1. Scope and purpose
This maintenance manual provides step-by-step instructions for qualified technicians to perform critical maintenance work on industrial reciprocating compressors. Procedures described include inspection of valve plates, replacement of piston rings, and replacement of crankcase oil. These works are essential for ensuring reliable, efficient and safe operation of compressor equipment at industrial facilities in Ukraine. Regular implementation of these procedures minimizes the risks of unexpected failures, reduces operating costs and extends the service life of the compressor in accordance with the requirements of DSTU EN 1012-1:2018 "Compressors and vacuum pumps. Safety requirements" and ISO 8573-1:2010 "Compressed air. Part 1: Contamination and classes of purity". This manual is intended for scheduled preventive maintenance, as well as for the elimination of malfunctions associated with reduced performance, increased oil consumption, or extraneous noises.
2. Precautions
ATTENTION: Before starting any maintenance work on the compressor, be sure to complete the complete lockout/marking procedure (LOTO) in accordance with DSTU EN 1037:2004 "Machine Safety. Prevention of unexpected start-up". Failure to do so could result in serious injury or death.
WARNING: Compressed air is dangerous. Before disassembling the compressor, completely depressurize all systems. Make sure all power lines (electrical, pneumatic, hydraulic) are de-energized and blocked. Use appropriate personal protective equipment (PPE): safety glasses, work gloves, protective shoes and hearing protection (according to DSTU EN 352-1:2017). When working with lubricants, use gloves resistant to chemicals.
3. Necessary tools and materials
| The name of the tool/material | Specification | Quantity |
|---|---|---|
| A set of socket wrenches | 8-32 mm | 1 set |
| A set of end heads | 8-32 mm, 1/2" drive | 1 set |
| Torque wrench | Range 20-200 Nm, accuracy ±4% (according to ISO 6789) | 1 pc. |
| Measuring probe (set) | 0.05-1.0 mm with a step of 0.05 mm | 1 set |
| Key for removing the oil filter | Corresponds to the diameter of the filter | 1 pc. |
| Container for collecting used grease | The capacity is not less than 20 liters | 1 pc. |
| Clean lint-free napkins | Industrial | As needed |
| Cleaner for parts | No residue, quick drying | 1 aerosol |
| New compressor oil | ISO VG 100 or 150, according to the manufacturer's specification | From 10 to 20 liters (depending on the volume of the crankcase) |
| New piston rings | Corresponding compressor models and cylinder sizes | 1 set per piston |
| New gaskets | For cylinder head, valve plates, crankcase | 1 set |
| Device for compressing piston rings | Corresponds to the diameter of the piston | 1 pc. |
| Screwdrivers | Flat, cross-shaped | 1 set |
| Copper or aluminum brush | For cleaning surfaces | 1 pc. |
4. Inspection before service (checklist)
| Item | Verification | Acceptance/rejection criteria | Notes |
|---|---|---|---|
| General visual inspection | The presence of visible damage, cracks, deformations of the case. | No damage. | |
| Oil/air leaks | Checking connections, gaskets, seals for leaks. | Complete absence of leaks. | Lubricant leaks may indicate damaged seals or loosening of fasteners. |
| Oil level in the crankcase | Checking the oil level indicator. | The oil level should be between the "MIN" and "MAX" marks. | Insufficient level can cause wear, excessive - foaming and temperature rise. |
| Compressor operating temperature | Monitoring of oil and cylinder temperatures during operation. | The temperature of the lubricant should not exceed 80°C. The temperature of the cylinder heads is within the manufacturer's norm. | A high temperature indicates overload, cooling problems, or excessive friction. |
| Injection pressure | Checking the working pressure with a manometer. | Compliance with the nominal working pressure (for example, 7-10 bar). | Low pressure may indicate faulty valves or piston rings. |
| Extraneous noises and vibrations | Listening to the operation of the compressor, visual inspection for vibrations. | Smooth, uniform operation without unusual noises (knocking, grinding) and excessive vibrations. | A metallic knock can indicate worn bearings, pistons, or valves. |
| Condition of the air filter | Visual inspection of the filter element. | Absence of significant pollution, damage. | A dirty filter reduces compressor performance and accelerates wear. |
5. Step-by-step procedure
5.1. Training and safety
- Perform a lockout/tagout (LOTO) procedure for the compressor. MUST make sure the power supply is disconnected and the main switch is locked in the OFF position. Check the absence of voltage with an appropriate device (for example, a multimeter according to DSTU IEC 61010-1:2019).
