Filter Inspection and Replacement

A paint-booth filter is a working component of the ventilation system. As it collects atmospheric dust or overspray, its resistance, loading distribution and mechanical condition change. These changes can reduce airflow, disturb booth balance, increase fan effort, promote bypass or allow paint to reach downstream surfaces. A clean-looking bank may still contain gaps or deep loading; a visibly coloured bank may still be stable. Inspection therefore needs a repeatable route and comparable operating information. [S171; S178; S195]

This chapter is an educational and application-selection guide. The installed booth method, coating Safety Data Sheet, applicable Malaysian requirements and current product information remain controlling. Where an exact product value is required, Refer to the product label, Technical Data Sheet, or MKTECH representative.

Chapter objectives

After this chapter, the reader should be able to:

• conduct a structured visual inspection of intake, diffusion and exhaust-filter banks;
• establish a clean-bank pressure and airflow baseline after correct installation;
• distinguish normal loading from uneven loading, bypass, collapse and breakthrough;
• interpret pressure-drop and airflow trends together rather than as isolated readings;
• set replacement timing from the earliest relevant condition endpoint;
• confirm airflow direction, frame sealing, support and gauge condition during change-out;
• release a replaced bank only after physical and operational checks pass;
• maintain concise records that support maintenance, purchasing, safety and Malaysian waste control; and
• diagnose repeated short life without substituting an unsuitable filter or unsafe fan adjustment.

Inspection begins before touching the filter. Observe the booth while it is operating in its normal approved arrangement, then inspect the filter bank under the booth's isolation and access procedure. The useful inspection path follows the air:

1. room or make-up-air intake;
2. prefilter and supply-air stages;
3. ceiling or diffusion media;
4. booth work zone and openings;
5. exhaust paint-arrestor face;
6. supporting grid, frame and perimeter;
7. downstream plenum, duct and fan approach; and
8. pressure taps, gauge, alarms and control indication.

This route prevents a loaded exhaust filter from being blamed for a blocked intake, shut damper, dirty plenum, damaged fan or gauge fault. DOSH Malaysia treats local exhaust ventilation as a complete system of hood or enclosure, duct, air cleaner and fan, with regular inspection and maintenance of all components. [S171]

Visual inspection is strongest when the same zones, lighting and observation order are used each time. Inspect with the bank operating where observation is safe and permitted; complete hands-on checks only after the required shutdown, run-on, clearance and isolation sequence.

Use photographs from fixed positions where practical. A close-up proves media condition; a full-bank photograph shows distribution. Record the booth state, filter stage, airflow direction and date so photographs remain meaningful.

The shape of the deposit often reveals more than its colour. Compare the current pattern with earlier photographs and the physical layout of parts, guns, openings and plenums.

Uneven loading is a symptom, not a diagnosis. Replacing only the darkest section can move airflow toward the new low-resistance area and make distribution less stable. Zone replacement is appropriate only where the booth and filter arrangement are designed and controlled for it.

Differential pressure is the resistance between two defined points. Across a filter bank, it normally increases as deposited material restricts the available flow paths. The reading is valuable only when the pressure taps, gauge, fan/control state, doors, dampers and airflow condition are comparable.

Before relying on a reading:

• confirm both pressure tubes are connected to the intended upstream and downstream points;
• inspect tubes for splits, kinks, condensation, paint blockage and reversed connections;
• check the instrument zero under its specified condition;
• confirm the gauge range and units are appropriate and legible;
• identify whether the reading covers one stage, several stages or the whole booth; and
• record fan speed or control state, door position and production condition.

Never convert a supplier's final-resistance value into a universal booth limit. The safe replacement point may be earlier because airflow, containment, motor load, physical stability, fire control or downstream cleanliness reaches its limit first. Refer to the product label, Technical Data Sheet, or MKTECH representative.

Pressure drop and airflow are related through the complete fan system, but one is not a substitute for the other. With a fixed-speed fan, increasing system resistance commonly reduces flow. With a controlled-flow system, the drive may increase fan effort to hold flow until it reaches a control or motor limit. A stable pressure reading can therefore accompany different airflow conditions if the control state changes. [S171; S194; S195]

Use one or more verified operational indicators appropriate to the booth:

• face or cross-sectional airflow measurement under the approved method;
• fixed-position velocity checks used for trending;
• airflow indicator, alarm or interlock status;
• smoke or visual containment test performed by a competent person with suitable test material;
• booth pressure relationship to the surrounding area;
• fan speed, drive output or motor condition; and
• overspray behaviour at openings and workpiece position.

DOSH guidance uses baseline testing for comparison and calls for investigation where reduced flow or malfunction is indicated. Keep the site's statutory inspection and examination programme separate from routine operator checks, while making the two records support each other. [S171]

Bypass

Bypass is air passing around rather than through the intended media. It follows gaps at the perimeter, open joints, damaged gaskets, missing clips, poor roll overlap, unsealed frame connections or holes. Because the bypass path has lower resistance, it can remain deceptively clean while a downstream streak accumulates.

