Drum Plant Winter Maintenance Checklist Part 1

Another winter is nearly here. With the paving season drawing to a close many companies’ thoughts are turning toward a winter repair regimen for their asphalt plants. It’s no secret in our industry that what you do to your plant in the off-season bears heavily on your success during the next paving season.

Most asphalt plant operators have a list of ‘trouble spots’ they’ve accumulated over the course of the season, but things are often overlooked when they’ve been trouble free. It’s that old ‘outa sight, outa mind’ trap we all fall into occasionally. A thorough AC plant checklist, strictly adhered to, can go a long way toward assuring that no items are inadvertently neglected.

What follows is the author’s inspection checklist, developed over 25 seasons of involvement with numerous asphalt plants in various parts of this country and Canada. This first part will deal with drum-mix plants and the components used on both a batch plant and a drum plant. In PART 2, we will talk about batching towers and their special needs.

NOTE: The author is by no means familiar with every possible combination of equipment used on contemporary asphalt plants. Omissions are bound to happen. Keep in mind that this article is intended as a suggested guideline to help minimize surprises in the coming paving season.

These inspections are done with pen and paper in hand. No repairs are made at this time. The purpose of this activity is to formulate a list of observed problems and to facilitate the creation of a strategy to address them. A can of orange ‘marking paint’ is handy to tag components slated for later repair.

Every component should be made safe as per OSHA lockout, tag out regulations prior to inspection. On particularly dangerous units the author will include a reminder.

COLD FEEDS: The feeders should be emptied of all aggregates for this inspection.

1- Check the bin walls in each feeder. Thin or damaged areas should be marked for repair. Excessive scaling should be noted for removal as it interferes with consistent aggregate flow and can contribute to feeder stoppages. Also check the bin dividers. Mark for repair any damaged or missing components.

2- Check each bin’s flow gate and the mechanism by which it is lowered and raised. They should move freely and lock into place with a minimum of fuss. Poorly maintained gates often lead to excessive downtime when it is necessary to make feeder adjustments and the operator discovers that nothing short of dynamite will move a bent or corroded gate. At the least, the gates and their guide rails should be cleaned and the operating mechanism lubricated.

3- Check the seal skirting around each feeder for excessive wear and note any needed repairs. Pay particular attention to what effect the skirting is having on the belt it seals. If deep ragged grooves exist where the seal contacts the belting it is possible that the larger aggregate sizes are binding under the skirting or its supporting metal and are being forced through the conveyor belt’s cover. This is a highly undesirable condition and should be noted for correction.

4- A detailed inspection of each individual feeder belt is next. Check for excessive wear, weather checking and any brittle or damaged sections. Examine the area where the skirting rides. If the belt is worn into the cords in these areas perhaps it’s time for a new belt. Also check the edges of the belting. Sometimes tracking problems can seriously damage the belt, requiring repair or replacement.

No matter what kind of belt lacing is used it should receive an exacting examination. Worn and broken components are a liability. If in doubt, mark them for replacement. Keep in mind that it’s much easier to fix the belt under an empty feeder than one under a full feeder, especially when the trucks are stacking up and time is being lost with the paving crew idle.

5- A systematic examination of each feeder belt’s bearings follows. Use a bar and pry the head and tail shafts around. Mark for replacement any bearing that exhibits excessive movement. The same criteria applies to the troughing and support rollers. Any damaged components should be marked for repair.

6- Remove the guards and inspect each feeder’s drive system. Chain drives suffer large amounts of wear in the hostile environment around the feeders. If your units use this method of propulsion it is important that you inspect the chains for excessive wear and each sprocket for signs of damage. Look for a condition called ‘fish eyeing’, or cupping on the load side of the teeth. Mark any abnormalities you find.

If your feeders are belt driven you need to look for cracked or glazed belts, excessively worn sheaves and a loose condition which requires adjustment.

For mechanical variable speed drives, the inspection covers should be removed and the condition of the drive belt and sheaves checked.

7- Flow alarms should be tested for proper operation. These little guys can be life savers when you are making tight spec mixes or working on a ‘pay-factor’.

8- All bin vibrators or air-cannons should be inspected for damage and tested for operation at this time. One way to do this if they work off your flow alarms is to disconnect the feeder drive chain (or belt), defeat the conveyor interlocks and turn the feeders on. If the system works the cannons or vibrators will come on. If they don’t, mark them for repair.

9- On portable feeders, inspect the tires, brake components, springs and lights. A thorough examination of the brakes and lights should be scheduled with your mechanic at a later time. For now your goal is to note the obvious. This applies to each unit on a portable plant and will not be mentioned again.

