Preventing Water From Entering The Fuel System

Water and oil do not mix. Furthermore, water can create nuisance service problems in the oil supply system such as:

  • Causing rust to form in the tank and lead to fuel pump damage.
  • Freezing and blocking the supply line in certain outside tank installations.
  • Providing an environment for bacterial growth and sludge formation.
  • Contributing to filter blockage, erratic burner operation, nozzle clogging and safety lock-out.

How can these problems be prevented or at least substantially reduced? First of all, it is vital to understand what the root causes are and then take appropriate measures to eliminate them.

Underground Tanks

With underground tanks, leakage can be traced to several root causes.

  1. 835-1The fill box is usually flush with the ground and requires a suitable gasket around the plug to prevent water from seeping in after a rainstorm. It must be tight and in good condition in order to provide a dependable seal. (See Figure 1.)
  2. The vent pipe must have a shielded cap to protect from rain and should be located above the “snow line” and away from gutter down spouts.
  3. All pipe fittings must be tightened securely and have the threads sealed with a resilient compound that can endure the environmental variables in temperature. Any loose or poorly sealed joints can permit ground water to infiltrate the storage tank.
  4. Sometimes, the tank can develop a leak and ground water can seep in when the oil level is low. Check for water contamination using a dipstick and a water-finding-paste. It changes color when water is present. A leaking tank must be replaced in accordance with local and other codes.
  5. Another possible, but rare contributor, could be due to storage and maintenance practices in the distribution system. Large bulk storage tanks must be checked for condensation accumulation and bled periodically. If this is not done conscientiously, then it is possible for water to be drawn out with the oil when the stocks are extremely low or when the bulk storage is filled and the water is forced into temporary suspension. Fortunately, our industry has implemented effective preventive maintenance measures and this has been virtually eliminated. However, if water and sludge are found in a tank that does not have a leak, then it must be thoroughly pumped out, cleaned and treated with a chemical additive that disperses water, sludge and neutralizes bacterial growth.

Above Ground Tanks

  1. Again, the fill pipe must be properly capped and sealed to prevent rain from penetrating.
  2. The vent pipe must also be capped with a shielded vent cap and located away from roof edges where water could splash onto the tank and up into the vent pipe.
  3. Tanks located outside can generate water through the process of condensation. For example, a partially-filled tank is exposed to temperature variations. During the day, the oil may be heated by the sun shining upon the tank surface. The oil expands pushing air from the tank. The temperature gradually falls during the evening and the oil volume is reduced, pulling in moisture-laden air that condenses on the cool walls and accumulates in the bottom of the tank. This process is repeated, perhaps daily until the water level enters the oil supply piping and precipitates a burner safety lock-out due to the factors mentioned in the introduction.
  4. Several service practices can successfully alleviate the problem outlined in the previous paragraph.
    1. Paint the tank silver which reflects the sun’s rays and reduces the thermal expansion problem. Locate it in a shaded area if possible.
    2. Install the tank so that the fill pipe end is pitched downward. This makes the water pool at that end where it can be readily checked and pumped from the system.
    3. Some installers solder a 3″L x 1/2″ O.D. copper tube in the tank valve to ensure that the oil is always drawn at least 3″ above the tank bottom.
    4. Older tanks had ports located so that the pitched end could be fitted with a drain valve. The opposite end had a port approximately 3″ above the bottom for the supply line connection. This was a serviceable design but is hard to find today.
    5. Another method to ensure that oil is drawn above the water/sludge level is accessed from the top. 3/8″ O.D. copper tubing is installed in one side of a duplex bushing and positioned 3″ from the bottom of the tank. It is held in place by a 3/8″NPT x 3/8″ compression adapter.
    6. Keep the tank filled during the warm weather, since the air space at the top will be reduced and condensation should be minimized.

Water should be kept from remaining in the fuel tank. It is good practice for the tank to be checked with water-finding-paste, preferably before each fill-up, but at least annually. Any accumulation should be pumped out. If the water has gotten into the supply tubing, it should be pressure-cleaned with a hand pump or CO₂ charge. The filter, pump and nozzle tubing should be thoroughly cleaned and the nozzle replaced. Tests should be run to make sure that the fuel pump has not been damaged. A suitable chemical additive can be used to further disperse moisture, sludge and act as a bactericide. Following these outlined procedures can assist you in reducing nuisance service problems due to water contamination.