Typical indicators are:

• clean line or corner beside a loaded face;
• media lifting or fluttering at an edge;
• pressure lower than the established condition would suggest;
• paint trail on the clean side aligned with a joint; and
• local downstream deposit despite apparently suitable media.

Correct bypass mechanically. A finer filter cannot compensate for an open seal. Camfil's installation guidance for filter frames uses gasket compression and sealing between frame joints to prevent air bypass; the same transferable principle applies to a paint-booth bank while the booth and selected filter instructions govern the actual hardware. [S196]

Collapse

Collapse is loss of the media's intended shape or support under airflow, deposit weight, moisture or incorrect installation. It includes sagging, bowing, pleats pulling together, a pad being drawn through the grid, a pocket folding over, or a roll detaching from its anchorage.

Common contributors include reverse direction, insufficient support, excessive span, over-expansion or under-expansion, saturated deposit, media incompatible with the duty, abnormal pressure, damaged frame or missing retainers. Collapse can create both high local resistance and open bypass paths.

Stop spraying when the bank cannot retain its intended geometry. Replace the damaged section or bank, restore support and investigate the cause before restart.

Breakthrough

Breakthrough is paint or particulate appearing downstream of the installed filter system. It may be genuine penetration through intact media, but it can also result from bypass, tearing, poor joints, reverse installation, overloaded media, displaced backing or an unsuitable first/final-stage combination.

Confirm the route before selecting a finer grade:

1. identify whether the deposit is wet paint, dry residue, rust, old contamination or other dust;
2. trace its position back to the filter face, joints and frame;
3. inspect direction, backing and mechanical condition;
4. confirm the coating, atomisation and spray rate have not changed;
5. check the downstream stage and pressure/airflow trend; and
6. clean a defined downstream observation area so recurrence can be verified.

Replacement timing should be predictable but not arbitrary. A calendar schedule supports planning and inspection; it does not override an earlier physical or operational limit.

Replace at the earliest applicable endpoint:

1. Declared filter endpoint: the product's stated final resistance, loading or service condition.
2. Booth airflow endpoint: required airflow, containment or control range can no longer be maintained.
3. Physical endpoint: tear, hole, sag, collapse, loose backing, run-off, detachment or damaged seal.
4. Downstream endpoint: unacceptable breakthrough, deposit or protection loss.
5. Fire/chemical endpoint: residue compatibility, heat, smoke, odour, curing or housekeeping condition requires removal.
6. Process-quality endpoint: verified filtration condition is causing dust, dry spray, turbulence or finish defects.
7. Maintenance endpoint: the planned stoppage is the safe opportunity to replace a bank that would not reliably complete the next production period.

For an exact replacement value or interval, Refer to the product label, Technical Data Sheet, or MKTECH representative.

Loaded filters can contain wet coating, solvent, reactive hardener and combustible residue. Plan the change around the coating SDS, chemical assessment, booth procedure, fire controls and waste route.

Before starting:

• stop spraying and complete the specified ventilation run-on or clearance period;
• isolate equipment and energy sources under the site procedure;
• confirm that the filter area is safe to enter and that required fire protection remains available;
• identify the coating residues and select the specified PPE and handling controls;
• prepare compatible, labelled waste containers close enough to prevent uncontrolled carrying;
• protect the clean side, booth floor and nearby components from released deposits;
• prepare the correct replacement identity, quantity, direction and support hardware; and
• prohibit hot work, ignition sources and compressed-air blow-off of paint deposits.

Do not shake, tear or drag loaded media across clean surfaces. Do not cut into a wet or heavily loaded pocket unless the approved method specifically requires it. Do not stack warm, wet or actively curing filters in an enclosed combustible pile.

1. Record the last comparable pressure, airflow/containment condition and observed loading pattern.
2. Photograph the bank before removal if failure pattern or service life is being investigated.
3. Remove media in manageable sections, supporting its weight and keeping the loaded face controlled.
4. Place each section directly into the prepared container; segregate incompatible residues.
5. Inspect the exposed frame, clips, grids, channels, gaskets and downstream side.
6. Remove accessible loose residue by the booth's approved non-sparking, low-dispersion method.
7. Check pressure taps and tubing without pushing contamination into the system.
8. Record damage that needs repair before new media is installed.

Replacing media over a dirty, warped or unsealed frame preserves the failure. Frame cleaning is complete only when the seating surface can make a continuous seal and the downstream side is suitable for detecting new breakthrough.

Filter media can be directional. Direction may be identified by an airflow arrow, upstream/downstream label, colour, backing, graduated density, pocket orientation, pleat geometry or product instructions. Appearance is not a reliable substitute for declared installation information.

