure in the system using the appropriate valves or procedures specified in the equipment manual. Make sure the pressure gauges are at zero pressure before removing any components.
- Personal protective equipment (PPE):
- Eye protection: Always use safety glasses or a shield according to EN 166.
- Hand protection: Use oil-resistant protective gloves (e.g. nitrile) according to EN ISO 374-1.
- Body protection: Wear protective clothing against oil splashes.
- Foot protection: Use safety shoes with oil-resistant soles and metal toes (EN ISO 20345).
- Respiratory protection: If there is a risk of inhaling hydraulic oil vapors, use appropriate respirators.
- Hot surfaces and liquids:Hydraulic oil can reach high temperatures during operation. BE CAREFUL to avoid burns. Always allow the system to cool down to a safe temperature (<40°C) before starting work if possible.
- Oil Spills: Hydraulic oil is slippery and can cause falls. Clean up any spills immediately. Use absorbent materials.
- Lifting operations: When working with heavy components, use appropriate lifting equipment and follow the rules for safe lifting of loads.
- Environmental responsibility: Collect used hydraulic oil and filter elements in sealed containers for proper disposal in accordance with local environmental regulations. DO NOT POUR OIL INTO SEWERS OR ON THE GROUND.
3. Necessary Tools and Materials
| Name of Tool/Material | Specification | Quantity |
|---|---|---|
| Wrench/socket set | Metric, from 8 mm to 36 mm | 1 set |
| Torque wrench | Range 10-200 Nm, accuracy ±3% (according to ISO 6789) | 1 pc. |
| Pump installation for flushing hydraulics | Performance 50-150 l/min, with fine filter (eg 3 μm Beta(c) ≥ 200) and low pressure pump | 1 pc. |
| Hydraulic hoses with quick disconnect connections | Length 3-5 m, DN25 (1"), PN up to 250 bar, resistant to hydraulic oil | 4 pcs. |
| Adapters and plugs | Appropriate hydraulic system port sizes (eg G1/2, G3/4, G1, M18x1.5, M22x1.5) | 1 set |
| Flow meter | Range 10-200 l/min, accuracy ±1.5% | 1 pc. |
| Manometers | Range 0-10 bar and 0-250 bar, accuracy class 1.0 (for pressure control on filters and in the system) | 2 pcs. |
| Thermometer | Range 0-100°C, accuracy ±1°C | 1 pc. |
| Oil purity monitoring system (portable particle counter) | Ability to measure purity grade as of ISO 4406 (eg 18/16/13) | 1 pc. (or laboratory services) |
| Containers for draining used oil | Volume sufficient for the full volume of the system | 2-3 pcs. |
| New hydraulic oil | The type and viscosity recommended by the equipment manufacturer, the cleanliness class of refueling is not worse than ISO 17/15/12 | The corresponding volume of the system + 10-20% for washing |
| Filter elements for washing | High-performance filters (3-5 μm absolute) for the washing unit and for the main system | According to the number of filters in the system + 2-3 spare sets |
| Absorbent materials and rags | Industrial, lint-free | It's enough |
| Washing liquid (if needed) | Specialized flushing fluid compatible with system components and seals (only as recommended by the equipment manufacturer) | Appropriate volume |
| Oil sampling kit | Vacuum pump, sterile sample bottles (100-250 ml), identification labels | 1 set |
| Marking tags and locking devices (LOTO) | According to company standards | It's enough |
4. Checklist Before Washing
Before starting a hydraulic flushing procedure, perform a thorough inspection to identify potential problems and ensure the job is completed safely and efficiently.
| Element | Verification | Acceptance/Rejection Criteria | Notes |
|---|---|---|---|
| Equipment condition | Visual inspection of the hydraulic system for leaks, damage to hoses, pipelines, seals. | Absence of visible leaks, cracks, deformations. Hoses and pipes are securely fastened. | Record any defects found and eliminate them before starting the wash. |
| Oil level in the tank | Checking the oil level using a dipstick or dipstick. | The level is within the permissible limits (minimum/maximum). | Insufficient level can cause pump cavitation during flushing. |
| Manometers and thermometers | Checking the performance and calibration of installed manometers and thermometers. | The devices show reliable values, there are no mechanical damages. | Ensure availability of proven parameters control devices. |
| System filters | Visual inspection of filter contamination indicators (if any) or replacement history. | Pollution indicators do not show a critical level. Filters were replaced according to the schedule. | Prepare new filter elements in advance for replacement after washing. |
| Availability of documentation | Availability of basic hydraulic diagrams, electrical diagrams, operating manuals. | All necessary technical documentation is available. | Vital for understanding the system and identifying connection points. |
| Access to the system | Ensuring free access to all connection points, drain, filters and tank. | The working area is clean, free of obstacles. There is enough space for manipulation of tools and equipment. | Danger of injury or equipment damage in confined spaces. |
| Oil condition (visual) | Visual inspection of the oil in the tank through the sight glass or with the help of a transparent container. | Absence of significant turbidity, water (emulsion), large particles, strong darkening or burning smell. | Significant visual pollution indicates the need for urgent washing. |
| Oil temperature | Control of the current temperature of the hydraulic oil. | The temperature should be within the operating range (>30°C for effective flushing, but <60°C for safety). | Cold oil has a higher viscosity, which makes it difficult to remove impurities. |
5. Step-by-step Procedure
5.1. Preparing the System for Flushing
- System Shutdown and Lockout:
- Turn off the hydraulic station main drive and all associated equipment.
