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NORA Oilheat Technicians Manual

Chapter 2 Heating Oil Figure 2-3: Relative size of micronic particles biologically active sludge. There is always some water dissolved in the fuel. This is why sludge can sometimes grow faster on filters and strainers than it can in the tank. The rate at which sludge grows depends on the temperature and the availability of moisture and nutrients. Filters may plug, even with new tanks and lines. The “seed” sludge particles can arrive with the fuel from a contaminated tank upstream in the distribution system. They can be drawn directly into the suction line before they have a chance to settle to the bottom of the tank. If the conditions are right, a filter can plug within weeks of installation, even with Chapter 2—Heating Oil and Its Properties 2-11 nozzle. There are two approaches to how a filter should react when it is full. Some filters allow oil to bypass the filter when the element is full; others are designed to stop the flow of oil when they are full. While the filters that will not allow bypass will cause a no heat call when they are full, they ensure that no particles reach the nozzle. With the bypass type filter, once the filter is full, it will allow the contaminants to flow down stream and plug the pump strainer and nozzle. This will take longer to happen, but when it does, it will require work on the burner. Many service managers are now advocating the installation of two filters on problem installations. They install a large standard cartridge bypass filter at the tank and a 10- micron no-bypass spin-on filter at the burner. Filters and sludge Filters may fail because they have become blanketed with biologically active slime or sludge. The resulting black or gray “ball of grease” is a tough service problem. This sludge is not material that has been sucked from the tank; it is alive and actually growing in the filter. When small particles of sludge in the oil tank are drawn into the oil line, the bacteria in these particles look for moist places to reproduce. If there is any water pocketed in the bottom of the filter canister or if there is water emulsified in the fuel, they can grow their biofilm. Contrary to popular belief, there does not have to be a layer of free water in order to support the growth of


NORA Oilheat Technicians Manual
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