Coil Service

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Scale Removal

Running an acid solution through the coil is a solution for scale buildup developed in the early days of steam cleaning. Since water in a steam cleaner is heated to 325 degrees Fahrenheit and Inflatable water slide Costco beyond, impurities precipitate out faster, and scale can be more of a problem than in a hot water high pressure cleaner. This process can be time consuming and expensive and involves potentially dangerous chemicals. If done improperly, acidizing can literally eat up a coil.

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Under normal operating conditions scale can be removed periodically by short term circulation of acid, sometimes called “proofing.” This won’t remove major scale buildup but will remove scale buildup from cleaning chemicals. Scale can be a serious problem in a hot water machine in hard water areas, and the choice may be between scale removal or coil replacement.

 

Important Things To Know About Descaling

If scaling has progressed to the point where scale removal is necessary, there are several important points to remember.

Descaling should be done with great care and attention paid to all precautions. After all, even if it’s diluted, it’s still acid.

If possible, a descaling pump rather than the machine’s water pump should be used to circulate water through the coil. Many older steam cleaners used diaphragm pumps because they are good acidizing pumps with little susceptibility to acid damage. If the water pump is used, the parts that come into contact with the acid solution should be checked for damage and replaced if necessary.

The proper kind of acid should be used. Generally this is a self-inhibited acid, or one that does not attack the metal but confines its activity to the deposits inside the coil. A seven percent hydrofluoric acid solution is considered “heavy duty.” Acid purchased from a swimming pool supply house is not inhibited and should not be used. Stainless steel coils need special treatment since even inhibited hydrochloric or hydrofluoric acid attacks a stainless surface.

The acid should be neutralized with a good alkaline, and never just dumped down the drain. One should dress for the occasion, wearing protective clothing and goggles to keep acid from contact with skin and eyes. Always descale in a well-ventilated area. Descaling requires the use of strong acid and alkaline chemicals. Protect eyes and exposed skin areas from splash and splatter. Wear eye protection. If chemicals come in contact with skin or eyes, thoroughly flush with water and see a doctor immediately.

Proofing a coil by running a gallon of acid solution through the coil simply widens the narrowest spots in the scale deposit but does little to solve the insulation problem. 

Sooting And Other Problems

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Sooting:

Carbon deposits on the coil from smokey combustion can also reduce heat exchange efficiency. The soot acts as an insulator, making it harder to heat water in the coil. A one eighth inch soot deposit can seriously impair heat exchange efficiency.

Smoke needn’t be visible for sooting to result. Flue gasses that do not include visible smoke can cause heavy sooting. Soot can be removed by washing the outside of the coil. This is likely to require removal of the coil wrapper if not the coil itself and can be a very dirty job.

Heavier carbon deposits which build up from flame impingement on metal or other combustion problems may require special treatment. Heavy sooting is generally the result of a burner adjustment problem. The type of fuel used can contribute to sooting problems as well. The heavier the fuel oil, the more likely heavy sooting will occur. Kerosene, on the other hand, has fewer carbon molecules than fuel oil and will generally produce fairly clean combustion.

Corrosion

Corrosion and rust can also damage the coil. Condensation in the ceramic insulation blanket can cause external corrosion which will eventually lead to coil failure. Condensation occurs when hot air containing water vapor comes in contact with the colder coil surface. When this happens the vapor turns into water droplets adhering to the colder coil surface. Combustion byproducts, including sulfur from diesel fuel, may combine with the condensed water, forming sulfuric acid which speeds corrosion. An air-cooled boiler assembly helps reduce and control the condensation problem. Some equipment uses stainless steel coil tubing to resist corrosion.

Water Torgue And Water Hammer

As water flows through the coil, it follows a natural tendency to move in a straight line rather than through the curved path through the coil. This tendency to unwind the coil is often referred to as the water torque or effect because it becomes more pronounced as pulsation increases. The resulting stress can cause welds or weak points in a coil to fall.

The water hammer effect is the result of stopping and starting water flow rapidly in succession. This effect can be approximated by severe pump pulsation or cavitation. Pipes rattle in older homes when the faucet is shut off is another example of the water hammer effect.