- Perform a lockout/tagout (LOTO) procedure on the main power switch and all potential sources of energy that could activate the hydraulic system. MAKE SURE THE SYSTEM IS COMPLETELY POWER OFF.
- Error: Forgetting to block auxiliary power supplies (eg for coolers or oil heaters).
- Residual Pressure Relief:
- Slowly open all manual pressure relief valves or use controlled cylinder/engine movement (if safe and permitted) to completely relieve residual pressure in accumulators and lines.
- Visually check the pressure gauges. They should show 0 bar.
- Error: Failure to check the pressure in all branches of the system, which can lead to uncontrolled release of oil under pressure.
- Waste Oil Drainage (Partial or Full):
- Place suitable oil collection containers under the hydraulic tank drain points.
- Open the tank drain valve. If possible, also drain the oil from the lowest points of the lines and hydraulic cylinders.
- Assess the amount of drained oil and its visual condition (color, presence of water, particles).
- Close the drain valves after draining.
- Error: Underestimate the volume of oil, which leads to the overflow of collection tanks.
5.2. Installation of the Flushing Circuit
- Washing Installation Connection:
- Determine the connection points of the washing installation. This is usually a drain port to the tank (or special flush port) and a return port from the system to the tank. It is desirable that the flushing liquid circulates through the entire circuit, including lines and actuators.
- Use prepared hydraulic hoses with quick-disconnect connections and adapters for a reliable connection.
- Make sure that all connections are tight, without leaks. Tighten the connections according to the recommended torques. For example, for fittings with a G1/2 thread, the tightening moment can be 40-50 Nm, for G3/4 - 60-70 Nm.
- Mistake: Use hoses of insufficient diameter, which can create excessive resistance and reduce flushing efficiency.
- Installation of Temporary Filters and Bypasses (as required):
- If flushing occurs with circulation through the main components, install additional or thinner temporary filters on the return and/or supply line to protect sensitive components.
- Consider bypassing components that should not be flushed (eg some servo valves, demineralizers).
- Error: Flush through components not designed for flushing fluid or high flow of contaminated oil.
- Filling the System with Flushing Fluid or New Oil:
- Fill the hydraulic tank with new hydraulic oil of the same type that will be used (filling purity class no worse than ISO 17/15/12), or a specialized flushing fluid, if recommended by the equipment manufacturer.
- Provide sufficient liquid level for cavitation-free operation of the scrubber.
- Error: Mixing incompatible hydraulic oils or flushing fluids.
5.3. Flushing the System
- Starting the Flushing Unit:
- Turn on the flushing unit and make sure that the pump runs smoothly, without unusual noises.
- Gradually increase the flow of liquid, controlling the pressure on the filters of the washing unit (usually the working pressure 0.5-2 bar).
- Error: Sudden flush start which can cause hydraulic shock and damage.
- Optimum Temperature Maintenance:
- Warm the hydraulic fluid to operating temperature (40-50°C preferably) to reduce viscosity and increase the effectiveness of removing contaminants. Use the built-in or external heater of the washing unit.
- Monitor the temperature with a thermometer.
- Error: Rinsing with cold oil, which significantly reduces the efficiency of removing sludge and small particles.
- Circulation and Cleanliness Monitoring:
- Ensure continuous circulation of flushing fluid through the entire system. If possible, activate all actuators (cylinders, hydraulic motors) within a safe range to flush all lines.
- Flushing should continue until the target oil purity class of ISO 4406 is reached (eg 16/14/11 or better, depending on the equipment manufacturer's requirements).
- Measure the oil cleanliness grade every 30-60 minutes using a portable particle counter.
- Typical flushing times can range from 4 to 24 hours, depending on the degree of contamination and the volume of the system.
