Maxims and Instructions for the Boiler Room / Useful to Engineers, Firemen & Mechanics; Relating to Steam Generators, Pumps, Appliances, Steam Heating, Practical Plumbing, etc.

by N. Hawkins

The compound is carried in this concentrated form, in calomine cans on the tender of each locomotive. A certain amount, according to the necessities of the case, is poured into the tender at the water tank at each filling. This amount is determined by analysis, and varies all the way from two to fifteen pints to two thousand gallons of water. The precipitating power of this compound may be taken roughly at ²⁄₃ of a pound of the carbonate of lime, or equivalent amount of other material, per pint of the compound. On their western lines where they are dealing with alkali waters and those containing sulphates, the company use merely 60 pounds of soda ash to a barrel of water. When the water is pumped into the boiler the heat completes the precipitation and aggregation of the particles, and this does away with all trouble of the tenders or injector tubes clogging up.

The case is an interesting one to stationary engineers, because where the water is pumped into the boiler from tanks the same compound can be used, provided the water contains the proper constituents to be precipitated by it; and where the water is taken from city water mains, it would be a simple matter to devise an apparatus to admit the compound to the feed pipes.

“Points” Relating to the Scaling of Steam Boilers.

The peculiarity about the sulphate of lime is that the colder the water the more of it will be held in solution. Water of ordinary temperature may hold as high as 7 per cent. of lime sulphate in solution, but when the temperature of the water is raised to the boiling point a portion of it is precipitated, leaving about .5 of one per cent. still in solution. Then as the temperature of the water is raised, still more of the substance is precipitated and this continues until a gauge pressure of 41 pounds has been reached which gives a temperature of about 200 degrees; at this point all the sulphate of lime has been precipitated. Many other scale forming substances act in a similar manner. This shows quite plainly that any temperature that can be produced by the use of exhaust steam would not be sufficient to cause the precipitation of all the substances which might be contained in the water.

That boiler incrustations are the immediate causes of the majority of steam boiler explosions is no longer a doubtable question.

Nearly all foreign matter held in solution in water, on first becoming separated by boiling, rises to the top in the form of what is commonly called scum, in which condition much of it may be removed by the surface blow-off. If not removed, however, the heavier particles will be attracted to each other until they have become sufficiently dense to fall to the bottom, where they will be deposited in the form of scale, covering the whole internal surface of the boiler below the water line, with a more or less perfect non-conductor of heat.

It is recorded that the engineer of the French ocean steamer St. Laurent omitted to remove a bar of zinc when repairing and cleaning out his boilers. On opening the boilers at the end of the voyage to his great surprise he found that the zinc had disappeared, but his boilers were entirely free from scale and the boiler plates not injured in the least.

It has been recently determined by some German experimenters that sugar effects a strong action upon boilers. It has an acid reaction upon the iron which dissolves it with a disengagement of hydrogen. The amount of damage done increases with the amount of sugar in the water. These results are worthy of note in sugar refineries and places where sugar sometimes finds its way into the boilers by means of the water supplied. The experimenters in question also find that zinc is strongly attacked by sugar; copper, tin, lead and aluminium are not attacked.

Two reasons, relating to incrustations, for not blowing out a boiler while under steam pressure may be given as follows: One is, that the foreign matter floating on top of the water will be deposited on the shell of the boiler as the water gradually subsides, and, second, the heated walls of the furnace will communicate a sufficiently high temperature to the boiler to dry and flake the sediment that would otherwise remain in the boiler in the shape of mud, which could easily be washed out were it not for the baking process.