Wet Scrubber Maintenance Checklist: Daily, Weekly, and Monthly Tasks
A wet scrubber maintenance checklist is a structured list of inspection tasks organized by frequency — daily, weekly, and monthly — that operators and technicians follow to verify the scrubber is operating within its design parameters. The daily checklist covers the five critical parameters that catch 80 percent of developing problems: recirculation pH, scrubber differential pressure, recirculation flow rate, sump level, and exhaust stack visibility. The weekly checklist adds instrument verification and pump condition checks. The monthly checklist requires a 2 to 3 hour internal inspection of the packing, nozzles, mist eliminator, and FRP/PP shell surfaces. Using a standardized wet scrubber maintenance checklist ensures that every operator checks the same parameters at the same intervals with the same pass/fail criteria, eliminating the variation between operators who “know what to look for” and those who miss early warning signs. This guide provides the formatted checklist templates for each frequency, implementation guidance for training operators, and digital versus paper checklist options for CMMS integration. For the full maintenance schedule and cost data, see our industrial scrubber maintenance guide.
Key Takeaways
- A standardized wet scrubber maintenance checklist eliminates operator variability — every operator checks the same parameters (pH, ΔP, flow, level, stack) at the same intervals with the same pass/fail criteria. Without a checklist, operators develop individual habits that miss different early warning signs.
- The daily checklist takes 15 minutes per scrubber and covers the five critical parameters that catch 80 percent of developing problems. The weekly checklist adds 10 minutes for instrument checks. The monthly checklist requires a 2 to 3 hour internal inspection during a brief shutdown.
- Each checklist item must have a clear pass/fail criterion — for example: pH 8-10 is pass, pH below 7 is fail. Subjective criteria like “pH looks normal” lead to missed problems. The checklist must quantify every parameter with a target range.
- Checklists must be signed and dated by the operator and reviewed by a supervisor weekly — a signed checklist is a legal document that demonstrates regulatory compliance. Unsigned checklists are not defensible during an EPA or OSHA inspection.
- Digital checklists in a CMMS system provide automatic trending and alarming — when a pH reading trends downward over three consecutive shifts, the CMMS can alert the supervisor before the pH reaches the fail threshold. Paper checklists require manual trend review that often gets skipped.
Daily Start-Up Checklist (15 Minutes)
The daily start-up checklist is performed at the beginning of each shift and takes 15 minutes per scrubber. The operator follows the same sequence every day to build a routine that makes it unlikely any step will be missed. Step 1 — verify the scrubber is in service and the fan is running. Check the exhaust fan amperage on the motor control center — the amperage should be within ±5 percent of the nameplate full-load amperage for the current operating conditions. A significant deviation indicates a fan or motor issue that must be investigated before proceeding. Step 2 — visually inspect the recirculation pump pressure gauge. The pump discharge pressure should be within ±10 percent of the design pressure at the design flow rate. A pressure decrease of more than 10 percent indicates nozzle blockage, pump wear, or a suction-side issue. A pressure increase indicates a discharge-side blockage. Step 3 — check the sump liquid level through the sight glass. The level should be at the normal operating level marked on the sight glass (typically 60 to 80 percent of the sump height). If the level is low, check the fresh water makeup valve and verify there is no leak in the recirculation piping. If the level is high, check the automatic bleed valve and verify it is not stuck closed.