- Visual indicator: The purity of the oil improves, the color becomes more transparent.
- Error: Stopping flushing before target cleanliness class is reached, resulting in rapid recontamination.
- Replacing Filter Elements During Washing:
- Control the pressure drop on the filters of the washing unit. When reaching the maximum recommended drop (for example, 1.5-2 bar), immediately replace the filter elements.
- Error: Ignoring indicators of filter contamination, which leads to their bypassing or destruction and the release of contaminants back into the system.
5.4. Replacement of System Filters
- Stop Flushing and Drainage:
- Turn off the flushing unit.
- Follow the LOTO procedure.
- Relieve system pressure.
- Drain the flushing fluid (if a special fluid was used) or some of the circulating oil from the hydraulic tank into separate containers for disposal. If the flushing was done with working oil, it can be left if the target cleanliness class is reached, but a complete replacement is recommended.
- Replacing the Main Filter Elements:
- Unscrew the filter housings of the main hydraulic system (suction, pressure, drain).
- Remove the old filter elements.
- Thoroughly clean the filter housings from accumulated dirt using lint-free cloths.
- Install new original filter elements recommended by the equipment manufacturer (for example, filter fineness class 10 μm Beta(c) ≥ 200).
- Lubricate the new O-rings with clean hydraulic oil.
- Screw the filter housings. Tightening torques: for cartridge filters 25-35 Nm; for Spin-on threaded filters, tighten by hand, then 1/2 - 3/4 turn with a wrench.
- Error: Installing filter elements of the wrong type or fineness class, which may result in insufficient filtering or flow restriction.
5.5. Selection of an Olive Sample for Analysis
- Preparation for Sampling:
- After washing and changing the filters (and, if necessary, filling with new oil), let the system work in light mode 15-30 minutes to stabilize the parameters.
- Choose an appropriate sampling point: optimally the pressure line after the pump and filter, or a dedicated sampling port that is not a drain point. DO NOT TAKE A SAMPLE FROM THE BOTTOM OF THE TANK.
- Use a sterile collection kit.
- Sampling Procedure:
- Rinse the sampling tap by passing 100-200 ml oil through it, draining it into a separate container for disposal.
- Collect the oil sample in a sterile bottle, filling it approximately 3/4 of the volume.
- Close the bottle tightly.
- Mark the bottle: date, time, name of the equipment, point of selection, type of oil, working hours of the oil (motor hours), presence of filtration/washing.
- Send the sample to an accredited laboratory for comprehensive analysis (purity analysis by ISO 4406, Karl Fischer water content (ISO 12937), viscosity (ISO 3104), infrared spectrum (ASTM D7889) and elemental analysis (ASTM D6595)).
- Error: Taking a sample from an unrepresentative point (for example, from the bottom of a tank) or using non-sterile containers, which will lead to inaccurate analysis results.
5.6. Filling the System with New Oil and Deaeration
- Filling the tank:
- Fill the hydraulic tank with new hydraulic oil that meets the equipment manufacturer's specifications and has the target purity class (eg ISO 17/15/12 or better).
- Always fill the oil through the filler filter (if equipped) or through a flushing unit that has a fine filter to avoid contamination.
- Fill the tank to the manufacturer's recommended level by checking the level indicator.
- Error: Refueling with unfiltered oil directly from the barrel, which can lead to immediate contamination of the system.
- Deaeration of the System (Removal of Air):
- Loosen connections at the highest points of the hydraulic system (eg cylinder pressure lines, valves) or use special valves to remove air.
- Turn the pump on for a short time or pulse, allowing the air to escape.
- Repeat the process until clean oil without air bubbles begins to flow from the drain points.
- Tighten all connections.
- Error: Insufficient air removal, which can lead to cavitation, oil foaming, system instability, and component damage.
5.7. Final Checks and Launch
- Final Leak and Connection Check:
- Visually check all connections, flanges, seals and hoses for leaks.
- Make sure all tools are removed from the work area.
- Error: Forgetting to tighten all connections after disassembly/assembly.
- Starting the System:
- Deactivate LOTO.
- Run the hydraulic system at idle, with no load, for 15-30 minutes.
- Monitor pressure, temperature, noise and vibration.
- Check the operation of all executive mechanisms of the system.
- Error: Run system under full load immediately after maintenance.
- Control of Working Parameters:
- Check the working pressures at different points of the system. They must correspond to the nominal values according to the technical documentation (for example, the working pressure of the pump 160-200 bar, the pressure in the pilot lines 10-15 bar).
- The oil temperature should be within 40-60°C.
- Error: Ignore deviations from normal operating parameters, which may indicate hidden problems.
