« ΠροηγούμενηΣυνέχεια »
a large air chamber on the discharge pipe, near the plunger, to prevent shocks and preserve the valves. Screw pumps and rotary pumps do not require air chambers because they discharge a steady stream of water. The suction pipe to any type of pump must be air-tight, since otherwise the pump cannot raise the water.
A foot-valve at the base of a high suction pipe will hold it full of water in case a small air leak should develop near the top of the pipe.
In all pumps, whether lifting, force, steam, single-acting, double-acting, or centrifugal, the number of foot-pounds of work performed by the pump is equal to the weight of the water discharged, in pounds, multiplied by the vertical distance, in feet, between the level of the water in the well or source and the point of discharge, plus the work done in overcoming the friction and other resistances. (It is assumed that the water is delivered with practically no velocity.)
To find the discharge of a pump, in gallons per minute: Let T= piston travel, in feet per minute;
d = diameter of cylinder, in inches;
G = number of U. S. gallons discharged per minute. Then, G= .03264 T ď2.
To find the horsepower of a pump, use the following formula, in which T and d are the same as above, and his the vertical distance. in feet, between the level of the water at the source and the point of discharge.
H. P.=.00033724 Gh = .00001238 Td2 h.
In both the above formulas, allowance has been made for friction, leakage, etc.
The duty of a pump is the number of foot-pounds of work actually done for 100 lb. of coal burned.
W weight of coal burned, in pounds.
The Hydraulic Ram.-This machine is employed to raise water to a point higher than the source of supply; it is chiefly used where a large flow of water with a low fall is obtainable, and raises part of the water that operates it. The efficiency
varies with the ratio of the rise of the discharge to the fall of the drive pipe, about as follows:
Ratio of lift to fall: 4, 6, 8, 10, 12, 14, 16, 18, 20, 22, 24, 26. Per cent. efficiency: 72, 61, 52, 44, 37, 31, 25, 19, 14, 9, 4, 0. To obtain the highest efficiency with any fall, the dash valve should be adjusted to close at the instant the water in the drive pipe has attained its maximum velocity.
A ram having a discharge pipe 80 to 100 ft. long will deliver about the quantity supplied to a height about 5 times the fall; or the quantity supplied to a height of 10 times the fall.
SIZES OF PIPE FOR RAMS.
If the pipes are lead, the drive pipe should be of the A grade, for diameters up to 2 in., and cast or wrought iron for greater diameters. The discharge pipe, if lead, should be of the B grade for rises of 50 ft. or less, and of the A grade for rises between 50 and 100 ft. For falls greater than 10 ft. or rises of more than 100 ft. the pipe must be heavier than just given. The length of drive pipe should be from 25 to 50 ft. If the discharge pipe is very long (say mi.), a larger size than given in the table should be used. With a given supply of water under a great fall, the ram need not be as large as for the same quantity of water under a less fall. When large quantities of water are to be raised, it is better to increase the number of rams, in preference to Several rams may be
having one of very large capacity. set so as to deliver into one discharge pipe, each having a separate drive pipe. The diameter of the delivery pipe is usually about of the diameter of the drive pipe. The highest efficiency of a ram is obtained with the specified length and size of drive pipe when the weight and length of stroke of the valve are properly proportioned.
1-4 3 7
12 -25 20-40 25-75
Size of Pipe.
Cisterns.-These are used to store rain water underground, for use in country buildings. For an ordinary house with 8 rooms or less, located in a climate where the rainfall is not less than 30 in. per annum, and where very long droughts do not occur, a brick cistern 5 ft. in diameter and 7 ft. deep will be large enough for a family of 10 people. Larger buildings should be provided with two or more cisterns.
Cistern filters are essential in all cases. Fig. 1 shows an excellent and simple form, which may be built a few feet
away from the cistern, and connected to it by the pipe f. The filter well is built of brick, laid in 1-to-1 Portland cement mortar, and is divided into two compartments by a parti. tion slab a of slate or flagstone. The bottom is inclined so that the sediment will collect at d. The chamber B has a perfor
ated bottom b, on which is placed a course of gravel and then clean sand topped with gravel nearly up to the level of the discharge pipe f. Rain water enters A through the pipe c, and deposits any mud that it may contain at d. Any overflow in A is discharged through pipe e. The water flows upwards through the sand in chamber B, which clarifies it. The filter may be easily cleaned by stopping up f, pouring water into B, and pump. ing out the mud and dirty water from A. Renewal of the filtering material is thus seldom necessary.
House Tanks.-Water-storage tanks located on the roof are generally constructed of cedar or cypress and are slightly conical. They are generally knocked down when shipped, and should be set up and filled with water as soon as delivered. A good solid foundation should be provided for a house tank, and the weight of the tank should not be allowed to rest on the chimes (that part of the stave that projects below the bottom), but should rest on the tank bottom.
The capacity of cylindrical tanks may be found by squar ing the diameter, in feet, and multiplying the product by .7854, then multiplying the area by the height of the tank, in feet. The product will be the capacity of the tanks, in cubic feet. To find the number of U. S. gallons, multiply the number of cubic feet by 7.48.
EXAMPLE.-What is the capacity of a tank 6 ft. in diameter and 5 ft. deep: (a) in cu. ft.? (b) in U. S. gal.?
SOLUTION. (a) 6 X 6 X .7854 X 5 = 141.40 cu. ft. (b) 141.40 X 7.48 1,057.67 U. S. gal.
The table "Sizes of Wooden Tanks" gives the stock sizes and capacity of ordinary tapered wooden hooped tanks up to 2,820 gal. capacity.
lined with sheet lead, or tinned copper. To obviate the use of heavy planking in the construction of such tanks, tie-rods a are used to rigidly tie together the end and side braces, or stiffeners b, b, which are secured by mortise and tenon joints to the timbers c, c on which the bottom planking of the tank