Step 4 — read and log the recirculation pH from the inline pH probe display. The target pH range should be posted on the checklist (for example, pH 8 to 10 for a caustic scrubber removing HCl or H₂S). If the pH is within range, proceed. If the pH is below the target range (acid breakthrough), immediately check the caustic feed pump operation and the caustic tank level, and manually add caustic to bring the pH back to the target range. Document the corrective action taken and notify the shift supervisor. Step 5 — read and log the scrubber differential pressure from the DP transmitter display. The baseline value should be posted on the checklist (for example, 5.0 in. W.G. ±1.0 in. W.G.). If the DP is within the acceptable range, proceed. If the DP is more than 2.0 in. W.G. above the baseline, the packing may be fouling — schedule a packing inspection during the next monthly shutdown. If the DP is more than 1.0 in. W.G. below the baseline, there may be gas bypassing the packing — enter the scrubber at the next opportunity to inspect the packing bed for channeling or support plate damage. Step 6 — do a visual check of the exhaust stack. Look for visible mist or emissions at the stack outlet. Any visible plume during normal operation indicates mist eliminator damage, chemical breakthrough, or flooding — whichever it is, it requires immediate investigation. A clear stack is the best indicator that all upstream systems are functioning correctly. Step 7 — initial the checklist form with the date, time, and your signature. A checklist that is not signed has not been completed. A checklist that is signed without actually performing the checks is falsification that can result in regulatory penalties and personal liability if an incident occurs.
Daily Operating Log and Weekly Verification Checklist
Daily Operating Log (5 Minutes per Reading)
The daily operating log is a written record of the key operating parameters taken at the same time each shift. The log includes: recirculation pH (logged from the pH probe display), scrubber differential pressure (from the DP transmitter), recirculation flow rate (from the flow meter), pump discharge pressure (from the pump pressure gauge), motor amperage (from the MCC display), sump level (from the sight glass), and caustic feed tank level (from the tank level gauge or sight glass). Each reading is entered with a target range shown on the log sheet. Readings outside the target range are circled in red and initialed by the operator, with a corrective action noted. The log sheet has a column for “trend notes” where the operator records any observations about changes from previous shifts — “pH trending down from 9.2 yesterday to 8.6 today” or “DP has increased 0.3 in. W.G. over the past week.” These trend notes are the most valuable part of the log because they capture developing problems before they reach the fail threshold. The log sheet is placed in a binder at the scrubber control panel and reviewed by the shift supervisor at the end of each week. A weekly review of the trend notes takes 15 to 20 minutes and identifies 80 percent of developing problems 2 to 4 weeks before they would be caught by the pass/fail criteria alone.
Weekly Verification Checklist (10 Minutes)
Once per week, the operator performs the weekly verification in addition to the daily checklist. The weekly verification adds four tasks. Task 1 — verify the inline pH probe accuracy by comparing the probe reading to a handheld pH meter with a fresh two-point calibration (pH 4 and pH 7 buffers). The inline probe and the handheld meter must agree within ±0.5 pH units. If the difference is more than 0.5 pH units, the inline probe must be removed, cleaned with a mild acid wash (5 percent HCl or 10 percent citric acid), and recalibrated. Record the as-found and as-left readings. Task 2 — zero-check the differential pressure transmitter by closing both manifold valves (the high-side and low-side valves at the transmitter) and verifying the transmitter output reads zero ±0.1 in. W.G. If the transmitter reads more than 0.5 in. W.G. with both valves closed, the sensor diaphragm has drifted and the transmitter must be replaced — do not attempt to zero-adjust a transmitter with a confirmed sensor drift. Task 3 — listen to the recirculation pump with a mechanic’s stethoscope or screwdriver placed on the pump bearing housing. A smooth whirring sound is normal. A rumbling or grinding sound indicates bearing wear — schedule bearing replacement within 500 operating hours. A clicking or knocking sound indicates cavitation or impeller contact. Task 4 — check the caustic feed pump check valve operation by feeling the discharge line for the brief temperature rise that occurs when the pump cycles on. If the discharge line is hot continuously, the check valve is stuck open and scrubbing solution is backflowing into the caustic tank. If the discharge line never gets warm, the check valve is stuck closed and no caustic is being fed. A caustic feed system with a stuck check valve must be repaired within 24 hours because the scrubber will experience acid breakthrough within 4 to 8 hours of the caustic feed stopping. Per OSHA 29 CFR 1910.94, exhaust ventilation systems serving hazardous processes must maintain design airflow and performance at all times — the daily and weekly checklists are the first line of defense for compliance.
