« PreviousContinue »
ducted to the under side of the grate of the producer, and is sucked through with the air.
Owing to the resistance offered by the fuel, scrubber, and other parts of the plant to the passage of the gas, its pressure on reaching the engine in considerably below the atmospheric pressure. This causes a decrease in the weight of the charge taken to the engine, and so makes the power of the engine less than when pressure gas is used. In order to get the high compression which is necessary to ensure ignition with a weak gas supplied at a low pressure, the clearance in the engine using suction gas is smaller than in other engines using the same cycle. It is not safe to use such an engine with illuminating gas, as the pressures resulting from explosion would be excessive. When in some cases illuminating gas is used to start the engine, a special device is employed to exhaust some of the charge during the compression period, and so to reduce the compression pressure.
FIG. 2. DIAGRAM OF SUCTION-TYPE PRODUCER PLANT.
An efficient producer of either the pressure or suction type will waste not more than fifteen to twenty per cent of the heat of combustion of the coal in converting it into gas-that is, the gas, on burning, will give up eighty to eighty-five per cent of the heat of combustion of the coal. Its efficiency exceeds that of a steam boiler. If the gas produced is a weak one, it is produced in greater volume, and it has to be mixed with a much smaller volume of air than is required for illuminating gas. For example, ordinary coal gas must have at least six parts of air to one of gas, whereas producer gas requires a minimum of about one and a-quarter parts of air to one part of gas.
foot of the explosive mixture much more nearly equal than the heats of combustion per cubic foot of the fuel. Thus, when mixed with just sufficient air for complete combustion, natural gas, coal gas, and water gas will all give up about 90 B.T.U. per cubic foot of the explosive mixture, while producer gas gives up about 65 B.T.U. An engine will consequently develop about the same power whether using natural gas, coal gas, or water gas; when using producer gas, on the other hand, it will develop considerably less power.
by CARL S. DOW.
NE of the most common methods of fastening parts of machinery is by means of the bolt. Various kinds of bolts are used around engines, in such places as on the cylinder head, connecting-rod ends, bearings, etc. In general machine work, the bolt is used to such an extent that some companies devote themselves to making nothing but bolts and nuts, turning out thousands daily.
The screw is a means of transmitting power, especially if the pressure is great and the velocity very low. This is often seen in screw-jacks, testing machines, presses, etc. The carriage of a lathe used for screw-cutting is moved by the lead
In Chalk Talk No. XXIV, we discussed a curve called a helix, and found that it is a curve generated by the movement of a point on the surface of a cylinder, the movement being such that the distance traversed by the point while passing around the cylinder is equal to the pitch. Now, if we cut a groove on a metal cylinder, the groove following the helix, the metal remaining between the grooves will be the thread. A cylinder having a thread cut in this manner is called a bolt or a screw. To make the bolt useful under some conditions a nut must be made to fit the thread. This is a square or hexagonal piece of metal with a helical groove cut within it.
Kinds of Threads
There are three kinds of threads in common use: the "V thread," the "U. S. (80)
Standard," and the "Square." Of these forms, the V is the simplest and most common, especially for soft metals like brass. The cross-section of this thread is an equilateral triangle, as shown in Fig. 1. The angle between the two sides of the thread is 60°. The pitch is the distance from the top of one thread to the top of the next. A simple calculation based on geometry will prove that the depth is equal to the pitch x .866 (depth : V1 −.5).
Thread Not for Hard Usage
The V thread is not suited to much pressure or hard usage. The sharp edges are liable to be broken, and the deep, sharp groove makes the bolt weak. Moreover, the sharp edges make it difficult to put on the nut.
United States Standard
The United States Standard thread, sometimes called the "Franklin Institute," or "Sellers," has these tops cut off; that is, the tops are flattened. Also, the groove does not come to a point, but is flat at the bottom. The sides form the same angle as the V (60°), as shown in Fig. 2. The width of this flat portion is one-eighth of the pitch. If this amount is taken from the top and from the bottom, the real depth is three-quarters of the depth of the V thread, or .65 of the pitch (.866 × 3⁄44 = = .65).
List of Standard Threads
Of course, it is possible to cut a thread of almost any size on a given cylinder; but, in order that everyone may know the pitch of the thread on a bolt of given
(Rights of Publication Reserved by Author.)
thread allows power to be transmitted in either direction, since the sides are perpendicular and therefore alike. This form is very simple, the grooves being like the threads, as shown in Fig. 3.
