Government of Bangladesh
The Boiler Act 1923
General Working of Boilers Instructions to Boiler Owners
These instructions should be frequently and carefully studied, with a view to keeping in mind the precautions to be observed, and the ordinary procedure to be followed in the safe working of boilers. These instructions must be framed and hung up in the Boiler Room.
PRECAUTIONS BEFORE STARTING THE FIRESBefore starting the fires in a boiler, the attendant should-
(1) see that there is sufficient water in the boiler and that the gauge cocks are working freely;
(2) ease safety values, or open cock on top of boiler to allow air to escape;
(3) see that the blow-off cock is fully closed and tight;
(4) see that the safety values and feed check value are free and workable;
(5) see that water is not leaking from any part of the boiler;
(6) note if the pressure gauge pointer is at zero;
(7) see that the feed [ump is in working order
He must not rely on the supposition that the water he has previously put in is still in the boiler , as it may have run out without his knowledge through a leak or open cock, nor can be sure that the gauge glass shows the true water-level until he has tested it. This is done in the following manner : shut off the lower gauge cock and empty the glass by the drain cock; then shut the drain cock and open the gauge cock; if everything is in order, the water will then rise in the glass to the same height as before.
RAISING STEAMIn getting up steam in all types of boilers the operation should be gradual as circumstances will allow. Nothing turns a new boiler into an old one sooner than getting up steam too quickly, Forcing the fires when starting work is liable to cause straining of the seams and tubes of the boiler. In the case of large boilers generally, steam should not be got up in less than six hours. Before getting up steam, the water-level should be observed to that water is at the prop height in the glass, the pressure gauge noted, and the safety valves tried to see that are free. The blow-off cock should be examined to see that it is completely shut and tight.
PRESSURE GAUGEThe pressure or steam gauge should be kept in order, and in a position as be easily seen by rage boiler attendant. There should be a plain mark on it showing the highest pressure for the boiler, and the dial should be kept ciean so the figures may easily be read.
STEAM PRESSUREOrdinarily the safety valve will prevent the steam from rising much above the working pressure, but if the steam gauge shows so raid an increase of pressure as to indicate of exceeding the highest limit, water should be immediately fed into the dampers partially closed in order to diminish the effect of the fire. If, however. the water has fallen so low that there is danger of an accident from this cause, the fires should be withdrawn before feeding in water, the safety valves eased and if the engine is at rest it should be started so as to reduce the pressure,
Te safety valves are provided to guard against overpressure. They should be moved by hand every day so as to prevent them from sticking. If moved only occasionally, they are liable to leak. The valve can be tested by slowly raising it a little, and when let down, it should close perfectly tight it should never be opened by a sudden knock or pull, If it does not close tight, turn it on its seat until it fits, or when its construction does not permit this, raise it slowly a few times and let it down again, but on no account must the valve be screwed down further or loaded morc than what has been allowed by the Inspector. Safety valves must never be overloaded and spring valves should have ferrules or other provision against the valves being screwed down too far. in case of an accident resulting from wilful overloading the culprit might be held criminally responsible at the official inquiry or inquest.
LOW WATER SAFETY VALVESIf there is a low water safety valve, test it occasionally by lowering the water level to see that the valve begins to blow at the right point. It should give warning BEFORE the water level has sunk too and before damage can be done. When the boiler is opened, examine the floats and lever and see that they are free and that they give the valve fill rise. With the ordinary type of high-steam and low-water safety valve the float should be down at its lowest position and the valve fill open when the boiler is empty.
THE WATER GAUGESThese will be kept in best order by frequently blowing through. The cocks are thus kept in good working condition without leaking. Blow through the drain cock at the bottom of the gauge, and shut and open the steam and water cocks every few hours. These cocks should be blow through more frequently when the water is dirty. Should either of the passages become choked, or whenever the water in the gauge glass moves sluggishly, the passages must be cleaned. This is best done with a wire. The gauge glass is so arranged that its top cock connects with the steam space and its bottom cock is below the water line. The water line will ordinarily be near the middle of the glass tube. Always test the lass water gauges thoroughly the first thing in ordinarily and at the commencement of every shift. This is done by first opening the drain cock and then shutting the upper cock which should give water; the upper cock should then be opened and the bottom cock closed which should give steam; during this test the drain cock should be kept open.
If water and team do not appear in proper order, the cocks are choked and the passages should be cleaned. To lessen the risk of breaking the gauge glass, the water cock should always be reopened after the steam cock.
Guage glasses with a narrow white stripe running the whole length of the glass on the side next the boiler are recommended, as they show the water line more clearly, especially when the water is dirty.
The Government Boiler Regulations require every water gauge glass to be fitted with a guard to provent injury to the attendants. See that it is always in place, and clean, when there is steam in the boiler.
SPECIAL NOTEIt does not follow that there is plenty of water in the boiler because there is plenty of water in the gauge glass. The passages may be choked, and empty gaugte glasses are sometimes mistaken for full ones, and explosions have resulted therefore. Hence, the importance of keeping the gauge cocks perfectly tight and clean and of blowing through the test cocks frequently.
A large number of accidents have been due to inoperative water gauges, and to negligence of the attendant in not carefully reading the water level.
