Boys' Book of Model Boats

by Raymond F. Yates

The cylinder is merely a piece of stovepipe iron bent to shape and provided with several air-holes at the burner end. To start the burner, the vaporizing coils must first be heated in an auxiliary flame. The flame of an ordinary blow-torch is suitable for this purpose. After the coils have become sufficiently hot the valve at the top of the gasolene-tank is opened, and this causes a stream of gasolene vapor to issue at the nipple. This produces a hot flame at the center of the vaporizing coils, and in this way the coils are kept hot. The purpose of heating these coils is further to vaporize the gasolene as it passes through them on the way to the burner. Once started, the action of the burner is entirely automatic. The vaporizing coils are made of Shelby steel tubing with an internal diameter of ¹/₈ inch.

It will be seen that the flame from the gasolene-torch is blown through the center of the boiler coils B. Thus, any water passing through these boiler coils is instantly converted into steam. In other words, the water "flashes" into steam. The heat of the blow-torch is so great that most of the boiler coils are maintained at red heat even while the water is passing through them.

Notice the water-tank G. A little scoop, formed by a pipe of small diameter, protrudes through the bottom of the boat, so that the forward motion of the boat will cause water to rise in the tank G. An overflow is also provided, so that, should the water not be sucked out of the tank quickly enough, it will not flood the boat. The overflow pipe hangs off the side of the boat.

The water pump E sucks water from the tank, and pumps it through the check-valve K (this valve permits water to pass in one direction only) into the boiler coils. The boiler coils, being red-hot, cause the water to flash into steam the instant it reaches them. By the time the steam has reached the opposite end of the boiler coils, it is no longer steam, but a hot, dry gas at a terrific pressure. From the boiler coils the steam passes into the steam-chest of the engine, and thence into the cylinder, where it expands, delivering its energy to the piston.

It will be seen that the water-pump E is geared to the engine. Owing to this, it is necessary to start the water circulating through the boiler coils by the hand pump F. This hand pump forces water through the boiler coils just as the power pump does. After the hand pump is started the engine is turned over a few times until it starts. The valve H is then closed, which cuts the starting pump F entirely out of the system, because when the engine starts it also drives the water pump E, and therefore the action becomes entirely automatic.

The relief-cock L is placed in the system to be used if the engine stalls. By opening the relief-cock the pressure in the complete system is immediately relieved. At all other times the relief-cock is closed.

A second pump, I, is also included in the system. This, like the water-pump, is geared to the engine and driven by it. It is the duty of this pump to convey oil from the lubricating tank M into the steam feed-pipe just before it enters the steam-chest. In this way the live superheated steam carries a certain amount of lubricating oil with it in the cylinder.

Owing to the high temperature of the superheated steam, it is impossible to use brass cylinders on the steam-engines employed with flash steam systems. Steel seems to be the only cheap metal that is capable of withstanding the attack of flash steam. Brass is out of the question, since its surface will pit badly after it is in use a short time.

The boiler of a flash steam plant is covered with sheet iron so as to prevent drafts of air from deflecting the flame from the center of the boiler coils. The cover is provided with ventilators, so that the burner will not be smothered. If enough oxygen does not enter the interior of the boiler coils, poor combustion will result, and the gasolene flame will not develop its maximum heat. Upon referring again to the diagram, it will be seen that the exhaust steam pipe from the engine discharges into the stack of the boiler covering. This discharge greatly facilitates the circulation of air through the boiler coils.

After a flash steam plant has been started it will work automatically, providing all the parts are in good running order. Flash steam plants, however, are difficult to get in the proper adjustment, and once adjusted they are easily disturbed by minor causes. Owing to the fact that every square inch of surface in the flash coils is heating surface, the amount of water supplied to the boiler must be exactly what is needed. The heat must also be regulated so that the temperature of the steam will just meet the engine's needs. Many times an increase in heat causes the steam to reach such a temperature that it will burn up the lubricating oil before it reaches the cylinder of the engine. This is liable to cause trouble, because sticking is apt to occur.