Coil Service

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Removing the coil from a hot water cleaner is a relatively simple procedure. However, the coil is heavy and likely to be covered with carbon deposits. Care should be taken in handling the coil, and coil removal should be done in an area that can be readily washed. Coil removal can be very dirty and carbon deposits or soot can spread quickly to a large area of the shop if their containment is not carefully planned. The process may be complicated by ill thought-out designs and manufacturing techniques.

Procedures for removing and replacing the pancake type coils used in most horizontal and vertical cleaners manufactured in the United States will be covered first. Coils in these equipment types are generally insulated with a ceramic fiber blanket. In both horizontal and vertical types the coil is contained in a welded steel can or wrapper with at least one end cap held on by sheet metal screws. This coil wrapper holds the insulating material against the outside of the coil.

In all cases the inlet and discharge hoses must first be disconnected from the coil. The discharge and inlet lines are usually connected to hex couplings mounted on six-inch long nipples which are connected to the threaded coil pipe. Both connections are high pressure connections. In some cases one nipple, usually the inlet, may be shorter than the other. In some instances the protruding outlet connection may not be a nipple but actually part of the coil itself. In this case the coil wrapper or can will probably have a slot cut into the can to facilitate removal once the end cap is removed. If there is no slot, the can or wrapper may have to be cut off the coil. (This is fairly rare.)

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On vertical designs an elbow and vertically running length of pipe may be attached to the discharge nipple. This allows for the mounting of a strap-on thermostat. A high temp limit switch, a quick connect, a pressure relief valve or an injector may also be connected at the discharge point. Generally these control devices do not have to be disconnected for coil removal. Remove the nipples from the coil by unscrewing them. In cleaners with horizontal boilers, the burner assembly must be removed to access the coil.

Two fuel lines connect the fuel tank to the burner assembly. These must be prevented from leaking or siphoning when the burner assembly is removed. Siphoning can be prevented most easily and effectively by fabricating a coupling with a hose barn on each end. Remove the inlet and return lines from the fuel tank and connect them with this coupling. The lines may then be moved out of the way until service is finished. Alternative methods include replacing the hose barbs or connectors on the fuel tank with solid plugs or (for a short time only) using locking pliers such as vise grips to simply clamp the lines shut.

Service Hint: Mark the inlet line to the fuel pump as some manufacturers will use longer internal connections to prevent pick up of water or debris from the bottom of the fuel tank. (In most United States produced cleaners the fuel tank connections are on the bottom of the tank and longer internal connection lifts the fuel intake up from the bottom of the fuel tank.)To dismount the burner assembly, unscrew the three 9/16 inch nuts mounting the burner to the studs welded on the can. These nuts hold the burner mounting flange to the coil wrapper end plate. Take care that the burner does not fall off when the nuts are removed.

Note: The nuts are located with one on top and one on each side. If all three are loosened and the two outside ones are removed first, the remaining center nut will support the weight of the burner and ease handling.

The nuts may be screwed back on the studs to prevent their being misplaced. Set the burner aside, preferably away from the area where the coil is being removed. With the burner removed the end plate can be removed from the can. Remove the three to six sheet metal screws holding the end plate on. The end plate on the burner end will generally fit tightly inside the can. Take a screwdriver and insert it into the crack between the end cap and the can and gradually spread the can and end cap apart so that the end cap will come out evenly. If the cap is crooked, it will bind and make removal more difficult.

Pull the loosened end cap off the can. After the cap is removed, pull the coil out. Exercise care; the coil will weight 75 pounds or more. It is recommended that two people work together to remove the coil. The coil will probably be covered with heavy carbon deposits or soot.

Note: On a few models produced by American manufacturers, the rear coil support leg may be welded to the wrapper. Whitco cleaners generally have this feature. To remove the coil this tack weld must be broken. A hammer and chisel, cutting torch, or grinder may be used to defeat the spot or tack weld.

Vertical Cleaners

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On a vertical boiler the procedure is similar except the sheet metal screws holding the stack end cap on the can are removed and the stack end cap pried evenly out of the can. On some designs the end cap may be fitted over rater than inside the can. Use the screwdriver to gently and evenly drive the cap up until it slips off the can.

