Abstract:
A flue restrictor for installation in the flue piping of a heating system to reduce its effective cross sectional area comprises sheet metal inlet and outlet sections having flanges secured together in a joint that has a guideway in it for a sheet metal gate valve that may be transversely positioned to produce the desired cross-sectional area and riveted in place to provide a substantially tamper-proof assembly.

Description:
BRIEF SUMMARY OF THE INVENTION 
     It is the purpose of this invention to provide a device for controlling the draft in heating systems and, in particular, for reducing heat loss in many existing automatic heating systems using non-solid fuels, such as gas and liquified petroleum. 
     The invention accomplishes this purpose by means of a flue restrictor assembly that is adapted for retrofit, on-the-site installation in the flue piping of heating systems having excessive draft due to oversized chimneys and flue piping. This flue restrictor includes a housing that may be inserted in the flue piping to form a part thereof and a gate valve that is initially slidable in the housing so that the proper valve position for the desired draft control may be established, after which the valve may be locked to the housing to permanently set it in the desired position. 
    
    
     DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a diagrammatic side elevation of a forced air, gas fired furnace system for residential heating in which a flue restrictor embodying the invention has been installed, the arrows indicating the flow of air or combustion products; 
     FIG. 2 is a perspective view of the flue restrictor of the invention in operative condition but removed from a flue pipe; 
     FIG. 3 is a perspective-exploded view of the three main parts of the flue restrictor of FIG. 2 with the gate valve oriented for calibration; 
     FIG. 4 is an assembled view in perspective of the parts of FIG. 3; 
     FIG. 5 is a view similar to FIG. 4 but showing the gate valve in an optimum flow position ready for the calibration marking; 
     FIG. 6 is a perspective view of the marked gate valve removed from the flue restrictor housing and ready to be trimmed along the calibration marking; 
     FIG. 7 is a perspective view, partially exploded, showing the inverted, calibrated gate valve ready for insertion into the housing, it being understood that this operation is performed when the housing is installed in the flue piping and that the flue pipe sections are omitted to facilitate illustration; 
     FIG. 8 is an end elevation of the flue restrictor of FIG. 7 after the calibrated gate valve has been inserted and locked in permanent position; 
     FIG. 9 is a side elevation of the restrictor, broken away and partly in section, showing fasteners rotated into the plane of the drawing for securing the housing to sections of the flue piping; and 
     FIG. 10 is a side elevation of the restrictor of FIG. 8, partly broken away. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     A typical heating system 1 in which the invention may be used as illustrated in FIG. 1 and comprises a conventional heating appliance 3 connected by flue piping 5 to a chimney 7. The appliance 3 burns natural gas, propane, or liquified petroleum (i.e. non-solid fuel) and the system includes controls 9 to make its operation automatically responsive to heat demand. The heating appliance illustrated is a forced air, natural gas furnace for residential heating but the invention may be used with various other automatic gas or liquid fuel burning appliances such as warm air furnaces, steam or hot water boilers, hot water heaters, etc. 
     In accordance with the invention, a flue restrictor device 11 is installed in the flue piping 5 for the purpose of reducing the heat loss of the system through the piping 5 and chimney 7. Since the heating appliance is automatically operated, the restrictor 11 does not function to affect the rate of combustion or control the heat output of the system but provides a fixed orifice, calibrated to suit the system, which serves to control draft and limit the quantity of heated air drawn into the draft hood 13 during off and on cycles. 
     In the great majority of automatic gas or liquid fired heating appliances the rate of input of fuel is constant, so that it is possible and desirable to maintain a substantially constant draft from the chimney during operation. However, in heating systems installed prior to the recent shortage of natural gas and liquified petroleum fuels the chimneys have in general been oversized, in line with building and heating codes written with solid fuel (coal) installations in mind where strong drafts are needed. As a result, more draft is often provided than is needed for non-solid fuels. The result is that more air than necessary is drawn into the combustion chamber of both gas and oil heater appliances and heated room air is withdrawn by the chimney through the draft diverter on a gas-fired unit or the draft regulator on an oil-fired unit. To correct this condition, the flue restrictor 11 of the present invention may be installed on a retrofit basis in existing heating systems having excessive draft and locked in an adjusted position to fix the draft at substantially an optimum level for that particular system thereby reducing the system heat loss and conserving fuel. 