- Completely depressurize the entire compressed air system. Open all drain valves and bleed air from the receiver. Wait until the pressure gauges show 0 bar.
- Place a clean container under the work area to collect used grease.
5.2. Oil change in the crankcase
- Compressor warm-up (if needed): If the compressor is cold, run it for 5-10 minutes to warm the oil up to operating temperature (about 40-50°C). Avoid excessive heating to avoid burns.
- Draining used oil: Unscrew the drain plug in the lower part of the crankcase. Allow the lubricant to completely drain into the prepared container. This may take 15-30 minutes. Take your time, make sure all the grease is drained.
- Replacing the oil filter: Unscrew the old oil filter using a special wrench. Clean the seat of the filter from remaining grease and dirt. Apply a thin layer of fresh lubricant to the rubber gasket of the new filter. Tighten the new filter by hand until it is tight, then tighten another 3/4 turn. Do not drag the filter, it may damage the gasket.
- Filling with new oil: Screw in the crankcase drain plug, making sure a new gasket is installed (if necessary) and tighten it with a torque wrench to the torque specified in the manufacturer's manual (typically 25-35 Nm). Pour new compressor oil (e.g. ISO VG 100 or 150) through the filler hole up to the "MAX" mark on the dipstick. Use only the oil recommended by the manufacturer to avoid damage to the compressor.
- Checking the oil level: After refueling, run the compressor for a short time (about 30 seconds), then turn it off and wait 5 minutes for the oil to clear. Check the oil level and, if necessary, bring it to the "MAX" mark.
5.3. Overview of valve plates
- Dismantling the cylinder heads: Carefully unscrew the cylinder head mounting bolts. For uniform removal, loosen the bolts diagonally in several stages. Remove the cylinder heads and old gaskets. Keep all fasteners in order to avoid loss or confusion during assembly.
- Accessing the valve plates: After removing the cylinder heads, you will gain access to the intake and exhaust valve plates. Depending on the design, it may be necessary to remove additional elements.
- Visual Inspection: Carefully inspect each valve plate. Look out for:
- Cracks or chips: On valves, seats or the plate itself. Even micro-cracks can lead to significant performance losses.
- Wear: Signs of wear on valves or seats. The presence of burrs, irregularities.
- Soot: Excessive formation of carbon deposits. Fresh soot may indicate that lubricant has entered the working chamber, old soot may indicate overheating.
- Spring damage: If the valves have springs, check them for integrity and no deformation.
- Deformation: Estimate the flatness of the valve plate and cylinder heads using a calibrated ruler and feeler gauge. The permissible deviation from flatness is no more than 0.05 mm per 100 mm of length. Deformation requires replacement or machining.
- Cleaning: Use parts cleaner and a copper or aluminum brush to remove soot and deposits. Clean the channels in the cylinder heads. Use only soft metal brushes to avoid damaging surfaces.
- Replacement of Damaged Items: Replace any damaged valve plates, valves, seats or springs found. Use only original spare parts or high-quality analogues.
- Installation: Install new valve plate and cylinder head gaskets. Carefully install the cylinder heads, focusing on the guide pins. Tighten the fastening bolts with a torque wrench, following the recommended torque (for example, M8: 25-30 Nm; M10: 45-55 Nm) and the tightening pattern (diagonally, in several stages). Don't forget new gaskets, reusing them will cause leaks.