6. Checklist After Service
After completing the flushing procedure and filling the hydraulic system, perform the following checks to confirm the success of the work and the readiness of the equipment for operation.
| Check | Expected Result | Actual Result | Status (Pass/Fail) |
|---|---|---|---|
| Visual inspection of the sources | Absence of any visible oil leaks on connections, hoses, component housings. | ||
| Oil level in the tank | The oil level is within the limits of the permissible marks on the level indicator. | ||
| Operating pressure of the system | The readings of the manometers correspond to the normative values according to the technical documentation (for example, 160-200 bar for the working pressure). | ||
| Oil temperature | The oil temperature stabilized in the operating range (for example, 40-60°C). | ||
| Absence of unusual noises/vibrations | Smooth operation of the pump and other components without extraneous noises (creaking, pulsation) or excessive vibration. | ||
| Clarity and smooth operation of executive mechanisms | Hydraulic cylinders and hydraulic motors work smoothly, without jerks, delays and excessive speed fluctuations. | ||
| Indication of filter contamination indicators | The contamination indicators of the new filters show "clean" or are in the green sector. | ||
| Results of operational analysis of oil purity (if a portable meter is available) | The oil purity grade of ISO 4406 meets the target values (eg 16/14/11 or better). | ||
| Lack of air in the system (deaeration) | No foaming in the tank, stable oil level, no "soft" reaction of the hydraulic system. | ||
| All blocking and markings have been removed | The LOTO removal procedure is complete, all safety devices are restored. |
7. Troubleshooting Guide
This section provides information on common problems that may occur during or after flushing the hydraulic system, their likely causes, and recommended corrective actions.
| Symptom | Probable Cause | Corrective Action |
|---|---|---|
| After washing, the purity class of the oil does not improve | Insufficient washing time; the filters of the washing unit are dirty or of inappropriate fineness; permanent source of pollution in the system; incomplete circulation of the washing liquid. | Continue washing; replace the filters of the washing unit with new, possibly thinner ones (for example, 3 microns); identify and eliminate the source of pollution; check the flushing circuit for the presence of "dead zones". |
| High pressure drop across the filters (quick contamination) | Excessive initial contamination of the system; too thin filter element for the initial stage; incomplete drainage of old oil. | Install coarse filters at the initial stage of washing, gradually moving to finer ones; perform repeated complete drainage of the system. |
| Unusual pump noise (cavitation) | Low oil level in the tank; air in the system; clogged suction filter; too high oil viscosity (low temperature). | Bring the oil level to normal; deaerate the system; clean/replace the suction filter; increase the oil temperature to working temperature. |
| Unstable or slow operation of executive mechanisms | Air in the system; insufficient pressure; damaged or improperly installed valves; residual contamination blocking channels. | Repeat the deaeration procedure; check pressure settings and operation of safety valves; carry out defect detection of valves; repeat washing. |
| Oil leaks after maintenance | Insufficient tightening of connections; damaged seals or flanges; incorrect installation of components. | Determine the location of the leak; tighten the connection according to the recommended moment; replace damaged seals or flanges; check the correct installation of components. |
| Overheating of hydraulic oil | Insufficient volume of oil; non-working cooler; excessive load on the system; dirty filters; incorrect oil viscosity. | Check the oil level and volume; check the operation of the cooler and its cleanliness; reduce the load or optimize the cycle; replace filters; check compliance of the oil viscosity with the manufacturer's recommendations. |
| Incorrect pressure gauge readings | Malfunction of the manometer; contamination of the connection to the pressure gauge. | Replace the manometer with a new, calibrated one; clear the connection. |
8. Recommended Maintenance Schedule
Maintaining a regular hydraulic maintenance schedule is critical to preventing failures and extending equipment life. The frequency of tasks may vary depending on the intensity of operation, type of equipment and environmental conditions.
| Task | Frequency | Estimated Duration | Qualification Level |
|---|---|---|---|
| Visual inspection of the system (leaks, oil level, temperature) | Daily/Weekly | 10-15 minutes | Operator/Technician (Level 1) |
| Checking the filter contamination indicators | Weekly/Monthly | 5 min | Operator/Technician (Level 1) |
| Oil sample selection for laboratory analysis | Every 500-1000 engine hours or 3-6 months | 20-30 min | Technician (Level 2) |
| Replacement of filter elements (according to the indicators or the schedule) | Every 1000-2000 engine hours or 6-12 months | 30-60 min | Technician (Level 2) |
| Adding oil (filtered) | As necessary, according to the level | 15-30 min | Technician (Level 1) |
| Complete flushing of the hydraulic system (as described in the manual) | Every 5000-10000 engine hours or 2-3 years, or according to the results of the oil analysis. | 4-24 hours (depends on volume and pollution) | Senior Technician/Engineer (Level 3) |
| Changing the hydraulic oil (if flushing is not used or ineffective) | Every 2000-4000 engine hours or 1-2 years, or according to the results of the oil analysis. | 1-4 hours (depends on volume) | Technician (Level 2) |
| Cleaning the hydraulic tank from deposits | When changing the oil or during washing | 1-2 hours | Technician (Level 2) |
| Inspection and calibration of manometers, thermometers | Annually | 30-60 min | KVPiA Technician (Level 3) |
Equivalent qualifications:
- Level 1: Basic knowledge of hydraulics, visual inspection, simple operations.