     Actual investigations have shown a substantial reduction in annual space heating fuel load due to use of suitable flue restriction. They have also shown that flue restriction may be used in combination with heating appliance derating (reduced burner orifice size to reduce fuel input and flame size) in order to obtain further savings. Similar results are believed to be obtainable with the particular structure of flue restrictor 11 described hereinafter. The restrictor 11 has the added advantage that it may be adjusted on the site to a selected setting that produces substantially optimum draft and vent conditions and then permanently secured or locked in that setting so that tampering to change it is extremely difficult. A further advantage is that its design enables it to be constructed of materials and to provide heat and flow conditions that minimize corrosion. An additional advantage is that it is of a relatively simple construction requiring a relatively simple calibration and assembly procedure and a minimum of tools and equipment for retrofit installation in the field. 
     The flue restrictor device 11 comprises three principal parts. They are inlet and outlet sections 15 and 17, which are secured together to form a housing 19, and a bladelike guillotine or gate valve 21. 
     The inlet section 15 has a tubular collar portion 23 of uniform diameter, circular cross section which terminates at its downstream end in an annular, radially extending, circular flange 25. The outlet section 17 has a tapered collar portion 27 of circular cross section which has, at its upstream end, an annular, radially extending, circular flange 29 corresponding to flange 25. The two flanges 25 and 29 are secured together in a substantially gas tight joint by welding, fast stitching, or any suitable fastening means as indicated at &#34;x&#34; in the drawings. This forms the housing 19 in which the inlet and outlet portions are coaxial and provide a straight through passage 31 for gas flow. Each section 15 and 17 is preferably of integral or one piece construction and formed of relatively thin sheet metal, preferably corrosion resisting, such as stainless steel. For example, the sections 15 and 17 may be made of 304 or 304L stainless steel, 0.018 inches thick. 
     The gate valve 21 fits in a guideway 33 in the joint between flanges 25 and 29 so that it may be projected into the passage 31. To provide optimum sealing, the guideway 33 is preferably formed entirely in the outlet or downstream section 17 and in its flange 29, as seen best in FIG. 3. It comprises an upset or offset portion in the flange 29 of a depth and width substantially equal to the thickness and width of the gate valve plate 21. The offset has a flat bottom 35 and straight, symmetrical, parallel sides 37 which, with flange 25, define slots 39 on the inner and outer surfaces of the housing 19 through which the flat gate valve is slidable in a radial direction with respect to the axis of the housing. The sides are tangent to the inner diameter of the housing so that the width of the guideway is substantially the same as the diameter of the passage 31. 
     The gate valve 21 has straight, parallel sides 41 which extend between the restrictor end 43 and the locking end 45 of the valve. The valve is of uniform thickness and its outside dimensions are symmetrical about both longitudinal and transverse axes lying on the plate. The valve ends 43 and 45 are preferably in the form of identical circular arcs having the same radius as the circular outer edge of flange 25. As shown in FIG. 4, the overall length of the valve 21 is preferably substantially less than that of passage 31 so that it cannot be used to completely close off the passage. The overall length is also preferably less than the width of the valve between the sides 41 to facilitate proper assembly. The width of the valve corresponds to the width of the guideway and is substantially the same as the inner diameter of the housing. 
     The restrictor or control end 43 of the gate 21 has a pair of angularly separated tabs 47 deformed from the plane thereof to extend at substantially right angles and provide stop means to limit insertion of the end 45 of the plate into the housing 19, as illustrated in FIG. 4. The lock end 45 of the gate 21 has a pair of angularly separated fastener receiving holes 49 extending through it which are intended to register with corresponding holes 51 in flange 25 and holes 53 in flange 29. Non-detachable fasteners, such as rivets 55, are preferably used to pass through openings 49, 51, and 53 and tightly and permanently secure or lock the gate valve 21 in a fixed position to housing 19, thereby making it extremely difficult to disassemble the restrictor 11 or change the position or setting of valve 21. The locking end 45 of the gate 21 also has a relatively large opening 57 through it, forming a port means for through flow of gas, which is located adjacent the bottom most part of the housing 19 when the device 11 is installed, as shown best in FIG. 8. 