The burner does not have to be dismounted for coil removal on vertical cleaners. It is generally best to apply some kind of mechanical advantage when removing the coil from the vertical can. The coil must be lifted straight up out of the can. A hoist may be set up in the shop for such jobs or the coil may be chained to one of the fork lift’s forks and pulled straight up out of the can. When the coil is removed, it should be pressure-washed to remove soot or carbon deposits from the coil. Since the coil has already been removed from the cleaner there is no excuse for not doing a thorough cleaning job.

Service Hint: Be sure to clean the coil pipe from all directions and angles. Try to force water into all the gaps between the coil pipe. Clean the coil until no more “black water” or sooty runoff is present.

A good alkaline cleaning chemical and hot water are generally adequate. Special chemicals or compounds usually are not necessary. The coil should be cleaned in a well drained area. In some instances the coil may have been removed specially for cleaning. This process is called desooting. Effective desooting requires coil removal.

Service Hint: The soot or carbon deposits washed off of the coil will not mix well with water but instead float on top of the runoff water. The soot goes everywhere the washwater runoff goes, creating a spreading, black mess. When the washwater evaporates, the soot will remain. These carbon deposits can be tracked everywhere. The almost unbelievable ability of this black mess to spread is an important factor to consider in deciding where the coil should be cleaned.

Inspect And Replace The Coil

Once the coil is clean, inspect it for damage or corrosion. Look inside the coil bucket carefully and inspect the coil pancakes if you are trying to locate the spot where a coil has burst. When the coil is removed, the ceramic fiber insulating blanket will probably come out with the coil but generally will not be in good condition. In almost all cases the insulating blanket will be ruined and need replacement. Make sure there is plenty of insulating material on hand to replace the insulation before you pull a coil.

To replace the insulating blanket, new insulating material will have to be cut to fit. Clean and sweep the floor before cutting insulating material. Prepare the insulation and roll out approximately four feet on the cleaned area of the floor to begin cutting patterns. Take the end cap and place it on the blanket with the exterior side facing upward as close to the corner of the material as possible in order to conserve material.

Cut out a piece of material using the end cap as a pattern. Applying pressure of no more than the weight of your body, press the end cap into the material. This will make a deep impression that will allow for easy cutting. It is unnecessary to mark the material with a pencil. It is acceptable if the material is cut just a little large so that it will fit tightly into the cap.

Use a utility knife to cut the insulating material. Several passes or cuts may be necessary to cut through the 1” thick insulating blanket. Do not try to cut the blanket in a single pass as it is likely to tear. The end cap should be used to make a second impression and the insulation for the burner end of the coil can be cut. Once this piece is cut, it may be inserted in the burner cap to allow tracing or marking the hole for the burner through the hole in the end cap. The insulating material should be inserted in the end cap so the exterior side is facing into the end cap. Cut the hole for the burner assembly slightly smaller than the marked circle. Lay these two pieces aside for later.

Unroll several more feet of fiber blanket in the same clean area. Place the coil on the blanket horizontally and hold the end of the blanket on the coil. Roll the coil forward until the loose end of the blanket meets the remainder of the blanket so that the coil is completely covered. Mark where the blanket meets itself. Cut the blanket at the mark. Wrap the coil completely with the cut length of blanket, and secure it tightly at three different points with glass tape or other strong packing tape. Secure the blanket with one piece of tape about 2” to 3” from each end and one at the center. If the blanket is not held on to the coil tightly you will experience difficulties reinserting the insulated coil in the can. The coil will go into the can, but the loose blanket will hang up on the edges of the can and the coil will be pushed out of the blanket.

Place one end of the blanket even with one end of the coil and cut any excess insulating material from the other end of the blanket. Once the blanket is secured with tape and trimmed to the proper length, look for the coil inlet and outlet. Mark the blanket and cut holes for the nipples. These holes must be as small as practicable to prevent any combustion air leaks. A small “X” may be cut for each nipple instead of a round hole. The insulation may be installed in the far end of the can. Again orient the nipple connections on the wrapped coil to the holes in the can and slide the insulated coil into the can, pushing the insulation carefully into the can to keep it from bunching up or sliding back on the coil. The more tightly the insulation is secured to the coil, the less slippage and bunching will occur. Additional bands of tape on the outside of the coil insulation will help reduce drag.