The square thread is often modified somewhat. If power is to be transmitted in one direction only, one side is made perpendicular and the other at an angle. in order to give greater strength at the root. This is shown in Fig. 4. The angle is not made to any standard, but 30 is about average practice.
The so-called Acme thread is another modification of the square thread, each side forming an angle of 141⁄2 degrees.
Giant Pumps in Placer Mines
PLACER mining of gold is carried on more or less extensively over the entire Pacific Coast.
There are a great number of rich placer deposits which cannot be reached by natural hydraulic heads, without incurring. very large expenses and immense labor. However, the successful and profitable working of these rich deposits may be undertaken by establishing a pumping plant and handling the water through giants as in gravity-pressure plants.
The idea is not a new one, but the question of the size and character of the pumping plant has never been determined in a satisfactory manner until very recently. The advent of the step-pressure pump for handling large quantities of water against high heads, operating at a high efficiency, has pointed out possibilities that could not be considered for any other class of pumps.
Step-pressure pumps have large capacity, are very much lighter than other pumps for a given capacity, are easily transported and installed, do not wear out like plunger pumps when handling
muddy water, will even handle water containing sand and small gravel without clogging or undue wear or great loss of capacity or of efficiency. The facility with which the pressure may be raised and lowered at the will of the operator, makes these pumps desirable factors in placer installations where pumping heads are required.
Very recently a placer plant using artificial pressure produced by one of these pumps, was installed for the United Iron Works, of San Francisco, Cal., at McCoy, Colorado. The deposit was adjacent to the Grand River in Eagle County, Col. It extended back on a sloping hillside for about 800 feet. The depth to bed rock was 12 to 30 feet. The material was assorted gravel and sand, including stones up to seven inches in diameter. The gold was very fine and associated with black sand. The best values were found on a clay stratum close to bed rock.
It was considered advisable to install the elevating plant on the lower side of the property; sluice the gravel down to the elevator; draw off the fines, and send them to a gold-saving station, discharging the tailings into Grand River.
The plant was of 100 miner's inch
capacity and was for testing purposes. The power equipment consisted of a 12 by 14-inch steam engine operating at 160 revolutions per minute and a 54-inch by 16-foot boiler, which under working conditions produced 65 horse-power. The pump took its water from the river 150 feet distant through an 8-inch pipe line and discharged into a 12-inch pipe line 200 feet long, which was split, sending part of the 100 miner's inches to the elevator, and part to the giant.
65 pounds per square inch, and the giant operator was able to throw a stream 233 feet horizontally, establishing a sluicerun 100 feet distant and carry waste into the river. The pump operated silently and without end thrust, and its performance was more than was expected. The fuel used was wood-pine and cedaronly two cords per day of ten hours being required.
Five men operated the entire plant. Five thousand pounds of refined concen
The elevator lifted 22 feet vertical, and required 60 miner's inches for its operation; and the balance was used to feed the same after the material had been sluiced close to the elevator. The sluice run was 24 inches wide, 16 inches deep, and set on a grade of 6 inches to 12 feet -twelve boxes, long riffled throughout. Near the lower end, an under-current was established, and the fines drawn off and sent to the gold-saving station.
When in operation, the water ran 4 inches in the sluice. The pump was a 7-inch of the two-step pressure type, having a capacity of 1,125 gallons per minute. It was speeded for 160 feet head, and operated at 850 revolutions per minute. The pump was set 10 feet above water-level, to avoid the high water of the spring season.
When pumping through the 24-inch tip on the giant, the gauge on discharge line near the pump showed a pressure of
trates were caught in 20 days' run, before operations had to cease owing to the severity of the weather.
It is worthy of note that the pressure was raised to 105 pounds per square inch
nearly to a head of 250 feet. It was found, however, that very little material advantage was gained. The conclusion was that the best results with fuel were to be had with more water and less pressure-just sufficient to loosen material in place. It was also noted that most gravels, even where packed and cemented to stand in vertical walls, would respond to pressure corresponding from 100 to 160 feet. The very successful operation of this plant, it is believed among old and experienced placer-mining men, will open up a great many very valuable deposits yet untouched. It promises to revolutionize placer mining in those regions where flowing water is not obtainable.