- Level 2: Experienced technician capable of replacing components, diagnostics.
- Level 3: Highly qualified specialist, engineer, able to carry out comprehensive diagnostics, adjustments and flushing.
9. Directory of Spare Parts
Availability of quality spare parts is essential for effective maintenance and quick troubleshooting. Below is a list of typical spare parts that may be required for hydraulic systems, with recommended specifications.
| Description Details | Typical Specification | Category UNITEC |
|---|---|---|
| The filtering element of the pressure line | Fineness of filtration 10 μm (absolute), Beta(c) ≥ 200, at Pnom 210 bar, connection G3/4" | Hydraulic filters |
| Filtering element of the drain line | Fineness of filtration 25 μm (absolute), Beta(c) ≥ 100, maximum flow 200 l/min, connection G1" | Hydraulic filters |
| Suction filter (mesh) | Fineness of filtration 125 μm, for immersion in a tank, connection G1 1/2" | Hydraulic filters |
| Filtering element for a washing unit | Filtration fineness 3 μm (absolute), Beta(c) ≥ 200, cell type PALL Ultipor III HC9600FCS8H | Filters for mobile systems |
| Sealing rings (O-Rings) | Material NBR (nitrile) or FKM (Vitron) for hydraulic oils, size sets according to EN ISO 3601 | Seals and oil seals |
| High pressure hydraulic hoses | DN19 (3/4"), PN 250 bar, according to EN 853 2SN, length on request | Hydraulic hoses and fittings |
| Quick disconnect connections | Type "Flat Face" (ISO 16028), size G1", material steel, PN 250 bar | Hydraulic hoses and fittings |
| Control manometer | Diameter 63 mm, range 0-250 bar, accuracy class 1.0, connection G1/4" | Measuring devices |
| Hydraulic pump (washer pump) | Geared, performance 50-150 l/min, PN 10-20 bar, connection G1" | Hydraulic pumps |
| Hydraulic oil | HLP 46, purity class ISO 17/15/12, viscosity 46 cSt at 40°C, according to EN ISO 11158 | Hydraulic oils and lubricants |
To purchase original and certified spare parts, refer to the UNITEC-D e-catalog: www.unitecd.com/e-catalog/.
10. Links
10.1. National and International Standards
- DSTU ISO 4406: Volumetric drive hydraulics. Working fluids. The method of coding the level of pollution by solid particles.
- DSTU EN ISO 12100: Machine safety. General design principles. Risk assessment and risk reduction.
- DSTU EN ISO 14118: Machine safety. Prevention of unexpected start.
- ISO 11158: Hydraulic fluids. Minimum requirements for hydraulic fluids. Categories HM, HV, HL, HG.
- ISO 3104: Petroleum products. Transparent and opaque liquids. Determination of kinematic viscosity and calculation of dynamic viscosity.
- ISO 3722: Volumetric drive hydraulics. Sampling method for determining the purity of solid particles.
- ISO 6789: Assembly tools for threaded connections. Manual torque wrenches.
- ISO 16028: Volumetric drive hydraulics. Quick release couplings. Application in the full range of pressures with a "flat" contact surface.
- EN 166: Personal eye protection. Technical requirements.
- EN ISO 374-1: The gloves are protective against dangerous chemicals and microorganisms. Part 1 Terminology and performance requirements for risks associated with chemicals.
- EN ISO 20345: Personal protective equipment. Protective shoes.
10.2. OEM Documentation
- Operation manuals: Always refer to the manufacturer's manuals for specific hydraulic equipment. They contain specific instructions for operation, maintenance, recommended fluids, tightening torques, maintenance and troubleshooting schedules tailored to the system design.
- Hydraulic diagrams: Detailed hydraulic diagrams of equipment are critical to understanding system operation and identifying components.
- Component Specifications: Data sheets and brochures for individual hydraulic pumps, valves, cylinders and filters.
