PILOT BURNER
   

STANLEY PILOT INSTALLED IN A STANLEY BURNER FOR A 20 HORSEPOWER CAR

CRUBAN PILOT INSTALLED IN A CRUBAN BURNER FOR A 20 HORSEPOWER CAR

Just as every gas stove, gas hot water heater, and gas-fired home heater has a pilot (or an electric ignition for the units made in recent years), the Stanley Motor Carriage requires a pilot for proper operation of the burner.  The pilot in a Stanley serves several purposes.  It provides an ignition source for the burner as it cycles on and off during the operation of the car.  It is positioned within the burner such that the heat of the pilot keeps the main burner vaporizer coil hot to facilitate vaporization of the burner fuel.  And a properly burning pilot will supply sufficient heat to the boiler when the burner is shut down so that the steam pressure is maintained for hours while the car sits idle.  Once fired up the pilot insures a Stanley is always ready to drive by simply getting in and opening the throttle.

Stanley pilots have always burned gasoline although many Stanley owners have substituted Coleman Stove Fuel or hexane in recent years as it burns cleaner with less fouling of the pilot vaporizer and nozzle.  The starting or "firing up" of a Stanley starts with lighting the pilot.  For this to occur the pilot must be manually heated with a torch to start the liquid fuel vaporization process.  Once the pilot is sufficiently hot, the pilot fuel valve is opened to admit fuel to the pilot as the torch is used to light the pilot.  Thus no Stanley ever had an ignition key.  Twenty-first century Stanley owners routinely use propane torches to light their pilots and are often heard to tell onlookers that "the ignition key for a Stanley is a blowtorch"

From the time one starts draining water off the boiler and heating the pilot until sufficient steam pressure is available in the boiler to drive the car can be as short as twenty minutes.  Stanley advertised this amount of time as required to drive a Stanley starting out with a cold boiler and if all goes well and one really pushes the process the 20-minute time is fairly accurate.  However most Stanley owners stretch this ritual out to as long as an hour by heating the boiler at a slower rate to lessen thermal shock and reduce boiler stresses. 

 

How the pilot Works

DRAWING OF A TYPICAL STANLEY PILOT SHOWING THE VAPORIZER LOOP, PILOT CASTING, AND PILOT NOZZLE.  tHE DRAWING REPRESENTS THE DESIGN OF AN EARLY CONDENSING CAR PILOT WHAT INCORPORATED ELECTRIC HEATING OF THE VAPORIZER.

A Stanley pilot, also referred to as a pilot burner by Stanley, is known as a vaporizing pilot or vaporizing burner.  Perhaps the closest cousin of the Stanley pilot burner are the Coleman Camp stoves with operate on similar principals.  The pilot burner functions similar to a Bunsen burner or a modern propane torch in burning gaseous fuel with the exception that the pilot burner operates from liquid fuel that must be vaporized into a gaseous state.  A Bunsen burner forces fuel that is already in a gaseous state through a very small orifice and into a vertical cylindrical chamber that forms the body of the Bunsen burner.  Air is admitted to the cylindrical chamber alongside the gas stream and the air and fuel mixture rises through the cylindrical chamber to a horizontal screen at the end of the chamber where combustion can occur on the upper surface of the screen.

The main part of the pilot is the pilot casting which is very close in size to the cardboard tube found inside a roll of bathroom tissue.  As shown in the diagram above, thin slots are machine-cut into the upper side of the pilot casting and extend through the wall thickness of the casting to the interior chamber.  The casting is hollow with a hole in it at the nozzle end and closed off at the opposite end.

Inserted into the opening in the end of the pilot casting is a mixing tube.  This tube runs the length of the pilot casting located along the central axis of the casting.  The mixing tube projects from the end of the pilot casting about a 1/4" and is flared slightly similar to a horn's bell.  This tube is open along the bottom or drilled with holes along its bottom surface.  Gas vapors in the mixing tube flow through the holes or slits in the bottom of the mixing tube and then up and through the slits of the pilot casting to burn on the top of the casting.

Above the pilot casting is a U-shaped tube which vaporizes the liquid fuel supplied to the pilot.  Designed to only work with gasoline or similar fuels that are easy to vaporize, the tube is generally 8" in length over the pilot casting.  The liquid fuel is admitted into one of the legs of the U-tube (the rear one in the drawing) and gaseous fuel discharged from the other leg is connected to the pilot nozzle.

In 1918 Stanley experimented with heating the pilot by applying power from the 6-volt battery and thus both legs of the pilot vaporizer were extended to permit the attachment of the heavy battery leads as shown in the drawing above.  Unfortunately this attempt at providing an electric starting capability on a Stanley was not successful due to battery construction of the period.  The 6-volt batteries of the era just couldn't stand the stresses of repeatedly delivering high currents for short periods.  Electric starting was also problematic because the generator on early cars was only rated at 20 amperes and turned out not to be sufficient to charge a battery properly unless the car was used for long duration trips at a decent speed (something the roads of the period generally did not permit).  The Stanley instructions suggested only using the electric start for 15 to 20 seconds and to drive the car 25 or 30 miles afterward to charge the battery.

