March 17, 1916. THE COLLIERY GUARDIAN. 519 SAFETY CATCHES ON THE CAGE. By Noah T. Williams. In order to arrest the cage in the shaft in the event of a breakage of the winding rope or attachment, various designs of safety catches have been brought out in this and mining countries during the last 50 years. These accidents may be caused by defects in the rope or connections, deranged guides or a broken head-gear pulley. Under present-day conditions, many shafts are of great depth, and this in turn necessitates large batches of men to be transported in and out of the mine. It therefore becomes a matter of prime importance to provide, where applicable, a safety appliance which will prevent risk to life and damage to the shaft when a rope or tackle breaks,-inasmuch as absolute security against breakages can never be attained, in spite of daily inspection and the utmost care on the part of the management. On these grounds the question deserves the consideration of all colliery owners. The problem is extremely difficult to solve, especially for heavy cages running on iron or wire rope guides and moving at high velocities. xO. si 1 fl 1 A - CLIP B - CONTROL SHAFT C - CLIP FORKS D - WEDGE E - ADJUSTABLE CONNECTING ROD F - SELF-ACTING WEIGHT G - AUTOMATIC SUSTAINING LEVER&5PRING J - CONTROL GEAR K - CONTROL CHAIN L - CAGE SHOES M - GUIDE ROPES Safety catches are more extensively, used on the Continent than in this country, where wooden guides are more in general use. The safety appliances are of two kinds :—(a) Those which cause a sudden stop of the cage by their locking action at the instant -the rope breaks; (b) those which set up a frictional resistance sufficient, not only to destroy the momentum of the cage, but also to counteract the acceleration due to the force of gravity, and finally bringing the falling cage to rest. For a heavy and high-speed cage, it must bo admitted, however, that the latter system possesses advantages in point of safety over the former, inasmuch as a- sudden stop would generate such enormous shocks as would cause a breakage of the locking parts or guides. It makes considerable difference whether the break occurs in the ascending or descending rope. The danger of the rope breaking is‘ obviously greater when the cage is ascending, on account of the greater load. In the case of the ascending load, the moving mass travels upwards with a velocity = V feet per. second at the instant a breakage occurs, and, like a body thrown into the air, it will reach a height equal to (the resistance -of the rope guides being left out of consideration). After covering this distance, the mass is for a moment at rest, and when the safety catch is thrown into action it will only have to resist the weight of the eage, which load it may easily be designed to withstand. On the. other hand, if the descending rope should break, it is evident that, even when the catch is immediately thrown into gear, a shock is caused by the moving cage equal to W V2 - where W is the weight of the cage. If the arrest of the cage is effected in a certain interval of time, t, then the additional work to bo performed by the catch would be represented by Wfe, where h is the distance traversed after breakage. It is clear from the foregoing that the danger from a breakage is increased by a slow-acting catch, and that a catch of whatever type is adopted has the best chance of. acting successfully with the ascending rope; but if a catch is effective solely in the case of the ascending cage, the risk of damage has been reduced to. one-half. Cases are on record of safety catches coming into opera- tion during the. ordinary running of the cages, without the rope having broken. This failure is often attributed to lack of careful adjustment and overhauling of the appliance and state of the guides by the man whose duty it.should be. to ensure perfect working order, Catches should be fitted with reliable springs, and they, require, careful adjust- ment so that they will neither catch on quick winding nor fail to act when required; moreover, the elasticity of 'springs does not remain permanent, and shaft water will rapidly deteriorate them unless they are frequently oiled. The fundamental principle of safety catches can be gathered from a brief description and illustration of the appliance devised by the Providence Safety Clip Company Limited. This type is installed at many collieries and is considered very satisfactory. When the rope is taut, the control chain K is held in tension and the serrated catches A are free from the guides. In the event of the rope breaking, the pull on the chain K is relieved, and the serrated catches A, through the action of the lever and spring G, press against the guides. The final locking, however, takes place gradually, as the ends of the clip forks advance over the wedge-shaped block D, and is independent of the . action of the spring. It may be noted that the heavier the cage, the greater becomes the grip. The self-acting weight F keeps the springs at a proper tension, thus preventing the catch from coming into action when , the rope..tension on. the .descending cage is reduced through, swaying and increasing velocity. In ease of the ascending rope breaking, the gear immedi- ately sustains the cage on the turning point, thereby preventing shocks. After the rope breaks, the cage can be released by merely lifting it. THE PRESSURE OF GAS IN COAL BEDS.