Document ZJmBV6QR5m9ZprQoeq9Mb45o7

384 CHAPTER 18 1949 Guide cent reserve for igniting a new charge, more grate area may be required depending upon the depth of the fuel pot. Gas-Fired Boilers After determining the net load for the installation, gas designed boilers can usually be selected from manufacturers' tables of net load ratings which are based on piping and pickup allowances varying from 56 per cent for boilers of 200 sq ft and less to 35 per cent for boilers of 4000 sq ft and larger. If the piping and pickup load or other factors create an unusual load, a boiler should be selected which has an A.G.A. output rating equal to the maximum output required. Detailed recommendations for selection of gas designed boilers are given in the A.G.A. publication, Comfort Heating8. SPACE LIMITATIONS Boiler rooms should, if possible, be situated at a central point with respect to the building and should be designed for a maximum of natural light. The space in front of the boilers should be sufficient for firing, stok ing, ash removal and cleaning or renewal of flue tubes, and 'should be at least 3 ft greater than the length of the tubes. A space of at least 3 ft should be allowed on at least one side of every boiler for convenience of erection and for accessibility to the various damp ers, cleanouts, and trimmings. The space at the rear of the boiler should be ample for the chimney connection and for cleanouts. With large boilers the rear clearance should be at least 3 ft in width. The boiler room height should be sufficient for the location-of boiler accessories and for proper installation of piping. In general the ceiling height for small steam boilers should be at least 3 ft above the normal boiler water line. With vapor heating, especially, the height above the boiler water line is of vital importance. CONNECTIONS AND FITTINGS Steam outlet connections should be the full size of the manufacturers' tappings in order to keep the velocity of flow through the outlet reasonably low and to avoid fluctuation of the water line and undue entrainment of moisture, and should extend vertically to the maximum height available above the boiler. A steam velocity in boiler outlets not exceeding 25 to 30 fps at maximum load is recommended unless data are available to show that a higher velocity is satisfactory. Particular attention should be given to fitting connections to secure con formity with the ASME Boiler Construction Code for Low Pressure Heat ing Boilers. Attention is called in particular to pressure gage piping, water gage connections, and safety valve capacity. Where a return header is used on a cast-iron sectional boiler to distribute the returns to both rear tappings, it is advisable to provide full size plugged tees instead of elbows where the branch connections enter the return tap pings. This facilitates cleaning sludge from the bottom of the boiler sec tions through the large plugged openings. An equivalent cleanout plug should be provided in the case of a single return connection. Blow-off or drain connections should be made near the boiler and so arranged that the entire system may be drained of water by opening the drain cock. In the case of two or more boilers separate blow-off connec tions must be provided for each boiler on the boiler side of the stop valve on the main return connection. Water service connections must be .provided for. both steam and water Heating Boilers, Furnaces, Space Heaters 385 boilers, for refilling and for the addition of make-up water to boilers. This connection is usually of galvanized steel pipe, and is made to-the return main near the boiler or boilers. For further data on pipe connections for steam and, hot water heating . systems, see Chapter 23 and 24 and the ASME Boiler Construction Code for Low Pressure Heating Boilers. . Smoke Breeching and Chimney Connections. The breeching or smoke pipe from the boiler outlet to the chimney should be air-tight and as short and direct as possible, preference being given to long radius and 45-deg instead of 90-deg bends. The breeching entering a brick chimney should not project beyond the flue lining and where practicable it should be grouted from the inside of the chimney. A thimble, or sleeve usually is provided where the breeching enters a brick chimney. Where a battery of boilers is connected into a breeching each boiler should be provided with a tight damper. The breeching for a battery of boilers should not be reduced in size as it goes to the more remote boilers. Good connections made to a good chimney will usually result in a rapid response by the boilers to demands for heat. ERECTION, OPERATION, AND MAINTENANCE The directions of the boiler manufacturer should always.be read before the assembly or installation of any boiler is started, even though the con tractor may be familiar with the boiler. All joints requiring boiler putty or cement which cannot Be reached after assembly is complete must be finished as the assembly progresses. Five precautions that should be taken in all installations to prevent . damage to the boiler are: 1. There should be provided proper and convenient drainage connections for use if the boiler is not in operation during freezing weather. 2. Strains on the boiler due to movement of piping during expansion should be prevented by suitable anchoring of piping and by proper provision for pipe expansion and contraction. * 3. Direct impingement of too intense local heat upon any part of the boiler surface, as with oil burners, should be avoided by protecting the surface with firebrick or other refractory material. 4. Condensation in steam systems must flow back to the boiler as rapidly and uni formly as possible^ Return connections should prevent the water from backing out of the boiler. 5. Automatic boiler feeders and low water cut-off devices which shut off the source of heat if the water in the boiler falls below a safe level are recommended for mechanically fired.boilers. Boiler Troubles A complaint regarding boiler operation generally will be found to be due to one of the following: 1. The boiler fails to deliver enough heat. The cause of this condition-may be: (a) poor draft; (b) poor fuel; (c) inferior attention.or firing; (d) boiler too small; (e) im proper piping; (/) improper arrangement of sections; ig) heating surfaces covered with soot; (h) insufficient radiation installed; and (0 with mechanical firing, fuel burning equipment too small. 2. The water line is unsteady. The cause of this condition may be: (a) grease and dirt in boiler; (6) water column connected to a very active section and, therefore, not' showing actual water level in boiler; and (c) boiler operating at excessive rate of,out put. 3. Water disappears from gage glass. This may be caused by: (o) priming due to grease and dirt in boiler; (6) too great pressure difference between supply and return.