« ForrigeFortsett »
through the tubes. Another bad air leak often occurs at the back connection when the arch rests wholly upon iron bars imbedded in the side walls. This leak, as has already been noted, is caused by the expansion of the boiler, which gradually pushes the arch away from the back head until, in the course of time, there will be a space of 5/8 in. and sometimes 34 in. between the head and the arch. The obvious remedy for this is an arch that will go and come with the movement of the boiler, and such an arch can be secured by building it in sections, as illustrated by Fig. 3, and then riveting a piece of angle iron to the boiler head, above
the top row of tubes for the upper ends of the sections to rest upon, as already described. It will be seen that within all possible range of boiler movement in either direction the arch will, with this construction, always remain close to the head.
Water Columns. Water columns should be so located as to bring the lower end of the gauge glass exactly on a level with the top of the upper row of tubes, thus always affording a perfect guide as to the depth of water over the tubes. Many gauge glasses are placed too low, and water tenders and firemen are often deceived by them unless their positions with relation to the tubes are carefully noted
The only safe plan for an engineer to pursue in taking charge of a steam plant is to seize the first opportunity for noting this relation. When he has washed out his boilers he may leave the top man-hole plates out while refilling them, and when the water stands at about four inches over the top row of tubes, the depth of water in the glass should be measured. He should do this with every boiler in the plant, and make a memorandum for each boiler. He will then know his bearings with regard to the safe height of water to be carried in the several gauge glasses. If he finds any of them are too low, he should lose no time
in having them altered to comform to the requirements of safety. The position of the lower gauge cock should be three inches above the top row of tubes.
In making connections for the water column plugged crosses should always be used in place of ells. Brass plugs are to be preferred if they can be obtained; but whether of brass or iron, they should always be well coated with a paste made of graphite and cylinder oil before they are screwed in. They can then be easily removed when washing out the boiler, so as to allow the scale, which is sure to form in the lower connection, to be cleaned out. The best point at which to connect the lower pipe with the boiler is in the lower part of the
-O THE ASYCROFT MFG.CO.
head just below the bottom row of tubes, and near the side of the boiler on which the water column is to stand; 174 or 1/2 in. pipe should be used in all cases. The top connection can be made either in the head near the top, or in the shell. A 34 or i in. drain pipe should be led into the ash pit, fitted with a good reli.
able valve which should be opened at frequent intervals to allow the mud and dirt to blow out of the water column and its connections. This is a very important point, and great care should be taken to keep the water column and all its connections thoroughly clean at all times.
One of the best indications that some portion of the
connections between the water glass and the boiler is choked or plugged with scale, is when there is no perceptible movement of the water in the glass. When the connections are free and the boiler is being fired,
there is always a slight movement of the water up and down in the glass, and when there is no perceptible movement it is time to look for the cause at once. Many instances of burned tubes have occurred, and
even explosions caused by low water in boilers while the gauge glass showed the water to be at a safe height. But owing to the connections having become plugged with scale, the water in the glass had no connection whatever with that in the boiler, and the water column was therefore worse than useless.
Steam Gauges. As water columns are made at present the steam gauge is usually connected at the top of the column. This makes a handsome and convenient connection, although theoretically the proper method would be to connect the steam gauge directly with the dome or the steam space of the shell. There should always be a trap or siphon in the gauge pipe in order