Monthly Internal Inspection Checklist (2 to 3 Hours)
The monthly internal inspection requires a brief scrubber shutdown of 2 to 3 hours. The operator locks out the fan and the recirculation pump, enters the scrubber through the manway with appropriate PPE (chemical-resistant suit, rubber boots, and a supplied-air respirator), and works through the following checklist items in order. Item 1 — packing surface condition: visually inspect the top surface of the packed bed. Look for solids accumulation (a thin even coating less than 2 mm thick is normal), scaling (white or gray hard deposits that indicate chemical reaction byproduct precipitation), and biological growth (green or brown slime, more common in scrubbers that handle organic compounds or operate at 30 to 40°C). If the fouling layer exceeds 5 mm thickness on more than 20 percent of the packing surface, schedule a packing wash or replacement within 30 days. Item 2 — liquid distribution nozzles: visually inspect the spray pattern from the top access door or sight glass while the recirculation pump is running (perform this step before locking out the pump). Each nozzle should produce a uniform cone-shaped spray pattern. A nozzle that produces a stream instead of a cone, or that is clearly dripping rather than spraying, is partially or fully blocked. Note the nozzle location for replacement during the next quarterly maintenance. The wet scrubber maintenance checklist should include a sketch of the nozzle layout with each nozzle identified by number, so the operator can mark the exact location of a blocked nozzle.
Item 3 — mist eliminator condition: visually inspect the mist eliminator vanes or wire mesh from the downstream access door. Look for solids buildup (white or gray deposits on the vane surfaces reduce the open area and increase pressure drop), corrosion or tearing of the wire mesh, and gaps between the mist eliminator frame and the scrubber wall that allow gas to bypass the mist eliminator. If solids buildup covers more than 30 percent of the vane surface area, wash the mist eliminator with water at 60 to 80°C through the dedicated wash nozzles or by hose access through the manway. Item 4 — FRP/PP internal surfaces: inspect the internal shell surfaces for blistering — small bubbles (1 to 5 mm diameter) on the FRP surface. Isolated blisters (fewer than 10 per square foot) under 5 mm diameter are acceptable. Blisters exceeding 10 per square foot or any blister larger than 5 mm require corrosion barrier repair at the next annual shutdown. Look for fiber exposure on FRP surfaces — visible glass fibers indicate the corrosion barrier has been penetrated, requiring immediate repair because the structural laminate loses strength at 5 to 10 percent per month once the fibers are exposed. Item 5 — sump condition: inspect the bottom of the sump for sludge accumulation through the sump drain or manway. Sludge depth exceeding 6 inches reduces the effective sump volume and can be drawn into the recirculation pump suction, causing pump wear and nozzle blockage. Document all findings on the monthly inspection form with photographs for comparison with the next month’s inspection. Each photographed defect should include a reference object (a coin or a ruler) to show the scale of the defect, and the location within the scrubber must be noted to track whether the defect is growing over time.
Printable Checklist Templates
The three checklist templates below can be copied, printed, and used directly at any chemical scrubber installation. Each template includes the pass/fail criteria and corrective action for each item — fill in the scrubber-specific target values (pH range, baseline ΔP, design flow rate) before printing.