10- Any mechanical leveling or jacking devices should receive special attention at this time. When these components work they can drastically reduce the amount of time needed to set up the feeders after a move. This also applies to the baghouse, the oil tanks and to any other unit utilizing these features.

11- Inspect all wiring. Mark for replacement any lead that is doubtful. This is a safety issue and could possibly avert an injury. It is also a good idea to inspect all motor grounds for proper connection.

See the GENERAL MAINTENANCE section near the end of this article.

COLLECTING CONVEYOR:

1- Inspection of this component is similar to the feeder belts. Check for excessive wear, weather checking and any damaged areas. Again, check the edges of the belting. Tracking problems are usually more pronounced on the collecting conveyor. Mark excessive damage for repair or replacement. As with the feeders, the belt lacing should receive an exacting examination. Worn and broken components are a liability. If in doubt, mark them for replacement. Keep in mind that a broken collecting conveyor belt can lead to prodigious piles of aggregate which require much time and effort to remove by hand.

2- Examine the conveyor’s bearings. Again, use a bar and pry the head and tail shafts around. Mark for replacement any bearing that exhibits excessive movement. Check the troughing and return rollers. Any damaged components should be marked for repair.

3- Remove the guard and inspect the conveyor’s drive system. If you have chain drives, examine each sprocket for ‘fish eyeing’, marking any abnormalities you find.

For belt drives you need to look for cracked or glazed belts, excessively worn sheaves and a loose condition which requires adjustment.

4- Check the condition of the belt wiper, noting any repairs needed.

See the GENERAL MAINTENANCE section near the end of this article.

Important: Reinstall all guards if there is any chance your plant might run before repairs are made.

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NOTE: SKIP AHEAD TO SCALPING SCREEN IF YOU DON’T HAVE A LIME/CONCRETE SILO AND PUG-MILL.

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LIME/CONCRETE SILO:

The silo should be emptied for this inspection and all power locked out and tagged out.

1- Inspect the general area around the silo. Is there lime/concrete scattered about? If so, you need to find the leaks and mark them for repair. One area of concern is the small baghouse on top of the silo. (not all units have this feature) Inspect it for faulty bags, poor seals and smashed metal which is common on upright silos where the baghouse is removed to facilitate transport. 

2- Examine the silo’s vane feeder closely. Look for accretions of solidified lime/concrete that can interfere with proper operation of safety gates and cause binding of the feeder. Check the drive system for signs of wear and mark for repair anything that raises doubts in your mind.

3- Inspect the air fluffing system. Look for frayed or damaged hoses, missing clamps, damaged or inoperative control solenoid, etc. Pay close attention to the air ‘drier’. Moist air blown into a concrete silo can lead to major headaches later.

LIME/CONCRETE AUGER:

1- Inspect the lime/concrete auger. Look for worn flights or a thin bottom. Use a bar to pry bearings about and mark for replacement any found to be excessively loose.

2- Examine drive system and note any abnormalities. Check for a build-up of lime/concrete in the drive motor’s cooling fins. This condition often leads to premature motor failure. Mark for clean-up if needed.

3- Check the fit of the auger’s covers. Mark for repair any that need attention.

See the GENERAL MAINTENANCE section near the end of this article.

LIME/CONCRETE RATIO SYSTEM:

Consult the factory manual for whatever device you have and follow their recommendations for inspection and periodic maintenance.

PUGMILL: Follow OSHA Lockout-Tag out regulations before inspecting this potentially lethal unit.

1- Remove the lids and examine the interior of the unit. Look for excessively worn shanks, tips and liners. Cracked or broken components should be slated for immediate replacement.

2- Examine the mainshaft bearings. Again, use a bar to pry the shafts around. Mark for replacement any bearing you are in doubt about.

3- Inspect the drive assembly. With chains, look for ‘fish-eyeing’ and excessive wear. For belt drives look for the same things as on the feeders. Special attention should be given to those units that use shaft couplers. Check for any signs of damage or movement. Again, when it doubt replace them. Failure of one of these devices on certain pugmills can throw the timing off, resulting in catastrophic damage to the machine.

4- Check the wiring for any condition that could render it unsafe. Mark anything that is substandard.

See the GENERAL MAINTENANCE section near the end of this article.

SCALPING SCREEN:

1- Inspect the condition of the screen cloth. Look for the obvious: Excessive wear, broken or missing wire, or wire cracking- especially around the edges where the mount bars are.

NOTE: It’s a good idea to have a spare screen on hand regardless of the condition of the one on the machine.

2- Check the vibratory shaft bearings. Again, use a bar to pry these units around. Replace any which exhibit excessive movement or roughness.

