Titan-Xpert
Active Member
Recently Titan customer support has received some inquires about a blue fuel stain, puddle appearing on the ground under the cowling, about 5 minutes after shut down. The fuel is dripping out of the sniffle valve. This one way check valve is normally installed on most forward facing induction systems, at the bottom rear of the plenum. The sniffle valve closes when the engine is in operation and is open any time it?s not running. Its purpose is to allow fuel from excessive priming to escape the plenum. If a large amount of fuel accumulated in the plenum, it could be inhaled as a large slug of liquid into a cylinder causing a hydraulic lock which can cause permanent damage to a piston or cylinder. If you over prime a fuel injected motor hot or cold it is normal to see this extra fuel leak out of the sniffle valve before starting the engine.
The source of the fuel stain appearing on the ramp 5 minutes after shut down was until recently unknown to us .We asked Mr. Don Rivera of Airflow Performance his opinion of the problem and this is his very knowledgeable reply. Quote
What is happening here is that the engine driven fuel pump is a diaphragm pump. The pump lever compresses a spring in the pump and the spring pushes on the pump diaphragm which sets the pressure and its displacement pushes the fuel out. So at shut down the pump has one stroke of fuel it will displace in the fuel injection system. The fuel leaks out the nozzles then runs down the intake pipes, into the plenum and out the manifold drain. This will happen with all types of fuel injection systems (Airflow, Bendix, Precision Silver Hawk) using a diaphragm engine driven fuel pump unless the system has a purge valve which will dump the fuel pressure at shut down thus eliminating the leakage out the nozzles.
The same thing will happen if the boost pump is energized and the engine is not running. The fuel pressure from the boost pump pushes on the diaphragm in the engine driven pump which compresses the spring in the engine driven pump. Then when the boost pump is turned off the engine driven pump will discharge one stroke of fuel into the system.
Don Rivera
The source of the fuel stain appearing on the ramp 5 minutes after shut down was until recently unknown to us .We asked Mr. Don Rivera of Airflow Performance his opinion of the problem and this is his very knowledgeable reply. Quote
What is happening here is that the engine driven fuel pump is a diaphragm pump. The pump lever compresses a spring in the pump and the spring pushes on the pump diaphragm which sets the pressure and its displacement pushes the fuel out. So at shut down the pump has one stroke of fuel it will displace in the fuel injection system. The fuel leaks out the nozzles then runs down the intake pipes, into the plenum and out the manifold drain. This will happen with all types of fuel injection systems (Airflow, Bendix, Precision Silver Hawk) using a diaphragm engine driven fuel pump unless the system has a purge valve which will dump the fuel pressure at shut down thus eliminating the leakage out the nozzles.
The same thing will happen if the boost pump is energized and the engine is not running. The fuel pressure from the boost pump pushes on the diaphragm in the engine driven pump which compresses the spring in the engine driven pump. Then when the boost pump is turned off the engine driven pump will discharge one stroke of fuel into the system.
Don Rivera