5.4. Replacement of piston rings
This procedure requires considerable care and precision.
- Access to the pistons: If the cylinder heads are already removed (as in the previous step), proceed to the next step. Otherwise, disassemble the cylinder heads and valve plates as described in paragraph 5.3.1.
- Removing the pistons: Unscrew the bolts of the connecting rod covers that fasten the connecting rod to the crankshaft. Carefully push the piston up out of the cylinder. Be careful not to damage the cylinder mirror when pulling out the piston.
- Cleaning pistons and grooves: Thoroughly clean the piston from soot and deposits. Pay special attention to the grooves for the piston rings. Use a special tool for cleaning the grooves or a piece of an old piston ring. Do not use metal brushes or abrasive materials that can damage the piston surface.
- Removing the old piston rings: Using special piston ring pliers or carefully remove the old rings by hand. Do not overstretch the rings to avoid damaging the piston.
- Piston Inspection: Inspect the piston for cracks, burrs, or wear. Check piston pin play.
- Installing new piston rings:
- Checking the lock clearance: Before installing each ring, insert it into the cylinder (without the piston) about 20mm from the top edge and measure the lock clearance with a feeler gauge. The permissible gap must meet the manufacturer's specification (usually 0.25-0.5 mm). If the gap is smaller, carefully file the ends of the ring. If the gap is larger, the ring is unusable.
- Installation sequence: Install the rings, starting with the lower (oil-removable) one. Use piston ring pliers to gently expand the ring and slide it onto the piston. Follow the correct orientation of the rings if they are marked "TOP" or taper.
- Lock placement: After all rings are installed, position their locks at 120° to each other (or according to manufacturer's recommendations) to avoid overlapping locks.
- Installing the piston into the cylinder: Lubricate the piston, piston rings and cylinder mirror with clean compressor oil. Use a piston ring crimper to carefully insert the piston into the cylinder. Be very careful not to damage the cylinder mirror or piston rings during installation.
- Connecting the connecting rod: Connect the connecting rod to the crankshaft by installing new bushings (if necessary) and tightening the connecting rod cap bolts with a torque wrench to the torque specified by the manufacturer (eg 40-50 Nm for M10). Be sure to use a new fastening (bolts) of connecting rods, if this is provided by the manufacturer.
- Assembly: Install the valve plates and cylinder heads with new gaskets, tightening the bolts according to the manufacturer's recommendations (see paragraph 5.3.6).
6. Inspection after service (checklist)
| Test/Check | Expected result | Actual result | Pass/Fail |
|---|---|---|---|
| Visual inspection after assembly | No open connections, no tools left. | ||
| Checking the oil level | The oil level is between the "MIN" and "MAX" marks. | ||
| System tightness | No oil or air leaks during operation. | ||
| The first start of the compressor | Smooth start-up, without unusual noises and vibrations. | ||
| Monitoring of injection pressure | Achieving and maintaining nominal working pressure. | ||
| Monitoring of working temperature | The temperature of the oil and cylinders is within normal limits. | ||
| Checking the presence of emergency signals | Absence of activation of emergency signals. | ||
| Control for the first 1-2 hours of work | Stable operation, no anomalies. |
7. Troubleshooting guide
| Symptom | Probable cause | Corrective action |
|---|---|---|
| Low injection pressure / insufficient performance | Wear or damage to valve plates (intake/discharge). Wear of piston rings. Air leaks through cylinder head gaskets. |
Inspect and replace valve plates. Replace piston rings. Replace gaskets, check bolt torque. |
| Increased oil consumption / presence of oil in compressed air | Severe wear of oil-removable piston rings. Cylinder wear. Clogged crankcase ventilation system. |
