Water may be entrained in petroleum-based liquid fuel as free water suspended in droplet or particulate form, in emulsion, or in solution. Dissolved water in fuel is common and generally presents little difficulties for operation of particulate filters for the fuel, as long as the water remains uniformly distributed in the fuel. The capacity of fuel to hold water in solution changes as a result of temperature changes, and in many cases, the finely-divided water particles will coalesce into larger particles in an undissolved state, which settle out because their density is greater than the fuel. Particulate fuel filters, frequently being formed from paper, degrade as the pores of the paper become clogged with the undissolved water, which can increase the pressure drop across the filter.
It is therefore important to remove the undissolved water particles suspended in the fuel before the fuel passes through any filter medium for removing solid particulate contaminants. The removal of water from the fuel system also prevents filter and fuel line freeze up.
It is also important that a water separator for a fuel supply system for a diesel engine pass solid particles of a larger size than the droplets of the water to be removed. Under some low temperature conditions when the suspended droplets of water are removed from the fuel by freezing, wax components of the diesel fuel coagulate and may form wax particles. It is important that the water separator pass such particles to prevent clogging of the separator and consequently, engine stalling.
One early type of water separator shown in U.S. Pat. No. 3,785,970, where a nylon sock had its open end sealed around the inlet passage to the separator so that the flow of fuel through the sock maintain the sock in an inflated condition. Using a nylon sock, there is an uniform minimal pressure drop across the entire porous surface of the sock. The pores of the sock are expandable to reach a state of equilibrium in which pores are of a size to create the pressure drop required to accommodate the established flow rate of fuel. The expandability of the pores also permits the passage of filterable particulate matter suspended in the fuel so that the water separator is not clogged by large wax particles of fuel under low-temperature operating conditions.
While the water separator shown in the '970 patent has certain satisfactory qualities, the water separator has certain limitations as to structure and application, and was not particularly suited for a spin-on capability with a replaceable transparent collection bowl, to allow the separator to be easily attached to and detached from a manifold head, and to visually inspect the level of water in the separator element. Such spin-on types of elements with collection bowls have received wide-spread acceptance in the marketplace and consumers are generally comfortable and knowledgeable about their use and application.
It is also believed there is a constant demand in the industry for new and improved water separators, particularly water separators which incorporate few components, are easy to assemble, and which provide efficient separation of water from a water/fuel mixture.