* By N. H. Barton. (Continued from page 120.) Volume of Gas from Holes in Solid Coal. Petit also made some tests to determine the volumes of gas given off by holes bored into solid coal in connec- tion with his pressure tests at St. Etienne. He bored many holes 3 to 23 ft, deep, and fitted them with iron pipes securely tamped in such position as to leave 3-164 sq. ft. of coal exposed at the bottom of the hole. In general the pressure and volume of gas increased with depth. Although the larger volumes of gas came with the higher pressures, the relation of pressure, to volume was by no means uniform. In two holes of the same depth the gas had about 9 lb. pressure in each, but one gave off twice as much gas as the other. In 23 ft. holes in stalls, with pressure averaging not quite lib. to the sq. in., the volume of gas was nearly 0-09 cu. ft. per minute; with mean pressures of 31b., it was nearly 0-1 ft.; and with pressures of 8 lb,, 0-23 cu. ft. In 23 ft. holes in headings with a pressure of 7 lb. to the sq. in., the volume of gas was 0-06 cu. ft.; with a pressure of 9-3 lb., 0-1 cu. ft.; and with high pressures, such as 20 lb., 0-28 cu. ft. per minute. In Simon’s determination of pressures in solid coal.at Lievin, measurements were made of the volume of gas given off in holes 30 to 39 ft. deep. One hole,, contain- ing about 13 ft. of tamping, and an exposed coal area of about 16 sq.ft., gave off 7| cu. ft. of gas in the first 20 seconds. The volume decreased to about -j cu. ft. an hour. Three days later, when the pressure was 421b., gas was given off at a rate of 4| cu. ft. in the first 20 seconds after the cock had been opened, and then the' average volume decreased to about L cu, ft. an hour, a moderate amount. The volume of gas from a, given pressure was in proportion to the vacant space at the bottom of the hole. In tests in another bed of coal (Alfred) one hole, with only 1J sq. ft. of coal exposed at the bottom, gave off 0-35 cu. ft. of gas a minute, a rela- tive volume 50 times greater than given by the hole in the previous test, the area of coal exposed being con- sidered. Wood, in conducting his determinations of gas pres- sures in tire solid coal in English mines, measured the volumes of gas given off by some of the holes. Each pipe was set so as to leave a tubular chamber at the end of the hole. Unfortunately, the chambers varied in size from 1£ in. to 3 in. in diameter, and from 2 ft. to 6 ft. in length, so that the coal surface exposed varied from 95 to 570 sq. in. The gas emanations varied from 0-6 to 15-72 cu. ft. an hour, or from 0’3 to nearly 6 cu. ft. to each square foot of coal exposed. The results were as follow :—Eppleton, 6-1 to 15'7 cu. ft. per hour, or 1-1 to 6-0 cu. ft. per square inch maximum, pressure 2041b. to 2351b.; Boldon, 0’6 to 10’3 cu.ft. per hour, or 0'3 to 3-9 cu. ft. per square inch, pressure 1791b. to 461 lb.; Harton, 2-40 to 3-52 cu. ft. per hour, or 0-4 to 1'4 cu. ft, per square inch, pressure 197 lb. to 295 lb. In most cases the minimum amount of gas given off was about half as much as the maximum. In the Boldon holes the maximum volume was not attained until the measurements had continued for some time, whereas in the others it was quickly attained. The maximum pres- sure was developed prior to the time of maximum gas emanation. Barometric observations made throughout showed no relation of barometric pressure either to volume or pressure of gas. In No. 3 hole at Eppleton volume observations were made for three weeks, the volume determined varying from 11-40 eu. ft. per hour at the outset to 6-86 cu. ft. at the end of the test. Effect of Rock and Water Pressure on Gas Pressure in Coal. The gas in coal bears the pressure of the overlying strata, so far as that pressure tends to compress the pores holding the gas. Another important factor is the pressure of water in the overlying strata. It is a well- established fact that all rocks of the upper few thousand feet of the earth’s crust contain more or less water in their pores, and this ordinarily constitutes a water column extending up to the ground water level of the district. There are no ‘ ‘impermeable” rocks, although the texture of glassy-lavas and of-some compact crystalline rocks is so fine as greatly to impede water movement except where the rocks are fissured. Clays and shales permit little water movement, but underground their pores are usually saturated with water. So-called “bone-dry”, boreholes and mine workings yield materials that contain considerable interstitial moisture when tested in the laboratory. The coal measures consist largely of alternations of sandstone and clays or shales containing considerable water that is much in evidence in some mines, and coal itself contains from 1 to 10 per cent, of water (air-drying loss). This water, when it fills the pores and crevices of the coal and extends to the surface, constitutes a column which, in a mine 1,000 ft. deep, has a pressure of 435 lb. to the square inch. This pressure is not manifested directly in a mine, for it is largely sustained by friction, capillarity, or slowness of delivery from the less permeable beds. Although the water may not be sufficiently mobile to penetrate into all the pores in coal containing gas, its pressure must bear on many of them. In a mine, part of the water pressure is relieved by the flow of water from various outlets, but the pressure is often manifested to the amount of many pounds to the square inch when a large water-bearing fissure is encountered. Draining the strata by pumping and mining diminishes the water pressure, but the practical effect of such relief as a factor -in gas emanation has not been ascertained. * From Bulletin 72 of the U.S.A. Department of the Interior,. Bureau of Mines.