3- Check all the support springs. Look for broken, missing or excessively worn components. One thing to keep in mind: spare springs, stored in your parts inventory, could well prevent downtime in the event of a spring failure on some future date.
4- Inspect the skirting between the screen and the conveyor it sits over. Leaks in this area can cause a build-up of aggregate which interferes with the operation of the tail roll of that conveyor.

5- Check the drive system and wiring, again looking for the same faults we’ve discussed on previous pieces of equipment.

SCALE BELT: The ratio computer is the brains and the scale conveyor is essentially the heart of a drum mix asphalt plant. Under certain conditions, if it is transmitting inaccurate data to the ratio computer, this unit can literally break a company through ‘out-of-spec’ penalties. Considering what is at stake, this unit deserves an exacting and painstaking inspection. Since the price of failure is so high, the old adage ‘when in doubt, throw it out!’ applies to the components of this unit more than any other.

1- Begin by inspecting this unit the same as for the conveyors we’ve previously discussed. Pay particular attention to any evidence of ‘tracking’ problems such as ragged or frayed belt edges. The scale conveyor’s frame sometimes offers testimony of tracking problems in the early stages. Look for shiny places on the frame around the head and tail roll areas which would indicate belt rubbing. Tracking can, and does, effect the data output from the weigh bridge.

2- Check the speed sensor (usually on the tail roll). Is it loose or damaged in any way? If so, slate it for attention. Pay close attention to the unit’s wiring. Is it damaged or brittle? If so, it should be replaced.

NOTE: It’s a good idea to have a spare speed sensor with new wire on hand should the unit fail in the heat of battle.

3- The weigh bridge should be checked for any obvious damage. Malfunctioning rollers on this unit cause inaccurate readings, leading to ‘out-of-spec’ mix. Additionally, three rollers above and below the weigh bridge should be examined exhaustively. Mark for repair any that raise questions. It is also a good idea to schedule an examination of the ride height of the weigh bridge. Usually this is done with a string line. Consult your unit’s operating manual for the proper procedure.

4- A visual inspection of the load-cell usually reveals little other than physical damage. These components either work or they don’t. For this reason it is strongly recommended that a functioning spare be kept on hand.

5- Schedule a time for a full scale belt calibration test sequence. You should check for ‘weighed load’ accuracy, linearity (accuracy through a wide range of weights) and repeatability. If the unit fails any of these tests do you want to head into a paving season with it?

See the GENERAL MAINTENANCE section near the end of this article.

SLINGER CONVEYOR OR FEED CHUTE: Some plants use chutes, others use conveyors to feed the cold aggregates into the drier. We’ll talk about chutes first, since it is a simple procedure to check it.

Chute:

1- Thoroughly clean the chute, then inspect the floor and walls for abnormal wear. Record any repairs that are needed.

Slinger belt:

Because of its high operating speed a slinger conveyor, especially a reversible one, requires a more thorough inspection than a normal conveyor.

1- As with the other conveyors, check all bearings and rollers.

2- Since this unit typically runs under the burner, you need to check the belt for any signs of heat damage. If there is any doubt in your mind about this belt REPLACE IT! In the case of vulcanized belts this is a time consuming process, not one you want to address in the middle of a large paving job. If yours is a laced belt and shows signs of damage, perhaps it would be a good idea to stock a pre-cut and laced spare so that replacement time is reduced to a minimum.

3- Bearings at the burner end of the slinger conveyor operate in an extremely hostile environment. High heat combined with high speed ensure that these units are a frequent maintenance item. A few spare bearings could spell the difference between down-time and nightly maintenance. If you don’t already use them, perhaps you should check into ‘hostile-duty’ bearings designed and introduced in recent years for just such applications.

4- Most slingers use ‘training’ idlers. Examine them to verify proper operation. Mark for repair or replacement any that need it.

See the GENERAL MAINTENANCE section near the end of this article.

DRIER/MIXER: Whole articles could be written on the subject of DRIER/MIXER maintenance, covering a wide variety of topics including flight design and internal air flow relating to veil patterns. That’s not the focus of this dissertation. We will deal with inspecting and scheduling repairs for the components that you already have. To that end, no mention will be made of the various configurations of flights that are available.

We will begin with the internal components of the unit, then move to the external components. Since the inspection detailed in #6 of the BURNER section is performed from inside the drier, perhaps it would be a good idea to read that section also before entering the drier.

The unit should be as clean as possible inside for this inspection. Before setting out on a manual cleaning mission, consider heating 20 or 30 tons of course aggregate to around 400 degrees. Sometimes this will clean a surprising amount of accumulated material out of a drum mixer, slat conveyor, batcher and storage silo.

