divide the product by 14,000. The quotient is the proper area of the safety valve in square inches. Example.-What is the proper diameter of the safety valve of a boiler that supplies an engine with steam, having a 64-inch cylinder, and with the piston travelling 220 feet per minute? Here 64 × 64 = 4,096, which multiplied by 220 = 901,120, and this divided by 14,000 64.3, which is the proper area of the safety valve in square inches. ANOTHER RULE FOR SAFETY VALVES. Multiply the nominal horse power of the engine by ·375, and to the product add 16.875. The sum is the proper area of the safety valve in square inches, when the boiler is low pressure. Example.-What is the proper diameter of the safety valve for a low pressure engine the nominal power of which is 140 horses? Here 140 × 375 = 52·5, adding to which the constant number 16.875, we get 69.375, which is the proper area of the safety valve in square inches for a low pressure engine. A 60-inch cylinder and 6-feet stroke is equal to 140 nominal horses power, so that this rule gives somewhat more than a square inch of area in the valve for each inch of diameter in the cylinder in that particular size of engine. The opening through the safety valve must be understood to be the effective opening clear of bridges or other obstacles, and the area to be computed is the area of the smallest diameter of the valve. Most safety valves are made with a chamfered edge, which edge constitutes the steam tight surface, and the effective area is what corresponds to the smaller diameter of the valve and not to the larger. All boilers should have an extra or additional safety valve of the same capacity as the other, which may act in case of accident to the first from getting jammed or otherwise. The dimensions of safety valve here computed is that adequate for letting off all the steam. But in some cases the whole steam is not supplied from one boiler, and a safety valve in such case must be put on each boiler, but of a less area, PROPER DIAMETER OF THE FEED PIPE. 221 in proportion to the smaller volume of steam it has to let off. If there are two boilers, the safety valve on each will be half the area of the foregoing; if three boilers, one-third of the area; if four boilers, one-fourth of the area; and so of all other proportions. The area of the waste steam pipe should be the same as that of the safety valve. TO FIND THE PROPER DIAMETER OF THE FEED PIPE. RULE.-Multiply the nominal horse power of the engine as com puted by the Admiralty rule by '04, to the product add 3; extract the square root of the sum. The result is the diameter of the feed pipe in inches. Example 1.-What is the proper diameter of the feed pipe in inches of an engine whose nominal horse power is 140? and 18.6 2.93 diameter of feed pipe in inches. = Example 2.-What is the proper diameter of the feed pipe I inches in the case of an engine whose nominal horse power 18 385? 385 nominal horse power of engine and 1/18.4 4.29 diameter of feed pipe in inches. TO FIND THE PROPER DIMENSIONS OF THE AIR PUMP AND CONDENSER. In land engines the diameter of the air pump is made half that of the cylinder, and the length of stroke half that of the cylinder, so that the capacity is 3th that of the cylinder; and the condenser is made of the same capacity. But in marine engines the diameter of the air pump is made 6 of the diameter of the cylinder, and the length of the stroke is made from 57 to 6 times the stroke of the cylinder, and the condenser is made at least as large. In some cases the air pump is now made double-acting, in which case its capacity need only be half as great as when made single-acting. TO FIND THE PROPER AREA OF THE INJECTION PIPE. RULE.-Multiply the nominal horse power of the engine, as computed by the Admiralty rule, by 0.69, and to the product add 2.81. The sum is the proper area of the injection pipe in square inches. Example 1.-What is the proper area of the injection pipe in square inches of an engine whose nominal horse power is 140? 140 = nominal horse power of engine Answer 12.47 area of injection pipe in square inches. Example 2.-What is the proper area of the injection pipe in square inches of an engine whose nominal horse power is 385? 385 26.56 nominal horse power of engine constant multiplier 2.81 constant to be added Answer 29.37 area of injection pipe in square inches PROPER AREA OF THE FOOT VALVE PASSAGE. 223 The area of the injection orifice is usually made about 1-250th part of the area of the piston, which, in an engine of 385 horse power, would be about 27.7 inches of area. For warm climates the area should be increased. TO FIND THE PROPER AREA OF THE FOOT VALVE PASSAGE, RULE. -Multiply the nominal horse power of the engine by 9, divide the product by 5, add 8 to the quotient. The sum is the proper area of foot valve passage in square inches. Example 1.-What is the proper area of the foot valve passage in square inches of an engine whose nominal horse power is 140? 140 9 nominal horse power of engine constant divisor 5)1260 252 Answer 8 constant to be added 260= area of foot valve passage in square inches. Example 2.-What is the area of foot valve passage in square nches of an engine whose nominal horse power is 385? The discharge valve passage is made of the same size as the 100t valve passage. A common rule for the area of the foot and discharge valve passages is one-fourth of the area of the air pump, and the waste water pipe is made one-fourth of the diameter of the cylinder, which gives a somewhat less area than that through the foot and discharge valve passages. Such rules, however, are only applicable to slow-going engines. In rapid-working engines, such as those employed for driving the screw propeller by direct action, and in which the air-pump is usually double acting, the area through the foot and discharge valves should be equal to the area of the air-pump, and the waste water pipe should also have the same area. In all cases, therefore, in which these or other rules dependent on the nominal power are applied to fast-going engines, the nominal power must be computed by the Admiralty rule, in which the speed of the piston is taken into account. TO FIND THE PROPER DIAMETER OF THE WASTE WATER PIPE. RULE.-Multiply the square root of the nominal horse power of the engine by 1.2. The product is the diameter of the waste water pipe in inches. Example 1.-What is the diameter of the waste water pipe, in inches, of an engine whose nominal horse power is 140? 140 nominal horse power of engine and 140 = 11.83 1.2 = constant multiplier Answer 14:19 diameter of waste water pipe in inches. Example 2.-What is the diameter of waste water pipe, in inches, of an engine whose nominal horse power is 385? Answer 23.54 diameter of waste water pipe in inches. CAPACITY OF THE FEED PUMP. The relative volumes of steam and water are at 15 lbs. on the square inch, or the atmospheric pressure, 1,669 to 1; at 30 lbs., or |