Daily Start-Up Checklist
Shift: ___ Date: ___ Operator: ___
1. Fan running? Check amperage at MCC: ___ A (target: design FLA ±5%) ❐ Pass ❐ Fail
2. Pump discharge pressure: ___ psi (target: design ±10%) ❐ Pass ❐ Fail
3. Sump level at normal operating mark? (60-80% of sight glass) ❐ Pass ❐ Fail
4. Recirculation pH: ___ (target: 8-10 for caustic scrubber) ❐ Pass ❐ Fail
— If pH below 7: notify supervisor, check caustic feed, add caustic manually
5. Scrubber ΔP: ___ in. W.G. (baseline: ___ ±1.0 in. W.G.) ❐ Pass ❐ Fail
— If ΔP >2.0 above baseline: schedule packing inspection at next shutdown
6. Exhaust stack: visible emissions? ❐ None ❐ Visible ❐ If visible: shut down and investigate
Operator signature: ___ Corrective actions: ___
Weekly Verification Checklist
Date: ___ Operator: ___
1. Inline pH vs handheld meter: inline ___ handheld ___ Difference: ___ (max 0.5 pH units) ❐ Pass ❐ Fail
— If difference >0.5: clean and recalibrate inline probe. As-left inline reading: ___
2. ΔP transmitter zero check: close manifold valves, read: ___ (target 0 ±0.1 in. W.G.) ❐ Pass ❐ Fail
3. Recirculation pump sound: ❐ Normal (smooth whirring) ❐ Abnormal (grinding/cavitation)
— If abnormal: schedule bearing inspection within 500 operating hours
4. Caustic feed check valve: ❐ Normal (temperature rises briefly when pump cycles) ❐ Stuck open/closed
— If stuck: repair within 24 hours — acid breakthrough risk
Operator signature: ___ Supervisor review: ___
Monthly Internal Inspection Checklist
Date: ___ Inspector: ___ Shutdown start/end: ___/___
1. Packing surface condition: ❐ Clean (<2mm coating) ❐ Fouled (>5mm on >20% of surface) ❐ Scheduled cleaning date: ___
2. Nozzle spray pattern (check before pump shutdown): ❐ All uniform cones ❐ ___ nozzles blocked (mark on layout sketch)
3. Mist eliminator condition: ❐ Clean (<30% buildup) ❐ Fouled (>30%) ❐ Damaged/tearing ❐ Bypass gaps at wall
4. FRP/PP internal surfaces: ❐ No blisters ❐ Blisters <10/ft², <5mm ❐ Blisters >10/ft² or >5mm — schedule repair
5. FRP fiber exposure: ❐ None ❐ Glass fibers visible — immediate repair required
6. Sump sludge depth: ___ inches (max 6 inches before pump suction risk) ❐ Pass ❐ Fail
7. Photographs taken of defects with reference object: ❐ Yes ❐ No
Inspector signature: ___ Corrective actions: ___
Each template must be printed on paper that is durable enough to survive the scrubber area environment — use waterproof paper or plastic sheet protectors for checklists kept at the scrubber panel. Completed checklists are filed in a three-ring binder at the scrubber panel for the current and previous 12 months, then transferred to central records. For digital versions of these templates compatible with common CMMS platforms, contact XICHENG EP LTD. For the complete maintenance schedule that defines when each checklist item triggers a maintenance action, see our industrial scrubber maintenance guide.
Checklist Implementation: Training, Compliance, and CMMS Integration
Operator Training
A checklist is only effective if operators are trained to use it correctly. Training must cover three aspects. First, why each checklist item matters — operators who understand that a pH drop below 7 means acid breakthrough that damages the packing and shell are more likely to take the reading seriously than operators who think “pH is just a number to write down.” Second, how to recognize normal vs abnormal readings — operators must spend their first month working alongside an experienced operator who can show them what a normal pump sound, a normal spray pattern, and a normal stack appearance look like. Third, what to do when a reading is out of range — each checklist item should have a corrective action printed next to the pass/fail criteria. The corrective action for “pH below 7” should state: “Notifiy supervisor immediately. Check caustic feed pump and tank level. Manually add caustic until pH returns to 8-10.” The initial training session takes 4 to 8 hours, followed by supervised on-the-job training for 2 to 4 weeks until the operator can complete the checklist independently.
Compliance and Record Keeping
Completed checklists must be signed and dated by the operator, reviewed by the shift supervisor weekly, and filed for a minimum of 3 years per EPA and OSHA record-keeping requirements. The checklist binder at each scrubber must contain the current month’s checklists plus the previous 12 months for trend review. Older checklists are filed in a central records room or scanned into the CMMS. A completed checklist that shows a reading out of range with no corrective action noted is a red flag during an EPA or OSHA inspection — the inspector will question why the out-of-range reading was not addressed. A checklist that is missing entirely for a period when the scrubber was operating is a compliance violation. The shift supervisor’s weekly review must include a search for incomplete checklists and out-of-range readings that were not followed up. The supervisor initials each week’s checklists and follows up on any open items. The annual maintenance budget must include 10 minutes per operator per shift for checklist completion — for a facility with 3 shifts and 5 scrubbers, the daily checklist time is 3 shifts × 5 scrubbers × 15 minutes = 3.75 hours per day, or 1,370 hours per year. At $30/hour operator labor, the annual cost of running the checklist program is $41,100 — which is 2 to 4 percent of the cost of a single unplanned scrubber failure.