THE BLOW-OFF COCKThe blow-off cocks should be used daily if the water is at alll dirty or sedimentary especilly with locomotive type and vertical boilers, as their narrow water spaces are liable to get choked with mud, which soon hardens into a solid mass, The amunt of water to be blown out depends on the size of the boiler and can be determined only from experience, When blowing out the best result if the water been at rest for some time (say before engine is started) thus giving the sediment time to settle; if the feed water is clean merely turn the cock round.
THE SCUM COCKWhen scum cocks are fitted, if the feed water is dirty, a little should be blown off daily; if the water is clean, merely turn the cock round. Before opening the scum cock see that water is at the height indicated by the water-level pointer, otherwise the scrumming will be ineffective. water should be blown from the surface through the scum cock when steam is being drawn off, i. e.; when the engine or other machinery is working.
MANHOLE AND OTHER DOOR JOINTSWhen making such joints the jointng materials should never be of round-sectioned packing. Car must be taken that the spigot of the door is centrally placed in the hole as many accidents have resulted from packing being blown out between the spigot and side of hole, even when the clearance was only 1/8th of an inch. The musts must be carefully and evenly tightened. Further tightening should be made during the processor heating up the boiler when raising steam.
STEAM PIPESWhen properly arranged, should give no trouble. Frequently, however, they are so designed as to contain pockets, which, while out of use, condensed steam accumulates. Such water is exceedingly dangerous and great care should be taken to see that the pipes are properly drained before the stop valve IS OPENED, otherwise WATER HAMMER will take place even with the best designed steam pipes, and disastrous explosions, gausing loss of life and property, may occur.
SCALE AND GREASERoughly speaking, scale offers a hundred times as much resistance to the passage of heat as does a similar, thickness of steel or iron. A half-inch furnace plate covered with 1/10th inch scale is as efficient a heat retarder as a steel furnace 10 inches thick. Grease is about ten times worse than scale. In a boiler at work the temperature of a clean furnace plate is only slightly in excess of that of the water in the boiler; but if scale or grease is interposed between the water and the plate. the latter acquires a temperature more nearly approximating that of the flame with which it is in contact. If the fire is fierce (artificial draught) the furnace tube may grow so hot that it elongates considerably. If, in addition, cold air is admitted during each firing, a concerting action of the furnace takes place which is one of the worst causes of boiler wear and tear.
WEAR AND TEARCan be reduce and the life of a boiler prolonged if scale and grease are prevented from accumulating in a boiler. The combined effect of scale or grease and artificial draught are disastrous. Scale or grease also causes waste of fuel.
GREASEA mixture of sedimentary water, soda, and grease produces an adhesive scum. Where this is suspected, the water-level should never be lowered below the furnace top, unless the boiler is afterwards entered and this scum cleaned off the furnace plate before firing again.
SCALE REMOVALThe customary method is not a satisfactory one. The boiler is emptied and then cooled down by opening all the manholes, and the result is that the scale, which would otherwise be soft, hardens through contact with the air, and requires laborious clipping off.
A very effective, but slower method, is to retain the water in the boiler until cool. and not to run it out until the men are ready to enter the boiler with water hose, brushes and scrapers. The scale will then be soft and easily removable.
If time is a consideration, the coolng can be accelerated by addng cold feed to the hot water in the boiler and slowly renning off the cooled water. Another method is to blow off the boiler with the lowest possible pressure (not more than 20 Ibs.) and to keep it closed until cold. The scale will then be easily removed.
PRECAUTIONS TO BE TAKEN WHEN USING GAS OR OIL FUELOil or Gas Fired Boilers should not be provided with flue dampers, but if fitted, they should be kept locked in an open position. Before lighting the burner, any oil vapour or gas which may have collected should be expelled by flushing the flues with a strong current of air. When a fan is provided this should be run for a few minutes before the oil fuel or Gas is turned on and ignited. Should the flame at any time go out the Fuel Supply should be turned off and the flushing process carried out before the Fuel is again turned on and the burner re-ignited.
TREATMENT OF FEED WATERMany feed required soda or other chemicals to arrest corrosion or to change the nature of the scale. There is NO HARMLESS CHEMICAL which will remove scale or sediment when it has once got into the boiler, and the only effective process is to purify the feed water before it enters the boiler. By this means the sediment, and generally, too, the added chemicals can be deposited in tanks or in filters, and therefore never goes into the boiler. Excepting when the water obtainable is very good, water-purifying apparatus ought to pay any boiler owner particularly at those woks where three or more boilers are in constant work. Boiler owners wishing to have definite advice as to the best treatment of their feed water should have it analyzed at some chemical laboratory and ascertain the best treatment in the particular circumstances.
Special attention is drawn to the not infrequent but VERY BAD practice of allowing the waste steam from the engine cylinders or pumps to be drained into the Boiler Feed Water Tanks. The waste steam from cylinders is always mixed with a certaqin amount of only matter, which will be deposited in the feed water tanks and ultimately be pumped into the boiler, with possibly disastrous results, as it will be obvious to every careful boiler attendant that should the oil be deposited on the furnace crowns, they may become overheated and collapse.
It should be the first care of the boiler owner, and the boiler attendant to see the feed water is kept as pure as possible. Impure feed water means additional expense on the upkeep of the boiler.