Use this installation sequence:

1. verify filter identity against the work order and installed location;
2. identify airflow direction and the declared spray or dust side;
3. inspect the replacement for moisture, crushing, tears, delamination or transport damage;
4. clean and repair the seating frame before placing media;
5. fit the media without compressing its designed depth or distorting pleats and pockets;
6. close every joint, overlap and perimeter in the specified sequence;
7. engage all clips, retainers, grids and anchors so deposit weight and airflow cannot displace the media;
8. inspect both upstream and downstream sides where accessible; and
9. confirm that no frame opening or unused area is exposed.

Roll and accordion media must be expanded or overlapped as specified. Under-expansion can reduce internal storage and leave open joints; over-expansion can flatten geometry and change resistance. Pocket and panel filters must be seated against the correct gasket face and supported in the intended airflow direction. Refer to the product label, Technical Data Sheet, or MKTECH representative.

A sealed bank directs air through the media. Use a systematic perimeter-to-centre check:

• Perimeter: continuous contact with no visible daylight, folded edge or broken gasket.
• Corners: clips engaged and media not pulled away by tension.
• Joints: specified overlap, compression or sealing strip is continuous.
• Centre: no missing panel, crushed section or unsupported span.
• Retainers: installed without cutting, puncturing or excessively compressing media.
• Frame: square enough to seat the filter; no corrosion, dried paint ridge or damage holding an edge open.
• Downstream: no loose piece can be drawn into the fan or duct.

Where several frames form a bank, seal between the frames and between the bank and surrounding plenum as required. A perfect media-to-frame seal cannot correct leakage around the frame assembly itself. [S196]

The first controlled operating condition after replacement becomes the reference for later trending. Record it only after the bank has passed physical checks.

Release sequence:

1. account for tools, offcuts and removed media;
2. close access panels and restore guards, fire protection, pressure tubing and interlocks;
3. remove isolation under the authorised procedure and start ventilation without spraying;
4. observe the bank for flutter, movement, abnormal noise or pulling at joints;
5. check the gauge zero/response and record the clean differential pressure;
6. verify airflow, containment and booth pressure by the established method;
7. inspect the downstream observation area and booth openings;
8. conduct the authorised production check using normal coating and operating conditions; and
9. record filter identity, installation date, baseline and release decision.

Stop and correct the installation if the clean reading, airflow or containment differs materially from the established condition, or if any gap, movement, unusual odour, smoke, heat or downstream deposit is observed.

A concise record should support the next operator, maintenance planner, environmental coordinator and purchaser. It should explain what changed and why without relying on memory.

Use trends to forecast stock, not to create an unqualified guarantee. Service life can change with coating solids, spray rate, transfer efficiency, part geometry, operator technique, ambient dust, humidity, airflow and media construction. [S178; S195]

Used-filter classification follows the captured coating residue and the generating process. The waste generator identifies the applicable category using process and chemical information; the clean carrier material alone does not determine the route.

DOE Malaysia requires scheduled waste, where applicable, to follow prescribed storage, labelling, inventory, transport and authorised-receiving controls. [S188; S189]

Use the following record chain:

1. link the removed filter to the coating, hardener, thinner and process period;
2. determine the applicable waste classification from the actual residue and generating process;
3. segregate incompatible waste streams;
4. record the date, quantity, container identity and designated storage location;
5. maintain the required current inventory and labels;
6. use authorised transport and receiving arrangements where required; and
7. retain the applicable inventory and movement records for the prescribed period.

Do not assign one universal waste code to all paint-booth filters. DOE Malaysia states that the waste producer is responsible for classification because it knows the raw materials and generating process. [S189]

Repeated failure after correct installation is a system signal. Re-run the Chapter 034 selection method using the current coating, overspray volume, booth airflow, effective area, pressure allowance, capture duty and disposal route.

• Keep ventilation, interlocks, grounding and fire protection in their designed operating state.
• Stop spraying for tears, open gaps, collapse, run-off, breakthrough, loss of containment, heat, smoke or smouldering odour.
• Do not use gauge pressure as the only proof of airflow or capture.
• Never increase fan limits to conceal a loaded or unsuitable filter.
• Do not mix filter residues from coatings that can react or self-heat together.
• Prevent ignition sources and uncontrolled compressed-air cleaning in paint and filter areas.
• Wear the PPE and use the handling method specified by the coating assessment and booth procedure.
• Place removed filters directly into the correct compatible container; do not leave them beside the booth.
• Treat used filters according to the captured residue and applicable Malaysian waste requirements.
• Verify direction, sealing, support, pressure indication, airflow and downstream condition before production release.

Paint-Booth Troubleshooting appears on the following page of the printed handbook (page 298), outside this chapter extract.