Digital vs Paper Checklists
Paper checklists are the lowest-cost option — a printed form in a binder with a pen on a string costs $5 to $10 per scrubber. Paper checklists require manual data entry for trending and are susceptible to being lost or damaged. Digital checklists on a tablet or mobile device cost $2,000 to $5,000 for the CMMS software license plus $500 to $1,000 per tablet. Digital checklists provide automatic trending of all parameters, automatic alerts when readings approach the fail threshold, photo documentation capability, and electronic signature compliance. The payback period for a digital checklist system at a facility with 5 scrubbers is 12 to 18 months based on labor savings from automated data entry and reduced troubleshooting time from trend analysis. Most facilities use paper checklists initially and transition to digital when the CMMS is implemented. For the complete maintenance schedule and budget data, see our industrial scrubber maintenance guide.
How to Handle Out-of-Range Checklist Readings
Every wet scrubber maintenance checklist item has a pass/fail criterion, but knowing what to do when a reading is out of range is as important as taking the reading. The following action guide covers the five most common out-of-range conditions. Condition 1 — pH below target range (acid breakthrough). Cause: caustic feed pump failure, caustic tank empty, pH controller malfunction, or inlet acid concentration higher than design. Immediate action: switch to manual caustic feed by opening the manual bypass valve on the caustic feed line. Confirm the pH starts rising within 5 minutes of manual feed. If it does not, the caustic concentration in the tank may be too low, or the inlet acid load is exceeding the scrubber capacity — reduce the process gas flow if possible. Notify the shift supervisor and log all actions. Condition 2 — scrubber ΔP more than 2.0 in. W.G. above baseline. Cause: packing fouling from solids accumulation, biological growth, or chemical scaling; mist eliminator blockage; or liquid flooding from excessive recirculation flow. Immediate action: check the recirculation flow rate. If flow is above design, reduce to the design flow and see if ΔP drops within 30 minutes. If flow is at design, the packing or mist eliminator is fouled — schedule an internal inspection within 7 days. Do not attempt to operate the scrubber at high ΔP by increasing the fan speed — doing so can collapse the packing support plate or damage the mist eliminator. Condition 3 — visible emissions at the stack. Cause: mist eliminator damage, liquid flooding exceeding the mist eliminator capacity, chemical breakthrough, or foaming in the sump. Immediate action: shut down the process gas source to the scrubber within 5 minutes. Continue running the recirculation pump and fan to clear any residual gas in the scrubber. Investigate the root cause before restarting — operating with visible emissions is a violation of the facility’s air permit. Condition 4 — recirculation flow rate more than 15 percent below design. Cause: pump strainer blockage, pump impeller damage, suction-side air leak, or partially closed isolation valve. Immediate action: check the pump strainer differential pressure — if it is higher than normal, clean the strainer and restart the pump. If the strainer is clean, check the pump motor amperage — a pump with a damaged impeller draws 10 to 30 percent less amperage than normal. If the amperage is low, schedule an impeller inspection during the next shutdown. Condition 5 — sump level continuously rising or falling. Rising level: automatic bleed valve stuck closed, fresh water makeup valve stuck open, or rainwater ingress through the stack. Falling level: leak in the recirculation piping, bleed valve stuck open, or a hole in the sump wall. For a rising level, close the manual makeup water valve and see if the level stabilizes. For a falling level, perform a visual inspection of the recirculation piping and sump exterior for leaks — a leak of 1 GPM from a pinhole in the recirculation pipe causes the sump level to drop by 2 to 4 inches per hour depending on the sump size. Each of these five conditions has a documented corrective action that must be taken before the next shift begins. The operator initials the wet scrubber maintenance checklist to confirm the corrective action was taken, and the shift supervisor verifies the system has returned to normal operation before signing off on the checklist.
