|STACK BLOWER VALVE|
the stack blower valve located under the dash in easy reach of the driver's left hand
There are two additions made to a Stanley Motor Carriage by present-day Stanley owners that are considered acceptable and generally are not considered to degrade the value of the car. While both additions were never provided on cars leaving the factory, the addition of these modifications provides the invaluable benefit of making the car safer to own and to operate. The first of these additions is the conversion of the foot brake from a mechanical design of asbestos lined bands and brake shoes to a hydraulic system that includes the use of modern brake shoes and materials. The second enhancement is the addition of a steam stack blower for assisting in the rapid extinguishing of a fire resulting from a burner backfire.
The stack blower has its origins with steam traction engines and locomotives. For traction engines and locomotives the stack blower is a necessity as it is used to induce draft for the boiler when the engine is not working. Both traction engines and locomotives incorporate boilers that do not have good drafts if the steam engine is not working. The stack blower provides a means to induce draft in steam traction engines and locomotives.
The Stanley’s vertical tube boiler design coupled with a liquid fuel burner does not require a stack blower to induce draft through the burner and boiler. However, the Stanley burner design, when not functioning properly, can backfire and combustion of the fuel can occur in the mixing tubes. This can be damaging to the tubes and the burner grate if allowed to continue too long. Many Stanley owners have added a stack blower to their cars as a means to induce a strong draft through the burner and boiler flues for the purpose of extinguishing the flames during a burner backfire.
PROPER USE OF THE STACK BLOWER
Examination of a steam traction engine or locomotive boiler reveals how air and combustion gasses flow through the boiler. Air is drawn in beneath the firebox grate where it passes up though the coal to feed the combustion process. The air, now in the form of hot combustion gas, travels through the flue tubes of the boiler were the heat of the gas is transferred to the boiler water. Upon exiting the boiler flues the combustion gasses accumulate in the smoke box.
Steam exhaust from the steam engine is directed to a nozzle in the smokebox that points up towards the smokestack. As the blasts of steam exit the steam engine’s cylinders the rush of steam up the smokestack pulls the accumulated combustion gasses in the smokebox with it. This creates a small vacuum in the smokebox that draws air through the boiler flues. This action subsequently draws air from the firebox above the bed of coal. The combustion gasses removed from the firebox are replaced with air from under the grate covered with coal.
When the steam engine is not running there is no steam exhaust to assist in drawing fresh air into the fire or to pull the hot combustion gasses through the boiler flues. A stack blower is nothing more than another nozzle in the smokebox that directs a flow of steam up the smokestack. Thus the stack blower provides a means to induce a supply of fresh air to the bed of coal in the firebox and to draw the hot combustion gasses of the fire through the boiler.
The Stanley boiler and burner design provides a natural flow of air through the boiler. As the fuel is injected into the mixing tubes it draws the air needed for combustion with it. This air/fuel mixture is discharged under the grate where it passes though the grate’s openings to burn on the topside of the grate. The combustion gasses then travel up through the boiler flues to the smokebox where they are directed down and under the car for discharge.
Stanley non-condensing cars were designed with an exhaust duct along the left side of the car. This duct is connected to the boiler smokebox to conduct the combustion gasses to the rear of the car. Inside the duct is the boiler feed water heater. The exhaust steam leaving the feed water heater is discharged into the duct where it helps draw combustion products and gasses through the exhaust duct, from the smokebox above the boiler, through the boiler, and to draw in fresh air to the burner in much the same manner as occurs with a steam traction engine or locomotive. With this arrangement simply driving the car insured a high quantity of air is moved through the burner mixing tubes and helps to prevent burner backfiring.
When Stanley developed the condensing cars, due to space limitations, the use of an exhaust duct was discontinued. Additionally the steam exhaust from the engine was now directed to the condenser so it was no longer available to help create a draft on the exhaust duct that had been present on non-condensing cars. Instead, condenser car combustion gasses were discharged from a duct located at the front bottom of the water tank. This arrangement had the negative effect of not providing the level of draft on the burner and boiler that had been available with non-condensing cars. Thus the probability of a burner backfire was increased on condensing cars over what had been experienced for non-condensing cars.