1- Inspect each and every flight for the following problems:

A- excessive wear
B- heat curling
C- impact bending
D- cracking or absence

Mark for replacement any flight that exhibits these problems. Obviously, any that are cracked can probably be welded, and those that are missing must be replaced.

2- Examine the mounts for each flight, noting and marking any cracked or broken components.

3- While you are in the drier it is a good idea to have an assistant cover what openings he can with plywood. Extinguish your light and look for sources of light that shouldn’t exist. Pay particular attention to the knock-out box and its associated ductwork. These leaks reduce the amount of air available to the drying process, cause excessive burner fuel usage and, under certain conditions, leak dust into the atmosphere which can throw up a red flag at air quality inspection time.

4- Check the rakes at the mixer discharge. Note any bent or missing rakes.

5- Inspect the discharge collar, looking for worn-out liners. Also examine the upper end of the discharge chute.

6- Look at the oil injection tube. Is it wearing badly on top? Are there any holes or cracks? Mark for repair anything that is wrong. NOTE: On those units exhibiting wear on the top which is caused by cascading mix abrading the pipe perhaps you should consider installing a small trough on top of the injection pipe to catch a quantity of mix. On a three inch pipe, for instance, a four inch channel welded on with the upright sides of the U pointed skyward will quickly fill with hot mix. Since the mix is constantly being replaced as it wears away this operation will effectively end any future wear problems.

7- On plants with a recycle collar examine the inlet chute and the kicker flights. Look for excessive wear, missing parts or product build-up.

The external inspection of the drier/mixer follows.

1- Examine the drier barrel end seals at the inlet and discharge collars. These often overlooked components can contribute significantly to fuel efficiency if they are in good condition. If your plant has a recycle collar you should examine its seals also at this time.

2- On plants with inlet chutes, check the air dam and see that it seals off the area over the incoming aggregate. If it’s excessively worn, mark it for repair.

3- Examine the air dam in the discharge chute, noting any problems and marking them for repair.

4- Next are the drier trunnions. Examine each one for excessive wear or damage. To check the bearings it’s a good idea to jack the drum up and use a bar to pry the units around. Proper trunnion adjustment is very important to over-all drier operation. It’s difficult to maintain the proper settings with worn-out components so any loose bearings or abraded trunnions should be marked for immediate action.

5- On those units which use thrust bearings to control drier position you should examine them to be sure they are in good shape. Excessive contact can indicate improperly adjusted trunnions. If this is the case, schedule some time to make the necessary adjustments as-per factory instructions.

6- Drive methods vary from plant to plant. For chain driven units you should inspect for the same things as any other chain drive. On friction drive units the condition of the trunnions is more important. To avoid slippage they must be smooth and flat. On both drive styles you should check the condition of the gear boxes and any belts used.

7- On driers with a hydraulic jacking and leveling option begin by inspecting the power/pump unit. It should start easily and operate with a minimum of headaches. Hook the unit to each individual jacking station and check operation. On driers with screw jacks on the end of the set-up supports check each one for proper operation.

When moving and resetting the plant the previous devices can substantially reduce the amount of time the crane is on the job and as we all know, cranes are spendy.

See the GENERAL MAINTENANCE section near the end of this article.

RAP SYSTEM: On plants with this option the inspection procedure is, essentially, the same as for the cold feed system to the inlet to the drier. Follow those directions.
Remember to schedule a thorough calibration sequence for your scale belt.

SLAT CONVEYOR: Slat conveyors can be unforgiving, lethal units if not treated with respect. Before beginning this inspection follow OSHA Lock-out, Tag-out regulations.

1- Inspect the condition of the floor, the flights and the chain. Obviously, the most important consideration here is whether or not they will operate trouble free for the amount of tonnage you expect for the next season. Will the floor develop leaks? Are any chain links in danger of failing? How about the flights? Are they excessively worn, unable to carry a full load thus contributing to a floor build-up which could lead to stalling? These are judgment calls, but it is a good idea to remember how hard it is to dig 300 degree mix out of a stalled or broken slat conveyor. This is one of those places where the philosophy ‘if in doubt, throw it out’ could prevent a major shut down at an inappropriate time.

2- Inspect the main drive sprockets at the top of the slat. If worn, can they be turned? If not, mark them for replacement. Don’t take chances on these guys. If they’re segmented sprockets then they’re relatively inexpensive and easy to replace. If they’re not, do you really want to tackle changing them in the middle of a paving contract?

3- Examine the reject gate. Look for excessive wear, misalignment which causes leakage or any other condition causing a poor seal.

4- Inspect the reject gate’s air actuation system. Look for frayed or cracked air hoses, excessively worn air cylinders and pivots. Check the system’s air solenoid and oiler. Do they work reliably? Perhaps a thorough cleaning and tune-up would be a good start?

