Commonly Asked Questions
Theory of Operation


4&5 Series
7 Series


4&5 Series
7 Series

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When should I change the AquaShield filter, or how long will an AquaShield filter last?
  • FSI International recommends that a customer change filters at intervals recommended by the equipment manufacturer. However, poor quality of fuel may signify the need to change filters more often. If a customer has 5% water in any type system, he will experience very short filter life. A customer using AquaShield filters as primary and secondary filters, and receiving fuel from a dispenser outfitted with an AquaShield filter, will experience a longer life from his/her on board filters because the dispenser will be delivering clean, dry fuel to the tank of the equipment or vehicle.
Will the AquaShield filter remove additives from fuels or lubricating systems?
  • No. The AquaShield filter does not remove any additives from the product being filtered.
Will the use of an AquaShield filter void my warranty?
  • No. A federal trade act called the Magnusson Moss Act (USA) states that a manufacturer cannot require you to use a specific filter unless that filter is offered to the end user free of charge. A copy of this federal trade act is available from FSI International.
Will the AquaShield filter freeze in subfreezing conditions?
  • No! FSI International has designed its filters to reduce the fuel flow when pleats swell. The operator will be aware of loss of power, alerting the operator to change fuel filters. Note: AquaShield filters will not allow enough water contamination to enter the injector system to cause any water damage even if the filter is saturated.
Is there any difference in the filter media in an AquaShield filter spin-on fuel (Model "F") or hydraulic filter (Model "H")?
  • No. Both filters have AquaShield's special water removing media, as well as the standard 10 micron nominal particulate protection. The difference is in the tap size (see AquaShield Specification Chart); the AS405H10 and AS409H10 come only with the inner gasket.
Why is a dispenser pump filter important (AquaShield Model AS405D10)?
  • This filter removes contamination such as water, dirt and bacteria from the fuel as it is pumped from the fuel storage tank. This pre-cleaning of fuel will help extend the service life of the primary and secondary filters installed on the engine.
If I cut an AquaShield filter open after an "in use" period, will I see water inside the filter can?
  • This really depends on how long the filter has been sitting before you cut it open. It is possible that some water could settle out of the fuel into the bottom of the filter can if the fuel is very contaminated and the equipment has been sitting for some time. Normally, you would not see free water. You may see gelled water on the outside of the pleats if the fuel flow velocity has been slow. If the flow velocity is high, then the entrapped water may be harder to observe as it will tend to be buried deeper into the pleated media.
Why is water contamination in diesel fuel systems so harmful?
  • A diesel fuel injection system is made of precision components with extremely close tolerances that rely completely on the diesel fuel for lubrication. Water entering the fuel injection system causes all manner of problems, both to the fuel system as well as to the engine itself. Scored pump surfaces, destruction of the injector nozzle, premature valve wear and cracked cylinder liners: these are just a few of the problems that result when water is present. Water combined with sulphur (that can be as high as 0.5% in today's fuel) form a corrosive acid that not only cause wear to the fuel injection system, but also find their way into the lube oil resulting in premature bearing wear.
How does water contamination occur in diesel fuel?
  • Water occurs in diesel fuel when warm moist air condenses as temperatures change. An example is a truck on the road. As the fuel tank empties the incoming hot return line, fuel flow cools down and condensation occurs. Of course, contamination can occur from the introduction of water directly into the fluid. Faulty storage tanks, poor housekeeping procedures, or possible sabotage might all contribute to the contamination problem.
What contaminants does diesel fuel frequently contain?
  • Dirt
  • Water
  • Bacteria
How does water enter a storage or a delivery system?
  • Inconsistency in diesel fuel handling contributes to water in fuel. Water can enter underground tanks through deteriorated tank walls or down the filler tubes. Changes in atmosphere temperature can cause condensation to form tank walls and accumulate in the bottom of the tank. Condensation also occurs when warm fuel is returned to the fuel tank.
In what application can the AquaShield portable filter buggy (Model AS-P100) be used?
  • To filter reservoirs of various hydrocarbon products such as hydraulic fluids, turbine oil, quench oils, cutting oils, gear oils, diesel fuels, solvents and even coolants such as non-water-based antifreeze. The portable buggy can also be used to transfer new product from a drum to a reservoir, or vice versa.