Replace the piston rings. Bore the cylinder or replace the sleeve/cylinder. Clean or replace the crankcase ventilation system. |
| Extraneous knocking in the crankcase / cylinders | Wear of connecting rod or main bearings. Wear of piston pin and/or bushing. Loose connection of connecting rods. Piston damage. |
Inspect and replace bearings. Inspect and replace piston pin and sleeve. Check and tighten connecting rod bolts with a torque wrench. Inspect and replace piston. |
| Compressor overheating | Insufficient oil level. Incorrect type of oil used. Contaminated or damaged valve plates. Clogged air filter. Insufficient cooling (e.g. dirty radiator). |
Bring the oil level to normal. Replace the oil recommended by the manufacturer. Inspect and replace the valve plates. Replace the air filter. Clean the cooling system. |
| Excessive vibration | Imbalance of moving parts. Loose fastening of the compressor to the foundation. Wearing of bearings. |
Carry out balancing. Check and tighten fastening bolts. Inspect and replace bearings. |
8. Recommended maintenance schedule
| Task | Frequency | Estimated duration | Qualification level |
|---|---|---|---|
| Checking the oil level | Every day | 5 min | Operator/Technician |
| Checking for leaks and extraneous noises | Every day | 10 min | Operator/Technician |
| Oil change in the crankcase | Every 500-1000 engine hours or 6 months (depending on operating conditions and type of lubricant) | 1.5-2 hours | Technician |
| Replacing the oil filter | At each oil change | 0.5 hours | Technician |
| Air filter inspection/replacement | Every 250-500 engine hours or 3 months (more often in dusty conditions) | 0.5-1 hour | Technician |
| Overview of valve plates | Every 2000-4000 engine hours or annually | 4-6 hours | Experienced technician |
| Replacement of piston rings | Every 4000-8000 engine hours or when performance decreases/increased oil consumption | 8-16 hours | Experienced technician/engineer |
| General overhaul | Every 10,000-20,000 engine hours | Depends on the scope of work | Specialized team/Service center |
9. Directory of spare parts
| Description of the part | Typical specification | Category UNITEC |
|---|---|---|
| Piston rings (set) | High strength cast iron, alloy steel; size according to the diameter of the cylinder | Compressor spare parts |
| Suction/discharge valve plate | Alloy steel, special composite materials; according to the compressor model | Compressor spare parts |
| Set of gaskets (for heads, valves, crankcase) | Asbestos-free paronite, metal-filled; resistant to grease and high temperatures | Sealing |
| Oil filter | Type: cartridge/screw; degree of filtration: 10-25 microns; corresponding to the compressor model | Filters |
| Compressor oil | ISO VG 100 or 150 (depending on the model); mineral/synthetic | Lubricating materials |
| Air filter (suction) | Paper or synthetic element; filtration class G3/G4 (according to DSTU EN 779:2006); corresponding to the compressor model | Filters |
| Connecting rod bushings | Multi-layer, anti-friction alloy; corresponding compressor models | Compressor spare parts |
| Connecting rod bolts | High-strength steel, strength class 10.9 or 12.9; size and length according to the model | Fastening elements |
Look for these and other required components in the UNITEC-D catalog: https://www.unitecd.com/e-catalog/
10. Links
- DSTU EN 1012-1:2018 "Compressors and vacuum pumps. Security requirements".
- DSTU EN 1037:2004 "Safety of machines. Prevention of unexpected start-up".
- DSTU EN 352-1:2017 "Means of individual protection of hearing organs. Protective headphones".
- DSTU IEC 61010-1:2019 "Safety requirements for electrical control and measurement equipment and laboratory equipment. Part 1: General requirements".
- ISO 8573-1:2010 "Compressed air. Part 1: Contamination and classes of purity".
- ISO 6789:2017 "Loading and measuring tools for bolted connections. Manual load-measuring spanners. Requirements and test methods for conformity".
- DSTU EN 779:2006 "Anti-dust air filters for general ventilation. Determination of working characteristics".
- Compressor manufacturer (OEM) documentation.