See the GENERAL MAINTENANCE section near the end of this article.

ASPHALT HOLDING SILO:

Batcher: The batcher is one of the most important pieces of equipment on an AC plant when it comes to battling mix segregation. As such it should be treated with a high degree of respect. Often, when this unit has problems, its gates are chained open and the job moves forward. Quality suffers, but the price of a shut-down for repairs to the batcher are deemed excessive and as long as the mix is accepted things go forward. With a little foresight, this whole scenario can be avoided.

1- Inspect the batcher’s sides and cone for thin spots. Mark for plating any you find.

2- Look closely at the gates and their pivots. Use a bar to pry the gates around. Are they loose? Have they been greased in the last decade? Mark for repairs any abnormalities you find.

3- Meticulously examine the air actuation system. Failures here are the primary cause of batcher problems. Check the air cylinder(s) for excessive wear. Substandard air hoses should be slated for replacement. A suggestion: Consider having spares made up and stored in a handy location. As with the reject chute controls, it’s a good idea to target the batcher’s air solenoid and oiler for a thorough cleaning and tune-up. Kits for these items are inexpensive and easy to install. It is highly recommended that you stock a spare solenoid at least, and an oiler if possible. With any luck at all, the solenoid and oiler for this unit are the same as the ones for the reject chute.

4- If your batcher uses ‘high-level’ indicators test them for proper operation. Refer to the factory manual for specific procedures. In general: If you have limit switches, activate them and have someone watch the appropriate warning light in the control room. If you have a torque stall type indicator, simply hold it from rotating and have someone check the light. Target for repair any system that fails to work. Over filled batchers are notorious for stalling slat conveyors. Choked to a halt under these conditions, the slat is usually full to the covers and quite simply a real bummer to clean out.

Holding silo:

The same inspection protocol is used for the holding silo as for the batcher.

1- Check the iron, especially in the cone area. Mark for repair or replacement any thin areas.

2- Again, the gate and all its actuating controls should be examined. Schedule the air solenoid and oiler for a cleaning and tune-up. And as with the other gates, a spare solenoid should be on hand. Spare air hoses can be time savers here too, should one fail in the heat of battle.

3- Get in a loader bucket (be sure to use an OSHA approved safety restraint belt) and have yourself hoisted up next to the gate. Check the pivot pins by prying the gates around with a bar. Schedule repairs for any found lacking. Look at the grease zerks. Have the pins seen a grease gun since leaving the factory? You might be surprised to find out how many haven’t.

4- Check the operation of the silo’s high and low warning alarms. Use the same procedures as with the batcher.

BURNER AND FUEL SYSTEM: Each burner manufacturer has written a maintenance manual for their specific product. Find that manual and study it. Following their recommendations might well avert a breakdown at an inopportune time.

In general and for older units:

1- It is absolutely essential to test and verify the operation of all safety systems. Accidents due to inoperable safeties can and do happen (Safety Articles).

2- Examine all fuel and propane lines. Schedule for replacement any that raise a question in your mind. Also look at the propane bottle for the igniter. Check for signs of leakage and damage.

3- Check the fuel pump and drive mechanism. Mark any frayed belts, worn couplers or leaking seals. Schedule the fuel filters for replacement, regardless of how long they’ve been in place. It’s cheap insurance.

4- Check the piping and valving from the supply tank. Now is a good time to verify that shut-offs do, in fact, work. Don’t take them for granted, it may come back to haunt you. Also take a minute and inspect the tank’s filling apparatus. Note any leaks or unsafe practices.

5- If your fuel system uses a water separator, consult the manufacturer’s literature on maintenance procedures. In general they should be drained and cleaned.

6- If you have a poured ignition port and combustion chamber they should be checked for signs of damage. These units are often easiest to check from inside the drier/mixer. Since these items can fail all at once sometimes following relatively minor damage, it’s best to schedule repairs on any area that raises questions in your mind.

EXHAUST FAN AND DUCTWORK:

Ductwork: This inspection is not for the claustrophobic. The ductwork can be a tight, confining area; not a place for a panic attack. If you’re up to it find a set of cover-alls, it’s time to get dirty.

1- Inspect the ductwork from the outside first. Look for loose or misaligned joints and any physical damage that might lead to an air leak. On portable plants with a wet wash you should check the seals around where the venturi enters the knockout-box and the scrubber. The same holds true for the ductwork between a baghouse and the knockout-box.

