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nipple entering the boiler should have a long thread cut on the end which screws into the sheet, and to this end inside the boiler there should be connected another pipe which shall extend horizontally at least twothirds of the length of the boiler, resting on top of the tubes, and then discharge. Or, what is still better, allow the internal pipe to extend from the entering nipple at the front end to within a few inches of the back head, then at right angles across the top of the tubes to the other side, and from there discharge downward. By this method the feed water is heated to nearly, if not quite, the temperature of the water in the boiler before it is discharged. One of the objections to this system is the liability of the pipe inside the boiler to become filled with scale and finally plugged entirely. In such cases the only remedy is to replace it with new pipe. But the great advantage of having the water thoroughly heated before being discharged into the boiler will much more than compensate for the extra expense of piping, and the general idea of introducing the feed water at the top instead of at the bottom of the boiler is therefore recommended as being the best.
The diameter of teed pipes ranges from 1 in. fo: small sized boilers, up to 1/2 and 2 in. for boilers of 54 to 72 in. in diameter. It is not good policy to have the feed pipe larger than necessary for the capacity of the boiler; because it then acts as a sort of cooling reservoir for the feed water, and may cause considerable loss of heat.
For batteries of two or more boilers it is necessary to run a main feed header, with branch pipes leading to each boiler. The header should be large enough to supply all the boilers at the same time, should it ever
become necessary to do so.
The header can be run along the front of the boilers just above the fire doors with the branch pipes running up on either side, clear of the Aue doors and entering the front connection, or smoke arch, and the boiler head at a point two inches above the tubes. There should always be a valve in each branch pipe between the check valve and the header for the purpose of regulating the supply of water to each boiler, and also for shutting off the . pump pressure in case of needed repairs to the check valve. Another valve should be placed between the check valve and the boiler.. By this arrangement it is always possible to get at the check valve when it is out of order.
Blow off Pipes. Blow off pipes should always be connected with the lowest part of the water space of a boiler. If there is a mud-drum, then of course the blow off should be connected with it; but if there is no mud-drum, the blow off should connect with the bottom of the shell, near the back head, extend downwards to the floor of the combustion chamber, and thence horizontally .out through the back wall, where the blow off cock can be located.
The best blow off cocks are the asbestos packed iron-body plug cocks, which are durable and safe. A globe valve should never be used in a blow off pipe, because the scale and dirt will lodge in it and prevent its being closed tightly. A straight way or gate valve is not so bad, but an asbestos packed plug cock is undoubtedly the best and safest.
In order to protect the blow off pipe from the intense heat, a shield consisting of a piece of larger pipe can be slipped over the vertical part before it is connected.
Blow off cocks should be opened for a few seconds once or twice a day, to allow the scale and mud to be blown out. If neglected too long they are liable to become filled with scale and burn out. A plan which is said to give good results is to connect a tee in the horizontal part of the pipe, and from this tee run a i in.
pipe to a point in the back head at the water level. It is claimed that this will cause a circulation of water in the pipe and prevent the formation of scale.
A surface blow off is a great advantage, especially if the water is muddy or liable to foam. By having the surface blow off connected on a level with the
water line a large amount of mud and other matter which is kept on the surface by the constant ebullition can be blown out.
A combination surface blow off, bottom blow off, and circulating system can be arranged by a connection such as illustrated in Fig. 9. By closing cock A and opening cocks' B and C the bottom blow off is put in operation; by closing B and opening A and C the surface blow off is started, and by closing C and leaving A and B open the device will act as a circulating system. The pipe should be of the same size throughout. Blow off pipes should be of ample size, never less than 1% in., and from that to 242 in., depending upon the size of the boiler.
Feed Pumps and Injectors. The belt driven power pump is the most economical boiler feeder, but is not
the most convenient nor the safest. When the engine stops, the pump stops also, and sometimes it happens that the belt gives way and the pump stops at just
the time when the boiler is being worked the hardest.
The modern double acting steam pump, of which there are many different makes to choose from, is without doubt the most reliable boiler feeding appliance and the one best adapted to all circumstances and conditions, although it is not economical in the
use of steam, since the principle of expansion cannot be carried out with the pump as with the engine.
In selecting a feed pump care should be exercised to see that it is of the proper size and capacity to supply the maximum quantity of water that the boiler car evaporate. This may be ascertained by taking into consideration the amount of heating surface and the required consumption of coal per square foot of grate suiface per hour. First, take the coal consumption. Assume the boiler to have 30 sq. ft. of grate surface,