Maintenance Guides 1 min read

Maintenance of the air preparation unit (FRL): replacement of filter elements, diaphragms of the regulator and filling of the lubricator

Technical analysis: Air preparation unit (FRL) maintenance checklist: filter elements, regulator diaphragms, lubricator

Технічне обслуговування блоку підготовки повітря (FRL): заміна фільтруючих елементів, діафрагм регулятора та заправка мастильника - UNITEC-D Industrial MRO

Scope & Purpose

This manual is intended for the maintenance of compressed air preparation units (FRL - Filter-Regulator-Lubricator) in industrial pneumatic systems. Covers the following operations:

  • Replacement of filter elements (coalescent and dust filters)
  • Inspection and replacement of pressure regulator diaphragms
  • Refueling and adjustment of the lubricator
  • Cleaning and checking the tightness of nodes

Maintenance is carried out in accordance with DSTU EN ISO 8573-1:2016 (purity of compressed air) and DSTU EN 983:2015 (safety requirements for pneumatic systems). The recommended frequency is every 2000 hours of operation or once every 6 months (depending on operating conditions).

Safety Precautions

ATTENTION! BEFORE STARTING WORK:

  • Turn off the power to the compressor and de-energize the pneumatic system. Perform the Lockout/Tagout procedure according to DSTU EN 1037:2015.
  • Relieve the residual pressure in the system. Open the drain valve until the air has completely stopped escaping (minimum 30 seconds). The pressure in the system should be 0 bar.
  • Use personal protective equipment (PPE): safety glasses (EN 166), gloves (EN 388), safety shoes (EN ISO 20345).
  • Do not allow grease to fall on the floor - use a tray to collect the used liquid.
  • Work in a well-ventilated area. Lubricant vapors can cause respiratory tract irritation.

Tools & Materials Required

Tool/Material Specification Quantity
Dynamometric key Range 5–50 Nm, accuracy class ±3% 1
The screwdriver is insulated PH2 slot, insulation up to 1000 V (EN 60900) 1
Horn key Size 17mm, 19mm, 22mm 1 set
Control manometer Range 0–10 bar, accuracy class ±0.5% 1
Vernier caliper Digital, range 0-150mm, accuracy ±0.02mm 1
Pneumatic leak detector Sensitivity 1×10-6 mbar·l/s 1
Lubricant for pneumatics ISO VG 32 or ISO VG 46 (according to DSTU ISO 3448:2015) such as Mobil DTE 24 500 ml
Filter element Coalescent filter, class 1 μm (according to ISO 8573-1) 1
Diaphragm regulator Nitrile rubber (NBR), diameter 40–60 mm (depending on the model) 1
Sealing gaskets Silicone or fluororubber (FKM), thickness 1.5 mm 2–4 pcs.
Lint-free rags For cleaning surfaces 5 pcs.
Spray for cleaning No residue like CRC Contact Cleaner 1 balloon

Pre-Maintenance Inspection Checklist

Item Verification Acceptance/rejection criteria Notes
1. Pressure in the system Check the pressure gauge at the FRL outlet The pressure should be 0 bar. If >0.5 bar – the system is not de-energized. Use a control manometer for verification.
2. State of the filter element Visual inspection and pressure drop check Pressure drop > 0.5 bar or visible contamination - replacement is mandatory. For coalescent filters - the presence of an oil film on the surface.
3. Airtightness of connections Checking with a leak detector or soap solution The presence of bubbles is a leak. 0 bubbles allowed in 10 seconds. Pay special attention to threaded connections and seals.
4. Operation of the pressure regulator Turn the adjusting screw by ±1 turn The pressure should change smoothly, without jumps. If jumps > 0.2 bar – the diaphragm is damaged. Check for cracks on the regulator housing.
5. Lubrication level in the lubricator The inspection is visual through the sight glass Level below 50% - refueling required. If the lubricant is dark/dirty, replace it. Use only the recommended type of lubricant.
6. Condition of the drain valve Manual opening/closing check The valve should open freely, without jamming. The presence of corrosion - replacement. Clean the valve from dirt before checking.
7. Electrical connections (if any) Inspection of insulation and fastening Insulation resistance > 1 MΩ (measure with a megohmmeter at 500 V). The presence of oxidation - clean. Only for FRL with electronic control.

Step-by-Step Procedure

1. Dismantling the filter element

  1. Remove the filter cover.
    • Unscrew the cover fastening bolts (tightening torque 12–15 Nm). Use a torque wrench.
    • Remove the cover carefully - there may be residual condensate inside.
    • Avoid dropping the lid - it may damage the seal.
  2. Pull out the filter element.
    • Pull the element vertically upwards. If stuck, gently shake from side to side.
    • Inspect the element for mechanical damage (cracks, deformations).
    • Do not use metal tools for extraction - it can damage the filter housing.
  3. Clean the filter housing.
    • Remove condensation and dirt from the housing with a lint-free cloth.
    • Wipe the sealing surface with a cleaning spray. Make sure there are no scratches or corrosion.
    • Check the condition of the sealing ring - if there are cracks or deformations, replace it.

