Document 7RZ3OR043je33JB8dgnXzx8aR

V American Society of Heating and Ventilating Engineers Guide, 1934 3. Connections to the chimney should be cleaned and in case of small boilers the pipe should be placed in a dry place after cleaning. 4. If there is much moisture in the boiler room, it is desirable to drain the boiler to prevent atmospheric condensation on the heating surfaces of the boiler when they are below the dew-point temperature. Due to the hazard of some one inadvertently building a fire in a dry boiler, however, it is safer to keep the boiler filled with water, A hot water system usually is left filled to the expansion, tank. , ^ 5. The grates and ashpit should be cleaned. .6. Clean and repack the gage glass if necessary. 7. Remove any rust or other deposit from exposed surfaces by scraping with a wire brush or sandpaper. After boiler is thoroughly cleaned, apply a coat of preservative paint where required to external parts normally painted. 8. Inspect all accessories of the boiler carefully to see that they are in good working order. In this connection, oil all door hinges, damper bearings and regulator parts. BOILER INSULATION Insulation for cast-iron boilers is of two general types: (1) plastic material or blocks wired on, cemented and covered with canvas or duck; and (2) blocks, sheets or plastic material covered with a metal jacket furnished by the boiler manufacturer. Self-contained steel firebox boilers usually are insulated with blocks, cement and canvas, or rock wool blankets; HRT boilers are brick set and do not require insulation beyond that provided in the setting. It is essential that the insulation on a boiler and adjacent piping be of non-combustible material as even slow-burning insulation constitutes a dangerous fire hazard in case of low water in the boiler. REFERENCES A.S.H.V.E. Code of Minimum Requirements for the Heating and Ventilation of Buildings. A.S.H.V.E. Standard and Short Form Heat Balance Codes for Testing Low-Pressure Steam Heating Solid Fuel Boilers (Codes 1 and 2). ' A.S.H.V.E. Performance Test Code for Steam Heating Solid Fuel Boilers (Code No. 3). A.S.H.V.E. Standard Code for Rating Steam Heating Solid Fuel Hand-Fired Boilers. Heating, Ventilating and Air Conditioning, by Harding and Willard, Revised Edition, 1932. A.S.M.E. Boiler Construction Code for Low Pressure Heating Boilers. Heating and Piping Contractors National Association Standards (boiler selection tables). House-Heating, published by American Gas Association. Handbook of Oil Burning, published by American Oil Burner Association. Heating and Ventilation, by Allen and Walker (3rd Edition). Selecting the Right Size Boiler, by Sabin Crocker (Heating, Piping and Air Con ditioning, February, March, April, 1932). . .. 346 Chapter 26 CHIMNEYS Natural Draft, Mechanical Draft, Characteristics of Natural Draft Chimneys, Determining Chimney Sizes, General Equation, Chimney Construction, Chimneys for Gas Heating DRAFT, in general, may be defined as the pressure difference between the atmospheric pressure and that at any part of an installation through which the gases flow. Since a pressure difference implies a head, draft then is a static force. While no element of motion is inferred, yet motion in the form' of circulation of gases throughout an entire boiler plant installation is the direct result of draft. This motion is due to the pressure difference, or unbalanced pressure, which compels the gases to flow. Draft is often classified into two kinds according to whether it is created thermally or artificially, viz, (1) natural or thermal draft, and (2) artificial or mechanical draft. Natural Draft Natural draft is the difference in pressure produced by the difference in weight between the relatively hot gases inside a natural draft chimney and an equivalent column of the cooler outside air, or atmosphere. Natural draft, in other words, is an unbalanced pressure produced thermally by a natural draft chimney as the pressure transformer and a temperature difference. The intensity of natural draft depends, for the most part, upon the height of the chimney above the graite bar level and also the temperature difference between the chimney gases and the atmosphere. A typical natural draft system consists essentially of a relatively tall chimney built of steel, brick or reinforced concrete, operating with therelatively hot gases which have passed through the boilers and accessories and from which all of the heat has not been extracted. Hot gases are an essential element in the operation of a natural draft system. A natural-draft chimney performs the two-fold service of assisting in the creation of draft by aspiration and. also of discharging the gases at an elevation sufficient to prevent them from becoming a nuisance. Natural draft is quite advantageous in installations where the total loss of draft due to resistances is relatively low and also in plants which have practically a constant load and whose boilers are seldom operated above their normal rating. Natural draft systems have been, and are still being, employed in the operation of large plants during the periods when the boilers are operated-only up to their normal rating. When the rate of operation is increased above their normal rating, some form of mechanical 347