Boiler pressure

“ If the pressure be taken at 120 lbs., instead of 20 lbs., the saving will be 13.1 per cent, showing a slight diminution in the economy effected by heating the feed water when a high boiler pressure is employed. ”

“ Uniting with the body of water in the combining tube, it imparts to it a large share of its speed, and the body of water thus set in motion, operating against a comparatively small area of boiler pressure, is able to overcome it and pass into the boiler. The weight of the water to which steam imparts its velocity gives it a momentum that is greater in the small area in which its force is exerted than the boiler pressure, although its force has actually been derived from the boiler pressure itself. ”

“ It is fortunate, however, that the error is usually upon the safe side of indicating more than the actual pressure.
Any boiler that has been standing idle for a few weeks or months is a dangerous thing to enter, and no one should attempt it until it has been thoroughly ventilated by taking off all the man hole and hand-hole plates and throwing water into it. This is due to the presence of a gas which is generated from the refuse and mud, or scale, which, to a greater or less degree, remains in all boilers. Contact with fire is certain to result in an explosion. ”

“ A high pressure insures tranquillity at the surface, and the steam itself being more dense it comes away in a more compact form, and the ebullition at the surface is no greater than at a lower pressure. When a boiler foams it is best usually to close the throttle to check the flow, and that keeps up the pressure and lessens the sudden delivery. ”

“ To fill the boiler to three gauges and then shut off the feed until the water level is again down, the exhaust steam, after it has heated the water standing in heater, passes off without leaving any of its heat, and then turning on the feed water again much faster than needed, the water has not time to take up so much heat as if the feed were slow and regular. Much bad effect on the boiler is due to the difference in temperature at the time when the feed is off and on.
Never calk a boiler under steam pressure unless you are tired of life. ”

“ The water is forced out very rapidly with this pressure, and the last thing that comes out is the steam. This steam keeps the entire boiler hot till everything is blown out, and the result is that all the dirt, sediment and lime is baked solid on the tubes and side of firebox. But you say you know enough to not blow off at 50 pounds pressure. Well, we will say 5 pounds, then. You will admit that the boiler is not cold by any means, even at only 5 pounds, and if you know enough not to blow off at 50 pounds, you certainly know that at 5 pounds pressure the damage is not entirely avoided. ”

“ The cylinders of which the boiler is composed are so small as to bear a greater pressure than could be produced by the quantity of fire beneath the boiler; and if any one of these cylinders should be injured by violence, or any other way, it would become merely a safety valve to the rest. We never, with the greatest pressure, burst, rent, or injured our boiler ”

“ If the safety valve is closed, it may retain the pressure thus created for a short time, and even when it is open the escape may not be sufficiently rapid to remove all impediment; there may therefore exist momentarily within the boiler pressures of various force, varying from that which can just lift the safety-valve up to that which is sufficient, if exerted during an extremely small space of time, to tear open the boiler itself. ”

“ If a boiler should be found with an excessively high pressure, it would be one of the worst things to do to start the safety valve from its seat unless extra weight was added, for should the valve once start, it would so suddenly relieve the boiler of such a volume of steam as would cause a rush of water to the opening, and by a blow, just the same as in water hammer, rupture the boiler. ”

“ Again it has been asserted that the steam when remaining quite still in the boiler becomes heated much beyond the temperature due to the pressure; and that therefore when it is stirred or mixed or brought more in contact with the water by the opening of a valve or other cause, the water evaporates so rapidly as to produce an excessive pressure by accumulation of steam. ”

“ Amongst the essentials are a receptacle capable of containing the water and the steam produced by its evaporation, and strong enough continuously to withstand with safety the highest pressure of steam for which the boiler is intended. Another essential is a furnace for burning the fuel, and a further one is the provision of a sufficiency of heating surface for the transmission of the heat produced by the combustion of the fuel to the water which is required to be evaporated. ”

“ Almost the only danger from explosion of a boiler is from not having sufficient water in the boiler. The boiler is filled in the first place, as has already been explained, by hand through a funnel at the filler plug, or by a force pump. The water should stand an inch and a half in the glass of the water gauge before the fire is started. It should be heated up slowly so as not to strain the boiler or connections. When the steam pressure as shown by the steam gauge is ten or fifteen pounds, the blower may be used to increase the draft. ”

“ Well, to find the safe working pressure of a boiler it is first necessary to find the total pressure necessary to burst the boiler. It requires about twice as much pressure to tear the ends out of a boiler as it does to burst the shell, and as the weakest point is the basis for determining the safe pressure, we will make use of the shell only.
We will take for example a steel boiler 32 inches in diameter and 6 ft. long, 3/8 in. thick, tensile strength 60,000 lbs. The total pressure required to burst this shell would be the area exposed times the pressure. ”

“ In guarding against explosion it is conceded that the main reliance is to have the boiler made strong enough to stand both the regular load or any unexpected strain caused by the stoppage of the engine; it is also the tendency of the times to proceed towards higher and higher figures in steam pressure, until now it is not unfrequent to see 150 lbs. to the square inch indicated by the gauge; the larger the boiler, also, the more economically it can be run and this, as in the two cases before cited, requires extra precautions in building the boiler with great regard to strength in every part. ”

“ For example, a boiler whose ordinary working pressure is one hundred pounds to the square inch, which may give an aggregate on the whole surface of five millions of pounds, would not give way, perhaps, if that pressure were gradually and evenly increased to thirty millions. But if the water is allowed to get so low that some part of the plate exposed to the fire is no longer covered with it, that part will directly become far hotter than the water or the mass of the steam,—dry steam having no more power to carry away the excess of heat than so much air. ”

