A Close Look At Oil Filtration

825-1Using supply line filters with oil burning equipment makes good sense. A major reason is the age of the oil tanks in the field. Over the years, sediment, or sludge, accumulates in the tanks. The sludge is produced from the molecules of water and heavy oil that form in suspension. As they get heavier, they eventually drop to the bottom of the tank. If sludge enters the oil distribution system, it can collect and plug the fuel unit, the nozzle line, or the nozzle. That’s why you need a filter.

A filter is a porous substance through which a liquid or gas is passed in order to remove, or strain out, solid particles and impurities. Filters can be made from a variety of materials, including wool felt, resin-coated paper, or stainless steel mesh. The majority of filters have a replaceable element, or core, that fits or drops into the holder of the assembly. Additionally, there are filters in use today which are spin-on types, similar to automobile oil filters. The stainless steel mesh filter is designed to be cleaned rather than replaced. All three types are connected to a stationary head assembly which is piped into the suction line. (See Figure 1.)

Selection of the Filter

825-2Your personal preference for a brand and the material construction is important. You must feel confident with the components you utilize in a preventive maintenance program.

To select the proper filter, you must know the following:

  1. Suction line size.
  2. Gallons per hour of flow rate through the filter.
  3. Type of fuel being used.

While all filters perform the same task, each manufacturer provides technical literature that categorizes each filter by flow rate (GPH) and by pressure drop (inches mercury/HG). You will also note that each filter will have a micron, or mesh rating. These ratings represent the amount of pressure drop or degree of filtration capability. A lower micron/mesh rating indicates a tighter filter construction and its ability to remove finer particles.

For a clear illustration of these details, refer to the information in Figure 2. Here is a cross-reference between the two terms and some familiar items for comparison.

Modern appliance designs are continuing toward smaller, more efficient units. The firing rates (GPH) are generally lower, requiring more protection for the smaller nozzle. To understand the micron rating, relative to nozzle protection, we will look at an example with a .65 GPH nozzle.

A nozzle has distributor slots that channel the oil flow. These slots are precisely machined for a specific pattern and flow rate. The .65 GPH nozzle slots have a width of six thousandths of an inch, or 150 microns.

In our example, you might conclude that any filter rated 150 microns (100 mesh) or less would be satisfactory. However, there is a condition that has been noted by filter manufacturers called “agglutination”. Because of this, and the need to protect the entire burner system, you are better off using a filter rated at 50 microns or less. Here’s why.

Agglutination occurs when small particles, much finer than 150 microns, begin to stick to one another and create a blockage in the nozzle. You could view this much like a number of small logs coming down a river. At the point where the river converges into a small waterfall, one of the logs jams. Consequently, more logs become entangled with the first one until a dam or restriction has accumulated. Similarly, when this occurs within the nozzle, it can produce conditions other than plugging the nozzle. The spray pattern can become erratic causing the burner to operate with incomplete combustion. This could cause unnecessary service calls and contribute to appliance sooting.

The burner has its own internal filtration system. In our example, the nozzle filter has a rating of 50 microns and the typical pump strainer 150 microns. To provide additional, vitally needed protection, selection of a filter that can screen less than 50 microns should be adequate.

Important Service Points to Remember

  1. The objective for installing a supply line filter is to remove impurities from the fuel oil BEFORE THEY REACH THE BURNER.
  2. Check the system for maximum flow rate requirements. A two-pipe system may move 22 GPH, while a one-pipe set-up may draw only the nozzle firing rate.
  3. Choose a micron/mesh rating that will adequately protect the nozzle slots and orifice.
  4. Use only good quality flare fittings in the oil supply system. NEVER USE COMPRESSION FITTINGS.
  5. Install the filter inside the heated dwelling if possible. Wax crystals or ice accumulation can block flow in cold weather.
  6. Replace the filter element regularly. Usually, this is done on an annual preventive maintenance basis.
  7. Be sure to dispose of used filters and waste oil in accordance with local codes.

Today, more than ever, it makes good sense to protect your oil burning equipment with proper filtration. You provide a valuable service for your customer, and strengthen our industry as well.