Due to the increased use of all kind of additives in certain types of fuels and oils, these hydrocarbons can hold amounts of water in chemical emulsion. Although coalescers are highly (cost) effective in separating free and mechanically emulsified water, the presence of surfactants can reduce the efficiency of the separation.
In certain applications such as aviation refueling, where the presence of water is causing danger due to freezing at high altitude, water absorbing cartridges are used as a final treatment to assure that all water – including the chemically emulsified part – is removed from the fuel before it can cause danger. Since the water absorption capability is used as safety device the water absorbing cartridges are referred to as ‘monitors’. Since fuels can hold large amounts of water the treatment in the fuel with monitors is restricted to the final stage only. In the rest of the chain the fuel is normally treated with filter water separators.
Hydraulic oil usually contains high levels of surfactants to improve the performance of the oil. At the same time the intrusion of water is limited since hydraulic systems are closed loop systems. The only sources for water are tank breathing and seal failure. Due this the combination of high surfactant levels and low water content hydraulic oils are usually treated with water absorbing cartridges.
Water absorbing or monitor cartridges are a combination of fine filtration by means of a pleated assembly of fine-grade filter media. The pleated configuration is necessary to obtain the optimum area consistent with maximum dirt-holding capacity and efficiency. Following the almost total removal of solid contaminant by this first filtration stage the hydrocarbon/water emulsion then passes through the water absorbing media, containing a special hygroscopic material to remove free, mechanical and chemical emulsified water. The absorbed water is chemically bonded inside the water absorbing layers. Removed solids and absorbed water will increase the differential pressure over the cartridge. If the maximum recommended differential pressure is reached the cartridge(s) should be changed. The perforated metal reinforcement tube provides adequate rigidity to the whole assembly after it is finally sealed within the end caps using a high-quality oil-and-fuel-resistant adhesive. The structural strength of the cartridges is very high to prevent cartridge collapse if water or solids slugs appear in the system.
Monitor cartridges are available in a variety of sizes and filtration grades.