“ Besides, it is well to bear in mind that the tightness of a boiler under test is no guarantee of its tightness after it is got to work. In a word, as far as new boilers are concerned, the application of hydraulic pressure unaccompanied by careful inspection and gaugings may be almost worthless, while with these additions it may be extremely valuable, especially in the case of boilers of peculiar shape, and is a precaution that should not be neglected. ”

“ Where the water throughout the boiler is at the temperature of the steam contained, a condition to be secured only by proper circulation, danger from internal pitting is minimized, or at least limited only to effects of the water fed the boiler. Where the water in any portion of the boiler is lower than the temperature of the steam corresponding to the pressure carried, whether the fact that such lower temperatures exist as a result of lack of circulation, or because of intentional design, internal pitting or corrosion will almost invariably result. ”

“ The fact that a firebox is no pleasant workshop may have had something to do with it. If your flues have been leaking badly, and you have expanded them, it would be well to test your boiler with cold water pressure to make sure that you have a good job.
How are you going to test your boiler? If you can attach to a hydrant, do so, and when you have given your boiler all the pressure you want, you can then examine your flues carefully, and should you find any seeping of water, you can use your beader lightly untill such leaks are stopped. ”

“ A.--No; it is found to be productive of injury to the boiler by the violent alternations of temperature it occasions, as at some times cold air impinges on the iron of the boiler, and at other times flame,--just as there happens to be smoke or no smoke emitted by the furnace. Boilers, therefore, operating upon this principle, speedily become leaky, and are much worn by oxidation, so that, if the pressure is considerable, they are liable to explode. It is very difficult to apportion the quantity of air admitted, to the varying wants of the fire ”

“ As the flat ends of such boilers are always being sprung by each alternation of pressure into a more or less spherical shape, as shown by the elastic model exhibited, this consideration no doubt led to the ends being made hemispherical, as shown in Pg 21 Fig. 25; and plain cylindrical boilers with these hemispherical ends are now so commonly used that they far outnumber any other form of boiler. Their shape renders them very strong, as the whole of the iron is in simple tension, and internal pressure has no tendency to alter the shape, as is shown by the elastic model exhibited. ”

“ Steam pressure may be guarded against by a safety valve; but as this may become set fast in a little time, it would be far better to avoid all chance of steam accumulation by such an arrangement as that shown in Fig. 55, where the circulating boiler is placed within an open-topped boiler behind the kitchen fire, and only receives its heat through the hot water surrounding it, and therefore cannot itself become sufficiently hot to generate steam. ”

“ Explosions are seldom caused by a sudden increase of pressure, but rather by the pressure gradually mounting to the bursting point, when of course the effect is sudden enough. Nor is it necessary in many cases to look for much increase of pressure as the cause of explosion; for it is far more often the case that the strength of the boiler has gradually degenerated by wear or corrosion, until unable to bear even the ordinary working pressure. ”

“ The steam pressure of the repaired boiler is usually fixed at about a hundred and twenty-five pounds per square inch. The capacity of each boiler is very great, and the composite power of the whole set formidable; if one of them should happen to explode the result would indeed be disastrous. A small staff of men superintends them by day and night, and greater care is taken of them than was the case formerly. I can remember when the shed was several times within a hair’s breadth of being blown up and forty or fifty men hurled to perdition. ”

“ A pipe C is used for heating the liquor by means of waste steam at the commencement of the operation. The grass is fed into the boiler at the opening D. At E E are gauges for showing the height of the liquor in the boiler, F F F are pipes for the supply of steam, strong ley, and water, and the door G is for the discharge of the boiled grass. Each boiler is capable of holding 3 tons of esparto, and the boiling is completed in about two and a half hours, at [46] a pressure of from 35 to 40 lbs. per square inch. It is said that the boiler effects a saving both in time and the amount of soda used. ”

“ In case the boiler feed should stop working, however, the hot well is provided with a pipe of large diameter, and called the overboard discharge pipe, so that the water of condensation may not accumulate a pressure in the hot well if the boiler feed ceases. ”

“ The boiler is to be filled with straw and alkaline solution and then closed fluid and steam-tight. The boiler is made to revolve slowly, say about one or two revolutions per minute, and the steam is to be admitted. I find it desirable to keep up the heat and pressure during about three hours after the pressure above mentioned has been obtained, when the process of boiling is complete. A steam-gauge proper y fixed upon the boiler will enable one to ascertain when the pressure has attained the required degree. ”

“ It prevents too high a pressure for accumulating in the boiler when there is plenty of water; but when the water gets low the safety valve may only hasten the explosion by relieving some of the pressure and allowing superheated water to burst suddenly into steam, thus vastly expanding instantly. ”

“ It was formerly required for each marine boiler to have a small valve loaded with a weight to a few pounds per square inch above the working pressure, so that in case of the safety valves sticking fast and the gauge being false, an alarm might be given when there was an excess of pressure. ”

“ This is an investment—other kinds of boilers are finally permitted to add a value to the junk pile by rusting, pitting, and other useless decadences.
11. No danger in a boiler where the fire chamber is entirely surrounded by water and steam surfaces; and when the boiler stands low and therefore well away from the joists and woodwork. Boilers are generally tested for 80 pounds pressure, but to operate them 2 pounds ought to be enough, though 1 to 5 is the usual bill-of-fare.
Steam boilers should have a relief valve—when pressure builds up to 10 or 11 pounds. ”

“ A sketch of a boiler Pg 31 with collapsed flue is given in Fig. 42, which exploded at Burton-on-Trent in 1865; and it is selected from many others because it was a new boiler, well made and mounted, and was a good example of the weakness of a large tube to resist high external pressure when made of great length without the support of strengthening rings.
There are a great many advantages in the tubular boiler internally fired. The shell which is exposed to the greatest tension is not also exposed to the first action of the fire. ”