The pilot nozzle is a hollow casting that includes a cone-shaped extension that enters the mixing tube mounted in the open end of the pilot casting.  At the point of the cone is a very small orifice (generally a #64 drill size for a Stanley pilot) for injecting gaseous fuel into the mixing tube.  The pilot nozzle includes a screw with a 0.036" diameter wire attached to the end of the screw and projecting through a hole in the end of the cone-shaped extension of the pilot nozzle casting.  The wire has a small flat filed into it (generally the flat decreases the wire's diameter to 0.029" at the flat) where it passes through the pilot nozzle's hole.  By rotating the screw the wire is turned in the pilot nozzle's hole and thus can clean any deposits out of the pilot nozzle's hole.

The pilot is lit by taking a torch and heating the pilot nozzle casting and the copper fuel feed tubing attached to the fuel side of the pilot vaporizer external to the burner.  When sufficiently hot (this generally requires two to three minutes of heating) the pilot fuel valve is opened to admit fuel to the pilot.  Upon contact with the preheated fuel supply tubing and the pilot nozzle the fuel vaporizes to a gas that flows out the small hole in the pilot nozzle and into the mixing tube.  As the fuel supply is under pressure the gaseous fuel exiting the pilot nozzle is injected at a decent velocity down the central axis of the mixing tube. 

As the gaseous fuel moves down the mixing tube it combines with air at at the proper air/fuel ratio for combustion to occur.  The mixture flows out the openings of the mixing tube and into the pilot nozzle casting.  The pressure differences of the mixture in the pilot casting chamber and the outside of the pilot casting allow the air/fuel mix to flow through the slots in the pilot casting where it is ignited and burned. 

The burning air/fuel mixture creates a continuous flow of air into the mixing tube with the gaseous fuel injected into the mixing tube by the pressure on the fuel system.  The burning fuel on the top side of the pilot casting heats the vaporization tube and allows the vaporization process to continue as fuel is fed to the pilot.  A properly adjusted and operating pilot should produce a blue flame similar to that pictured above right.

As a pilot burns carbon deposits may form on the wire and at the hole in the pilot nozzle.  This will reduce the gaseous fuel flow and cause the pilot to reduce its burning intensity.  This is quickly corrected by taking a screwdriver and giving the pilot nozzle screw a half turn and then reseating it several times in rapid succession.  It is imperative that the burner access port be closed anytime the pilot nozzle screw is moved as the screw will leak fuel which could be ignited by the pilot's flame and thus flash into flame in the presence of the operator.  In a like manner, due to the pressure on the pilot fuel system and the lengths of fuel tubing between the pilot valve and burner, the pilot may continue to burn for as much as 5 or 10 minutes.  Thus it is important to insure the pilot has been extinguished before performing any maintenance on either the pilot or the burner fuel systems.  Before blowing down a boiler the operator needs to insure the pilot is extinguished as the pilot can locally heat the bottom of the empty boiler and damage the flues.

A proper burning pilot should be blue with very little to no yellow present.  The appearance of yellow in the flame indicates that the air/fuel mixture is not proper for combustion.  The yellow condition may be corrected by changing the pressure carried on the pilot tank (generally the pressure should be somewhere between 20 and 30 PSIG).  If the flat on the wire is too small or too large an improper air/fuel mixture will result and cause the flame to show yellow.  If the mixing tube is blocked or otherwise damaged an improper air/fuel ratio or insufficient mixing will occur and the flame will show yellow color.

There were several manufactures that produced aftermarket pilots for Stanley steam cars.  Perhaps the best known was the Cruban pilot.  Manufactured by the Empire Burner Company in New York, the Cruban pilot for a Stanley burner included an extension to the mixing tube that Empire claimed would keep the pilot's flame from being extinguished when driving the car.  Empire also manufactured a complete burner assembly for Stanleys that includes a heavy, brick-sized pilot that was easily maintained.

 

 

 

 

 

LIT CRUBAN PILOT SHOWING THE PILOT'S FLAME IMPINGING ON THE VAPORIZER TUBE.  lOOKING BEHIND THE HORIZONTAL SECTION OF THE VAPORIZER TUBE REVEALS THE PILOT FLAME BURNING ON THE TOP OF THE PILOT CASTING.

 

 

 

 

 

 

 

 

 

 

PHOTOGRAPH OF THE VAPORIZER TUBE AND NOZZLE FOR A CRUBAN BURNER.

 

 

 

 

 

 

 

 

 

 

CLOSE-UP PHOTOGRAPH OF A CRUBAN BURNER CASTING SHOWING THE WORD "EMPIRE" DRILLED INTO THE CASTING.  THE VAPORIZED GAS PASSES THROUGH THE NUMEROUS HOLES AND BURNS.

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