Wet Scrubber Maintenance Checklist FAQ
What is a wet scrubber maintenance checklist?
A structured list of inspection and verification tasks organized by frequency — daily, weekly, monthly — with quantified pass/fail criteria for each parameter. The wet scrubber maintenance checklist ensures every operator checks the same parameters at the same intervals. The daily checklist takes 15 minutes and covers pH, differential pressure, flow, sump level, and stack visibility.
What parameters are checked on the daily wet scrubber maintenance checklist?
Recirculation pH (target 8-10 for caustic scrubbers), scrubber differential pressure (baseline ±1.0 in. W.G.), recirculation flow rate (design ±10 percent), sump level (60-80 percent of normal), pump discharge pressure (design ±10 percent), and exhaust stack visibility (no visible emissions). Each parameter has a pass/fail criterion and a corrective action printed on the checklist form.
How often should the pH probe be verified?
Weekly — compare the inline pH probe reading to a handheld pH meter with fresh two-point calibration (pH 4 and pH 7 buffers). The two readings must agree within ±0.5 pH units. If not, clean and recalibrate the inline probe. Replace the probe if it cannot be calibrated within ±0.2 pH units of the buffer values. Probe life in chemical scrubber service is typically 6 to 12 months.
What is checked during the monthly internal inspection?
Packing surface condition (fouling thickness <5 mm), nozzle spray pattern (uniform cone with no blocked orifices), mist eliminator condition (solids buildup <30 percent of vane area), FRP/PP shell surfaces (blisters <10/ft² and <5 mm diameter, no fiber exposure), and sump sludge depth (<6 inches). The inspector documents findings with photographs that include a reference object for scale.
How should completed checklists be stored?
Signed and dated checklists must be retained for minimum 3 years per EPA/OSHA requirements. Current month plus previous 12 months kept at the scrubber panel in a three-ring binder. Older checklists transferred to central records or scanned into the CMMS. Weekly supervisor review is required with initials on each week’s checklists to confirm review was performed.
What are the benefits of digital wet scrubber maintenance checklists over paper?
Automatic trending and alerting when readings approach the fail threshold, photo documentation with automatic date/time stamping, electronic signatures for compliance, and reduced data entry labor. The payback period for a digital CMMS system at a facility with 5 scrubbers is 12 to 18 months. Paper checklists cost $5-10 per scrubber but require manual trend review that is often skipped during busy shifts.
What corrective action should be taken if the wet scrubber maintenance checklist shows a failed item?
The corrective action is printed on the checklist next to each pass/fail criterion. For pH below 7: notify supervisor immediately, check caustic feed pump and tank level, manually add caustic until pH returns to target. For ΔP above 2.0 in. W.G. over baseline: schedule packing inspection. For any visible stack emission: shut down the scrubber and investigate the root cause before restarting.
Who reviews the completed wet scrubber maintenance checklists?
The shift supervisor reviews the previous week’s checklists weekly, looking for incomplete entries, out-of-range readings without corrective actions, and trends in readings that may indicate developing problems. The supervisor initials each week’s checklists. The completed checklists are filed for the required retention period and are available for review by EPA or OSHA inspectors during site visits.
A wet scrubber maintenance checklist ensures every operator checks the same parameters at the same intervals with the same pass/fail criteria. The daily checklist covers pH, ΔP, flow, level, and stack visibility in 15 minutes. The weekly checklist adds instrument verification and pump checks. The monthly checklist requires a 2 to 3 hour internal inspection of packing, nozzles, and FRP/PP surfaces. Completed checklists must be signed, reviewed by supervisors weekly, and retained for 3 years. Digital checklists provide automated trending for 12 to 18 month payback. For the full maintenance schedule and budget data, see our industrial scrubber maintenance guide.