A burner mixing tube fire, or burner backfire as it is often referred to, generally results if the vaporizer coil is allowed to cool too much and fuel is supplied to the burner. If the burner fuel valve is opened (or the steam automatic opens fuel flow due to a drop in steam pressure) when the vaporizer coil is too cool to permit complete vaporization, liquid fuel will be sprayed into the mixing tubes along with what fuel might have been vaporized. With sufficient liquid fuel accumulation in the mixing tubes ignition can occur (the pilot makes an excellent ignition source) and a burner backfire results. The heat of this fire will damage and even melt the mixing tubes and often can crack the cast grate of the burner if the fire burns long or hot enough. By activating the stack blower the airflow through the mixing tubes can be increased to the point that the flow of air is sufficient to draw the fire out of the mixing tubes and extinguish it in the boiler flues. Continued airflow through the mixing tubes cools the mixing tubes and removes the ignition source (heated walls of the mixing tubes) so that a fire does not reignite.
Stanley did not consider the addition of a stack blower warranted and thus no Stanley model was ever produced with a stack blower. When Stanley Motor Carriages became automotive collector keepsakes the backfiring potential of condensing cars became an increased concern. Replacements parts were not readily available and maintaining a Stanley in original condition pays benefits in the value generally placed on the car. The addition of stack blowers became a common practice on many restored Stanley cars as a way to limit backfiring damage to the burner and fire damage to the car’s paint and structure. Having a stack blower present may be considered by some to degrade the worth of a Stanley but considering the alternative of a permanently damaged or destroyed car, the addition is generally accepted and even desirable. The acceptance of adding a stack blower on condensing cars has spilled over to then now being found on some non-condensing cars as well.
The addition of a stack blower is relatively easy to implement on a Stanley considering that replicated Stanley valves are available. The addition of a stack blower involves mounting a Stanley valve through the firewall (as shown in the picture at the top of the page) of the car in such a way to make it appear like the valve was original from the factory. The valve is plumbed to a source of saturated steam from the top of the boiler usually by tapping into a steam line used for the steam automatic or water siphon. In the exhaust duct that leads from the smokebox and down alongside the boiler a short length of copper tubing is installed at the center of the duct (see the photograph above right). This length of tubing is connected to the stack blower valve. When the valve is opened the steam blast exiting the stack blower tube in the exhaust duct serves to move the gasses of the duct quickly to the duct’s discharge end and results in increased air being drawn into the burner mixing tubes. This rapid increase in airflow in the exhaust duct draws air through the boiler flues quickly and the burner mixing tubes as a result. This action will can quickly extinguish any fire by lowering the ignition temperatures present in the mixing tubes.
The stack blower can also be useful to insure proper ignition of the burner after the car has sat for a period of time. It can be helpful to just crack open the stack blower valve such that a little bit of steam is directed down the exhaust flue. This starts a circulation of air into the mixing tubes, through the grate, up through the boiler flues, and out the exhaust duct. This airflow insures that when the firing up valve is opened to admit pilot fuel to the burner to light it off, the vaporized pilot fuel gases are quickly drawn through the mixing tubes and up through the burner grate to be ignited and burned on the topside of the grate. The burner lighting on pilot fuel reheats the vaporizer coil to improve vaporization. Then the firing up valve can be closed and the burner fuel valve opened. The airflow of the steam stack blower continues to insure the vaporized burner fuel is carried to the topside of the grate and properly burned. Once the burner is operating on burner fuel then the stack blower valve can be closed.
One word of caution in the proper use of the stack blower is suggested. The operation of the stack blower by design pulls large amounts of air through the mixing tubes, burner grate, and boiler flues. The air being pulled in will be at the ambient temperature of the environment. However the boiler will be hot (over 600º Fahrenheit for a boiler at 600 PSIG) and the cold blast of air drawn in by the stack blower may cause damage to the boiler. The flues will be at the same temperature as the boiler water surrounding them but when the airflow is increased the cooler air will quench the temperature of the flues. This may allow the flues to contract away from the holes in the flue sheet and allow the water under pressure to rain down on the hot grate. In a like manner the cool air being drawn in and through the hot burner grate can cause the grate to crack due to uneven airflow and temperatures of the grate casting metal. Thus a measured and conservative use of the stack blower is highly recommended. The stack blower should only be opened sufficiently to provide the minimum airflow needed and should be shut off as soon a possible.
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