     In use, the flue restrictor 11 is brought to the installation site in the condition of FIGS. 4 and 5 wherein the two sections 15 and 17 are joined together to form the housing 19 but the valve 21 is not yet locked in place, i.e., it is slidable in guideway 33. The installer first removes a section of flue piping 5 downstream from draft hood 13 and as close as feasible to chimney 7; and then inserts the housing 19 as a coupling in the place of the removed piping. The cylindrical inlet section 15 is telescoped on to the outside of the end of the adjacent upstream portion 59 of the flue and the tapered outlet section is telescoped inside of the end of the adjacent downstream portion 61 of the flue piping. The housing is adjusted so that the guideway is vertical. The two sections 15 and 17 are secured to the piping by suitable fasteners, such as sheet metal screws 63. Aligned sets of predrilled holes 65 in the sections 15 and 17 (shown only in FIGS. 2 and 10) may be provided to facilitate attachment of the housing to the flue piping 5. The combination of cylindrical upstream and tapered downstream sections telescoped on the outside and inside, respectively, of the adjacent flue piping facilitates installation and provides reasonable gas and air tightness at opposite ends of the unit 11. 
     The heating appliance 3 is started and operated for several minutes (or longer) until a normal, equilibrium condition for the heating system 1 is reached. Then the locking end 45 of the gate 21 is inserted into slot 39 and the valve is slidably moved upwardly in the guideway 33, the extent of upward movement being limited by engagement of tabs 47 with the outer edge of flange 25. The installer observes the effect of valve positioning on operation of the heating system and adjusts the valve vertically up and down until the desired draft and vent conditions are obtained. For example, he may determine when restriction causes spillage of combustion products into the room through draft hood 13 and then back off the valve a slight amount from that position. When he determines the proper valve position, he marks the restrictor end 43 (which is outside of the housing 19) by drawing an arc 67 on it along the outer edge of the flange 25 (FIGS. 5 and 6). The valve is then removed from the housing and cut to the required length. The gate valve 21 is preferably made of soft, trimmable metal, such as 0.033 inch thick aluminum, and metal snips or shears may be used to cut along line 67 and remove the outermost portion of restrictor end 43 containing the tabs 47. 
     The installer then inverts the gate valve, i.e., reverses it end for end, as shown in FIG. 7. He inserts restrictor end 43 into slot 39 and pushes the valve 21 upwardly until holes 49 register with holes 51 and 53 of flanges 25 and 29, at which position the edge of end 45 is flush with the outer edge of flange 25. He then inserts rivets 55, or other locking fasteners, secures them in place, and locks the gate valve 21 to the housing 19 so that it is permanently secured in the position of optimum adjustment as seen in FIG. 8. It is apparent that reversal of the valve 21, after cutting along line 67 and then locking the valve in place as in FIG. 8, will result in the edge 67&#39; of end 43 being in the same position in FIG. 8 as the edge of end 45 in FIG. 5, i.e., the position of optimum draft and vent restriction. The crescent shaped opening between the edge 67&#39; and the top of the housing 19 and the opening 57 provide an orifice means for passage 31 that increases the resistance to flow of flue products, thereby reducing the effective draft to the desired level. The result is less air drawn into the heating appliance, less air drawn into the draft hood, and less heat loss out the chimney. 
     In both FIG. 5 and FIG. 8 gas can flow through the opening 57. However, in FIG. 8, the permanent, locked, and operative condition, the hole is at the bottom of the housing where condensate or solids will collect. Gas flow through the hole will, therefore, tend to carry such condensate or solids down the flue and up the chimney. Since the condensate or deposited solids may contain corrosive materials this action serves to extend the life of the parts. The pattern of gas flow in combination with the thin gauge of the sheet metal parts of the restrictor 11 enable them to heat up rapidly to a temperature above the dew point of the gas passing through the flue piping and thus tend to minimize condensation. If the sections 15 and 17 are formed of stainless steel and the gate 21 of aluminum, as is preferred, the gate will corrode away before the sections and, in this event, the system 1 is simply returned to its flow and draft condition prior to retrofit installation of the restrictor 11. These materials also have the capability of withstanding the effect of long periods of shutdown in damp environments, such as exist in many basements in the summer. 
     The flue restrictor 11, therefore, provides a relatively simple, self-contained device for controlling the draft in the vent connection of a heating system and for reducing heat loss by retrofit installation in existing systems with excessive draft. Installation with simple equipment and parts and relatively simple instructions may be made on the site to suit the requirements of an individual heating appliance and system. When properly installed, the restrictor is permanently set and relatively tamperproof. The preferred design and construction of the restrictor 11 is such as to combat the effect of corrosive materials in the flue products. 
     Modifications may be made in the specific structure shown without departing from the spirit and scope of the invention. For example, instead of using the valve 21 itself as a calibration member a separate calibration plate (not shown) could be inserted into the guideway to obtain the desired draft and vent conditions and then used to mark the valve plate 21 for cutting the restrictor end of the plate 21 to the correct size for the desired draft.