2- Double check to see that the exhaust fan is looked out and tagged out as per OSHA regulations. Once you’ve done that, crawl inside the ductwork and inspect it for any signs of damage. Mark anything that raises questions. Now turn off your light. Look for any source of light that shouldn’t exist. Obviously, these are leaks. Note any you find and mark them for repair.

3- Check for material build-up in the ductwork. Such accumulations often offer evidence of air flow deficiencies that should be analyzed and the root problem corrected in order to maximize plant efficiency and minimize fuel usage.

Exhaust fan: Many styles of fans are in use in contemporary AC plants. An entire article could be written on the pros and cons of each type. Since the focus of this discussion is maintenance the following checklist is general in nature.

1- Examine the fan for any signs of excessive wear. On paddle fans pay close attention to the hub area where the fan blades attach. Look for cracks that could be precursors for a catastrophic failure of the unit.

2- On wet fans look for excessive scale build-up which can lead to an out-of-balance condition that if left unaddressed can cause structural failure. Fan explosions are spectacular events to witness! They are also expensive.

After the fan is cleaned and no flaws are found, perhaps it’s a good idea to schedule a vibration analysis. Fan balancing companies can come to your facility, balance your fan and electronically examine the bearings, leaving you with a clear picture of your unit’s condition. We recommend that lower production facilities (under 100,000 tons per year) be tested every other year. For higher production operations yearly is a good choice unless the fan is exhibiting chronic balance problems.

NOTE: Wet fans presenting chronic balance problems due to a build-up of mud on the fan blades can sometimes be helped by the simple addition of a regulated water spray nozzle directed at the center of the fan on the inlet side. This washes away the accumulated mud and extends the life of a balancing job. Caution- only add as much water as needed to keep the fan clean since the excess simply goes out the stack as muddy rain. Done properly, you shouldn’t see any change in the stack.

3- Inspect the fan housing for worn and leaking areas. Mark any abnormalities.

4- Closely inspect the exhaust damper and its associated operating system, including the actuator. Mark for attention anything that raises questions in your mind.

5- Examine the fan motor, motor mount and belt guard. Anything catch your eye? Mark it for attention.

6 – Be sure the fan is locked out, then remove the belt guard. Examine the belts and sheaves. Excessive wear here reduces fan efficiency and can lead to belt burn-up when starting.

NOTE: It’s a good idea to carry spare belts for this unit, since new ones this size aren’t always readily available.

VENTURI WET WASH SYSTEMS:

1- Begin by examining the entire system from the outside. Look for muddy areas which indicate leaks. Mark these for attention.

2- Inspect the venturi actuator/positioner. This item is critical to the operation of the venturi/scrubber system. If you have any doubts about it, schedule it for maintenance.

3- Remove the venturi’s inspection door. You’ll have to crawl inside if your unit doesn’t have one. Look for worn components, bent or warped venturi plates and missing water nozzles. It’s recommended that all nozzles be scheduled for removal and cleaning. A spare set of nozzles is a good idea and also cheap insurance against the down time incurred while the operator tries to clear obstinate nozzles in the heat of battle.

4- Inspect the water feed system. Check the hoses, connections and the y-filter. (You do have a y-filter removing the stuff that plugs nozzles, don’t you?) Mark anything found to be substandard. The y-filter should be marked for a screen cleaning at a later date.

5- If you use a flow meter you should refer to its maintenance manual for advice on its upkeep.

6- Closely examine the water pump and its foot-valve. It’s a good idea to schedule someone to remove the impeller housing on the pump and inspect the impeller for excessive wear. Failure of the pump can shut an operation down for an extended period of time under certain conditions. A faulty foot-valve leads to delayed start-ups and wasted time while the plant crew tries to prime a stubborn pump.

7- Remove the wet-scrubber’s access door and climb inside. Is the unit muddy or relatively clean? Muddy scrubbers must be cleaned out. Excessive mud indicates that the scrubber is not working correctly. Analyze the situation and find out why. One cause could be low water volume. Another cause could be a partially plugged drain trough. Stubborn units often require the addition of a water nozzle in the head of the trough to wash particulates down and out into the settling ponds.

8- Examine the strike-off plate directly above the drain trough. Is it in good condition? If not, schedule it for attention.

9- Inspect the interior of the scrubber. Look for rusted out areas that could fail in the middle of a job. The supports for the fan inlet tube should be checked and marked if there is any doubt as to their structural integrity.

10- Often, people will install a screen over the tube leading to the fan inlet in a misguided attempt to catch large chunks of material before they are ingested by the fan. If your unit has such a screen REMOVE IT! This screen causes the formulation of water droplets, and leads directly to muddy rain from the stack. Again, remove it. The chances of the fan ingesting a chunk of foreign material large enough to cause any damage are minimal at best. This is especially true of a well maintained wet scrubber.

