Flow divider valve Fuel discharge orifice Screen Spin chamber Small slot Large slot Compressor discharge air Fuel inlet port Figure 2-66.  Duplex fuel nozzle.  Figure 2-67.  Flow divider.  pressure on the bellows also increases. At a predetermined  pressure, the bellows compresses, allowing the flow divider  valve to open. This action starts fuel flow to the secondary  manifold, which increases the fuel flow to the engine. This  fuel flows out of the secondary opening in the nozzles.  The fuel pressurizing valve is usually required on engines  incorporating duplex fuel nozzles to divide the flow into  primary and secondary manifolds. At the fuel flows required  for starting and altitude idling, all the fuel passes through the  primary line. As the fuel flow increases, the valve begins to  open the main line until at maximum flow the secondary line  is passing approximately 90 percent of the fuel. Fuel pressurizing valves usually trap fuel forward of the  manifold, giving a positive cutoff. This cutoff prevents  fuel from dribbling into the manifold and through the fuel  nozzles, limiting afterfires and carbonization of the fuel  nozzles. Carbonization occurs because combustion chamber  temperatures are lowered, and the fuel is not completely  burned. A flow divider performs essentially the same function as a  pressurizing valve. It is used, as the name implies, to divide  flow to the duplex fuel nozzles. It is not unusual for units  performing identical functions to have different nomenclature  between engine manufacturers.  The drain valves are units used for draining fuel from the  various components of the engine where accumulated fuel  is most likely to present operating problems. The possibility  of combustion chamber accumulation with the resultant fire  hazard is one problem. A residual problem is the deposit of  lead and/or gum, after evaporation, in such places as fuel  manifolds and fuel nozzles. In some instances, the fuel manifolds are drained by an  individual unit known as a drip or dump valve. This type  of valve may operate by pressure differential, or it may be  solenoid operated. The combustion chamber drain valve drains fuel that  accumulates in the combustion chamber after each shutdown  and fuel that may have accumulated during a false start. If the  Fuel Pressurizing and Dump Valves Combustion Drain Valves 2-47