Place the end cap insulation with the burner hole cut in it into the end cap. Install the burner and end cap on the can. Make sure the burner flange studs and sheet metal screw holes are properly oriented and tap the end cap on the can until the sheet metal screw holes line up. Replace the sheet metal screws and tighten them. Take care that you do not strip the screws.

Using a utility or X-acto knife, reach down through the stack to evenly cut out a hole in the insulation for the exhaust using the flue opening itself for a template. In addition to the blanket wrapped around the coil, a piece of insulation will need to be cut out for the flue or stack assembly as well in a vertical cleaner. Re-install the burner assembly onto the end cap using the proper burner gasket for a tight air seal. Tighten the retaining nuts.

Servicing Air-Cooled Coils

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Most European-designed cleaners have air-cooled rather than insulated boiler assemblies. Since there is no insulation, removing and replacing a coil in boilers of this type is generally easier and somewhat cleaner than in insulated boiler designs.

The air-cooled boiler has two cans or wrappers, often stainless steel, set inside each other. The blower forces air between these two cans and up to the burner mounted at the top of the boiler. When air flow reaches the top of the assembly, it is trapped and can only escape downward into the combustion chamber. Remove the two ignition wires from the electrodes and unhook the fuel line from the boiler cap. Do not remove or disassemble the cap at this time.

Service Hint: Some machines will have the fuel solenoid valve mounted directly on the fuel plumbing on top of the boiler. If so, removal of the entire assembly is unnecessary. Simply remove the solenoid coil from the valve housing, leaving all electrical wires in place on the coil. The coil and attached wires can simply be moved out of the way during service.

The air-cooled coil will have its inlet and outlet fittings at the bottom of the coil. Generally the inlet line will be a hose from the pump delivering cold water to the coil and the outlet lines will be metal tubing for better heat resistance. Once the fittings on the tubing are disconnected, there is usually a retaining nut and spacer or washer securing the coil to the can or machine.

Remove And Replace The Boiler Assembly

Three or more bolts will hold the boiler assembly to the cleaner’s frame. Remove these bolts and lift the entire boiler assembly off the cleaner. By removing the entire assembly at once, any soot deposits which have collected in the boiler will be contained and not spread all over the rest of the cleaner or the service area. Once the boiler assembly has been removed from the cleaner, place it in an area which can easily be cleaned.

To remove the coil from the inner and outer coil wrappers, first remove the exposed acorn nuts on top of the boiler. These secure the end cap onto the boiler assembly outer wrapper. Tap the outer end cap off of the can or wrapper. Remove any spacers and the second set of retaining nuts and washers that secure the inner end cap to the inner can or wrapper. Then remove the inner cap and set both caps aside. It is likely that both caps will need to be cleaned. The coil will now simply slide upward out of the inner wrapper.

Note: The inner and outer wrappers are lightweight sheet metal and will not completely retain their shape once the coil is removed. They are easily bent or creased so care must be taken in their removal. Make sure spacers, washers and o-rings are replaced in the proper positions.

With the coil removed, clean all carbon deposits from the coil, wrappers and caps. Use the same procedures and care as prescribed for cleaning United States-produced coil assemblies. Replace the coil carefully inside the inner wrapper, making sure the inlet and outlet are properly oriented. The inside coil carefully inside the inner wrapper, making sure the inlet and outlet are properly oriented. The inside coil leg is usually the inlet. Replace the inner cap. Replace the outer wrapper and cap. Reset and bolt down the boiler assembly to the frame and reconnect the inlet, outlet and fuel lines and the connections to the electrodes.

Ghibli cleaners have a horizontal coil surrounded by a water jacket which both preheats the water and cools the boiler assembly. To remove the coil from this type of cleaner, disconnect the inlet and outlet lines located on the end opposite the burner assembly. Remove the end cap from the end away from the burner. You may now simply slide the coil out. When re-installing, a new water jacket gasket may be required to prevent water leaks.

 

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