11- See item 10 in the BAGHOUSE section.

BAGHOUSE: Refer to the manufacturer’s maintenance manual for your specific unit prior to beginning this survey. The following checklist is general in nature.

NOTE: It is a good idea to use a powder test to locate leaking bags prior to this inspection.

1- Examine the baghouse from the outside first. Note any signs of damage. Look for leaking covers on top, disconnected solenoids or by-passed sections. Make notes on any deficiencies.

2- Most units are fitted with their own air compressor. Refer to the compressor’s manual for the yearly maintenance schedule. In general, the compressors should be serviced and all filters changed. Check all drive belts and air lines. This is another place where spares could mean the difference between a short break in production and early finish to a day. Worse case scenarios include days of down-time waiting for parts thought to be readily available but actually not.

3- Inspect all air lines. Look for cracking, heat damage, weather damage or anything that raises doubts. Schedule your air driers for cleaning. Mark damaged ones for replacement. Examine the electronic controllers. If anything is by-passed or jumpered schedule repairs. The air solenoids should be checked for proper operation and any that fail scheduled for repair or replacement. Lastly, look at all the air cylinders. Mark any that raise questions.

4- On reverse air units check the doors, seals, actuating cylinders and solenoids. This is a time consuming job, but one that is necessary to insure the correct operation of these units.

5- Open the lids on top of the baghouse. Check the bag seals, cages and venturis if so equipped.

6- Modern baghouses use either augers, drag chains or a combination of the two to get rid of 200. On both units check the bearings and flights. On the drag chain you need to look at the chain and sprockets. You are looking for excessive wear and/or fish-eyeing of the sprockets. Schedule repairs for anything you find amiss.

7- Most baghouses use dust return systems to put the fines back into the DRIER/MIXER. These can be air pumps or augers. Check these units for excessive wear and for proper operation.

8- On systems using air pumps, check the air box and the hoses used to pump the fines to the drier.

9- Most baghouses use either a slam damper or a similar device to shut off air flow through the baghouse in the event of excessive heat. Check the operation of these safety devices. At times they are all that stand between you and a very expensive repair bill. Other safety devices such as temp monitors and pressure drop gauges are used. Check these for proper operation.

NOTE: See the MISCELLANEOUS section for information on calibrating your thermometers.

10- If your exhaust stack uses a profiler to straighten the air flow and correct stack cyclonics (require by DEQs in most states) you should examine it and its supports at this time. Look for corrosion and rust which could lead to the profiler falling into the bottom of the stack.

HEAT TRANSFER OIL SYSTEM: Two types of heat transfer oil heating systems are in use on today’s AC plants: Electric and oil fired. Some units are stand-alone, others have most of their components built into the AC oil storage tanks.
NOTE: This examination should be done on a cold system.

General:

1- Examine your unit’s overall condition. Has the control box been hit by one too many loaders, leaving the electrical components exposed to the elements and a hazard to anyone venturing near? Does the unit still have insulation? Is the unit clean, or is it covered with several years worth of accumulated crud? These are safety issues, and as such should be addressed accordingly.

2- Examine the hoses over the entire system. Are they brittle, cracked or leaking? Any that fit this description should be marked for replacement. Look at the oil pump. Is the seal leaking? Are the drive belts and guard in good condition?

3- Hot oil holding tanks have a low-level shut down device. Check to see that yours works properly.

4- Test the control temperature sensor to verify accuracy.

5- Also test the overtemp protection thermometer. This device can save lives and often does save dollars on burned out units caused by the failure of the primary control thermometer.

NOTE: See MISCELLANEOUS section for how to test thermometer bulbs.

6- It’s a good idea to have the heat-transfer fluid analyzed by a reputable company. It’s also wise to change the oil every couple of years. When’s the last time yours was changed?

7- Inspect and test the auto start system. Does the time clock keep accurate time? Does the unit start and stop at the appointed hours? Is it reliable?

Oil fired units:

1- Examine the fuel system. Check for leaking lines and seals. Schedule a fuel filter change.

2- Check the exhaust damper system for proper operation.

3- These units utilize several safeties similar to those found on your main burner, such as an ultraviolet ‘flame-eye’ which is used to detect burner combustion. The unit also uses a step timer to control things during the start-up/shut-down sequences. Refer to your operator’s manual for specific procedures for testing yours.

Electric units:

NOTE: Electrical shock hazard, disconnect the electricity before proceeding.

1- Examine the wiring and connections. Schedule repairs on any that are loose or corroded. Do you have spare fuses handy? How about the small fuses used on the control circuits? These little guys are often hidden and the plant operator is unaware that they exist until one fails and production grinds to a halt. It’s also a good idea to stock the contacts and a pull-in coil for the motor starter and for the heater relays.