2. Replacement of the diaphragm of the pressure regulator

  1. Dismantle the pressure regulator.
    • Unscrew the regulator from the FRL housing (tightening torque 20–25 Nm).
    • Remove the adjusting screw and spring. Place them in a clean tray.
    • Do not lose small parts (washers, seals).
  2. Pull out the diaphragm.
    • Remove the upper cover of the regulator (bolts 8–10 Nm).
    • Gently pull out the diaphragm. Check it for cracks, breaks or deformations.
    • Measure the thickness of the diaphragm with a caliper - it should be 1.0-1.2 mm. If less, replacement is mandatory.
  3. Install the new diaphragm.
    • Grease the new diaphragm with a thin layer of grease (ISO VG 32).
    • Place the diaphragm in place, making sure it is flush in the slot.
    • Tighten the top cover (torque 8–10 Nm).
    • Do not overtighten the bolts - it can damage the diaphragm.
  4. Assemble the regulator.
    • Install the spring and adjusting screw.
    • Attach the regulator to the FRL housing (torque 20–25 Nm).
    • Adjust pressure to 6 bar (or according to system requirements).

3. Refilling the lubricant

  1. Drain the used lubricant.
    • Place a tray under the oiler drain valve.
    • Open the valve and drain all the oil. Close the valve after draining.
    • Do not allow grease to fall on the floor - use a pallet.
  2. Clean the lubricator.
    • Fill the lubricator with cleaning spray and shake.
    • Drain the liquid through the drain valve.
    • Repeat the procedure until complete cleaning.
  3. Fill in fresh lubricant.
    • Fill the lubricant up to the level of 75% (by sight glass).
    • Use only the recommended lubricant (ISO VG 32/46).
    • Close the lubricator cover (torque 5–7 Nm).
  4. Adjust the oil flow.
    • Turn the oiler adjustment screw 1/4 turn clockwise (minimum flow).
    • Connect the system and check for oil at the outlet (visually or using a paper filter).
    • Gradually increase the flow until the optimal level is reached (usually 1 drop per 10 m³ of air).

4. Assembly and verification of FRL

  1. Install a new filter element.
    • Insert the element into the filter housing, ensuring the correct orientation (the arrow on the element should point down).
    • Install the filter cover and tighten the bolts (torque 12–15 Nm).
  2. Check for tightness.
    • Connect a control pressure gauge to the FRL outlet.
    • Apply compressed air at a pressure of 7 bar.
    • Apply a soapy solution to all connections. The presence of bubbles is a leak.
    • If there is a leak, tighten the connection or replace the seal.
  3. Adjust the pressure.
    • Set the outlet pressure 6±0.2 bar using the adjusting screw.
    • Check the stability of the pressure - fluctuations should not exceed ±0.1 bar.
  4. Check the operation of the lubricator.
    • Start the system and make sure that the lubricant reaches the outlet.
    • Adjust oil flow as needed.

Post-Maintenance Verification Checklist

Check Expected result Actual result Passport/No passport
Airtightness of all connections No leaks (0 bubbles in 10 s)
FRL outlet pressure 6±0.2 bar (or according to requirements)
Pressure stability Fluctuations ≤ ±0.1 bar
Operation of the lubricator Lubricant flows to the outlet (1 drop/10 m³)
Operation of the drain valve The valve opens/closes freely, without leaks
Pressure drop across the filter ≤ 0.3 bar (for a new element)
Absence of extraneous noises No whistling, knocking or vibration

Troubleshooting Guide

Symptom Probable cause Corrective action
Outlet pressure below normal
  • Damaged regulator diaphragm
  • Dirty filter element
  • Leakage in joints
  • Replace the diaphragm
  • Replace the filter element
  • Check for leaks and tighten the connections
Outlet pressure is higher than normal
  • Jamming of the adjusting screw
  • Damage to the regulator spring
  • Disassemble the regulator, clean and lubricate the screw
  • Replace the spring
Air leaks from the regulator
  • Damaged diaphragm seal
  • A crack in the regulator housing
  • Replace the seal
  • Replace the housing or the entire regulator
Grease does not reach the outlet
  • Contaminated lubricant dispenser
  • Low oil level
  • Clogging of the oil line
  • Clean the dispenser
  • Add oil
  • Clean the oil line
Increased pressure drop across the filter
  • Contaminated filter element
  • Incorrectly installed item
  • Replace the element
  • Check that the installation is correct
Extraneous noises (whistling, knocking)
  • Damage to the bearings of the lubricator
  • Vibration due to loose mounting
  • Replace the lubricant
  • Check and tighten fasteners

Recommended Maintenance Schedule

Task Periodicity Estimated completion time Qualification level
Pressure and tightness test Every month 15 minutes Technician
Cleaning the drain valve Every 3 months 20 minutes Technician
Replacement of the filter element Every 2000 hours or 6 months 45 minutes Qualified technician
Replacement of the regulator diaphragm Every 4000 hours or 12 months 60 minutes Qualified technician
Refilling/replacing the lubricant in the lubricator Every 2000 hours or 6 months 30 minutes Technician
Full FRL Maintenance Every 8000 hours or 24 months 2 hours Qualified technician

Spare Parts Reference

Part description Typical specification UNITEC-D category
Coalescent filter element Class 1 micron, polypropylene, diameter 40–60 mm FRL-FILTER-ELEMENT
Dust filter element Class 5 micron, polyester, diameter 40–60 mm FRL-DUST-FILTER
Pressure regulator diaphragm NBR, diameter 40–60 mm, thickness 1.0–1.2 mm FRL-REGULATOR-DIAPHRAGM
Sealing ring for the filter Silicone or FKM, diameter 50–70 mm FRL-SEAL-RING
Lubricant for pneumatics ISO VG 32 or ISO VG 46, 1 l FRL-LUBRICANT
Drain valve Automatic or manual, thread G1/4

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