AIR VALVES
   

Pilot fuel tank (left) and burner fuel pressure tank (right) air valves

The air valves are located under the firewall floorboards on the front passenger side of the car.  The air valve assembly consists of a pair of valves on a common body and includes a standard tire valve (Schrader valve) for the connection of the air supply.  Air from a bicycle pump (or from a battery-powered electric air pump) is attached to the tire valve.  Then depending on which valve is opened, air is directed to either the pilot fuel tank or the burner fuel service tanks for pressurization.

The left valve in the photo (yellow valve in the piping diagram) admits air to the pilot fuel tank while the right air valve in the photo (red valve in the piping diagram) admits air to the burner fuel service tanks.

 

HOW THE AIR VALVES ARE USED

Both fuel systems on a Stanley Steamer are pressurized.  The pilot fuel system is the simplest of the two.  A tank located under the front seat holds the pilot fuel (originally white gasoline or camp stove fuel; today we use hexane because it burns very cleanly and doesn't tend to foul the pilot vaporizer with carbon).  In order to get fuel from the pilot fuel tank to the pilot burner under the boiler, the pilot tank is pressurized with air to 25 to 30 PSIG.  When the pilot fuel valve is opened (located near the pilot burner under the boiler at the left side of the car) fuel is pressure fed to the pilot burner from the pilot tank.

Filling the pilot tank requires that the cap for the pilot tank be loosened until the pressure in the tank is relieved.  The pressure of the pilot tank is displayed on a gauge located on the dashboard.  Once the pilot tank has been filled two-thirds full of pilot fuel (the tank can't be filled full as an air space is needed for pressurization) the pilot tank air valve (left valve in the photo above; yellow valve in the piping diagram) is used to repressurize the pilot tank to its proper pressure for operation.

The burner fuel system is more complex than the pilot fuel system.  During the operation of the car, over time, some of the air contained in the service tanks will diffuse into the kerosene much the same way carbon dioxide is diffused into carbonated sodas (it is the releasing of the carbon dioxide from the soda when it is poured in a glass that causes the bubbling action).  The air diffusing into the kerosene results in a decrease in the volume of air contained in the service tanks.  It is the air that provides the elastic properly within system and allows the pumps to actually build and maintain fuel pressure.  Reducing the volume of air in the tanks increases the tank volume available for the pumps to store fuel in.  Unfortunately the reduction in air space also diminishes the elasticity of the system such that each stroke of the fuel pump now has less air to push against resulting in the tank pressure building faster.

As the volume of air in the tank decreases it results in each stroke of the fuel pump building fuel pressure faster.  Thus the fuel gauge needle "bounces" such that each pump cycle increases the pressure while the burner operation is working to drop the system pressure.  When the bouncing motion of the fuel pressure gauge needle is observed it is an indication that air must be applied to the service tanks.  This is best accomplished the next time the car is fired up. 

To add air to the service tanks the burner fuel pressure is allowed to drop to 60 to 80 PSIG during the firing up of the car and then air is admitted to the service tanks until the pressure reaches 120 to 130 PSIG (assuming the air source is capable of supplying this pressure).  Basically the system pressure is being raised through the addition of air to the fuel pressure tanks instead of liquid fuel being added with the hand fuel pump.  The air source can then be removed and the burner fuel pressure allowed to drop again.  The burner fuel system pressure is then pumped up using the hand fuel pump.  If each stroke of the hand fuel pump handle only moves the fuel pressure needle the width of the needle or so then there is sufficient pressure in the system.  If the burner fuel pressure needle is moving a larger increment then additional air should be added to the system a second time.  If the air supply is only in the 90 PSIG range then air will probably need to be added several times before the system has the proper volume of air contained in the service tanks.

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