ASPHALT OIL HOLDING AND DELIVERY SYSTEMS:

Pump pallet:

1- Check the general condition of the asphalt pump. Is the shaft seal leaking? The case gaskets? How about the pipe connections?

2- On belt driven units you should check the condition of the sheaves and belts. Is the guard in place and in good condition?

3- On hydraulic units it’s a good idea to schedule an oil and filter change. Also, examine the hoses, seals and the coupler between the pump and motor. If the unit is covered in grime, schedule a cleaning session paying particular attention to the oil cooler.

4- All units use some sort of flow indicator or tachometer to provide a signal to the ratio computer so that it can regulate the oil percentage. Given the value of these items to the plant’s overall success, it’s a good idea to pay close attention to them. A spare pick-up, drive belt or tachometer may keep a plant running and in spec in the event one of these units fail.

5- Examine the flex lines from the tank to the pump and from the pump to the drum. Mark for replacement any that are frayed, kinked or raise any questions in your mind.

AC oil holding tanks:

In general, you should examine the overall condition of the tanks. Is the insulation and covering skin in good condition? Are the tanks clean or are they covered with an accretion of oil? How about under the tanks, is there enough accumulated oil to throw up a red flag on DEQ inspection day? If you answered yes to the last two questions then perhaps it’s time for a serious cleaning regimen.

1- As with the heat transfer oil system, you should schedule testing to determine the accuracy of the AC tank’s temperature controls. NOTE: See MISCELLANEOUS section for how to test thermometer bulbs.

2- Check your tank vents to see that they are not plugged or obstructed.

3- Inspect the tanker off-loading pump and associated plumbing. Use the same protocols as for the pump pallet. One thing to look for: Oil haulers are known for starting and stopping pumps with their asphalt covered gloves on. Are your switch buttons gooed up to the point that they no longer function properly? If so, schedule a cleaning session for them and a class for the truckies on how to remove AC covered gloves.

MISCELLANEOUS COMPONENTS:

1- Air compressor: This unit should be scheduled for a complete service. Any associated air driers and lubricators should be cleaned at the same time. Examine all air lines, noting any problems.

2- Schedule a test session for all the thermometers on your plant. One easy way to calibrate them is to boil water, immerse the sensor end and adjust the thermometer to read 212 degrees, the boiling point of water at sea-level. Adjust the temperature for the altitude of your plant, i.e. 208 @ 1000ft. (check factuality of reading) Another way is to find a thermometer you know is accurate, such as an infrared hand-held unit, then set all the others to match it.

On the heat transfer oil system and the AC tanks you can check the operation of the high-temp shut-downs by immersing the sensors in the boiling water then slowly turning down the set-point controls until the unit shuts off. Record the setting and compare it with the boiling point of water at your altitude. Make the appropriate adjustments.

3- Portable AC plants usually rely on generators. Good advice would be to pamper this jewel since without it not much happens. Examine the radiator. Is it full of gunk? Schedule a thorough cleaning. Look at all the hoses and belts. Mark any that raise doubts. Schedule a complete service which includes testing and adjustment of the generator output. Do you have a stock of crucial spares such as control voltage fuses and possibly a regulator?

4- Examine the control van/room. Is it clean and neat or are there jumper wires sprouting from every panel and fuse box like the arms of Medusa? Do all the motor starters work as designed or do some have sticks jammed in the magnetic to hold it engaged while the operator relies on either the interlocks or the circuit breaker to start the motor? Don’t laugh, this happens far more often than anyone will admit. Schedule repairs as needed.

GENERAL MAINTENANCE:

All gearboxes and speed reducers should be examined for oil leaks and noted for repair if needed. It is a good idea to schedule each box for an oil change during the winter months. Collect properly marked samples from each box and give them to a reputable oil analysis company, they will be able to detect any abnormalities and perhaps avert a surprise breakdown at a later date.

A thorough greasing regimen should be completed prior to plant restart. For electric motors, follow the manufacturer’s recommendations. Each year numerous motors fail because uninformed oilers pump them full of grease like they would a troughing roller. Some motors vent excess grease internally, so once enough of the stuff is pumped in failure is bound to follow. Most motor manufacturers recommend a yearly greasing schedule consisting of one or maybe two pumps of the gun.

HOUSEKEEPING:

When getting ready for your annual DOT inspection it is good to remember that a clean plant will be inspected with a less critical eye than one which looks like it is operated and maintained by Larry, Curly and Moe of the Three Stooges fame. A clean and ‘squared away’ plant is also a safer environment to work in.