Abstract: The present invention is a method and apparatus for controlling the flow of combustion air and/or combustion products through a furnace which may experience changing flow restrictions. The method provides constant flow through an induced-draft furnace by determining torque values applied to an inducer motor of the furnace from a lookup table, which is established by operating a test furnace under changing flow restrictions, typically by measuring furnace flue gas carbon monoxide concentration. A lookup table according to the invention may include motor operating performance plots for controlling inducer speed under operating conditions, and threshold plots, which may be employed for determining activation of furnace events such as ignition, gas valve energizing, and shutdown. In an adaptive method of the invention, an adaptive lookup table is provided by averaging torque values from each of several lookup tables.

Abstract: A control system for regulating a flow rate of a heat transfer fluid in a heat transfer system, the heat transfer system having a heat transfer fluid flow path, flow control device for creating flow along the path, a fuel source for providing a combustible fuel to the path, an air source for providing combustion air to the path, and an assembly for combusting the fuel and air, the control system comprising a sensor for sensing a measured flow value at the air source, a controller for storing an optimum flow value at the air source and for storing a range of operating control values for the flow control device, the operating control values corresponding to the optimum flow value, a system for calculating a deviation between the measured flow value and the optimum flow value, and a system for varying the operation of the flow control means in accordance with deviation.

Abstract: A gas-fired, simulated log fireplace insert incorporating an automatic flue damper for controlling the operational state of a chimney vent (open/closed) in response to gas combustion, an externally mounted carbon monoxide detector for terminating or inhibiting gas combustion in response to an unsafe level of detected carbon monoxide and a temperature actuated switch, disposed within the firebox area of the fireplace proximate the flue, for terminating gas combustion in response to excessive fireplace temperatures caused by a malfunctioning damper.

Abstract: A gas-fired, simulated log fireplace insert incorporating an automatic flue damper for controlling the operational state of a chimney vent (open/closed) in response to gas combustion, an externally mounted carbon monoxide detector for terminating or inhibiting gas combustion in response to an unsafe level of detected carbon monoxide and a temperature actuated switch, disposed within the firebox area of the fireplace proximate the flue, for terminating gas combustion in response to excessive fireplace temperatures caused by a malfunctioning damper.

Abstract: The present invention relates to an intelligent transient eliminator which allows a gas ignition system to prevent gas valves from being turned off by a pressure switch in response to a transient pressure wave. The transient eliminator is preferably provided in a HVAC unit or furnace which burns a fuel such as natural gas. An ignition control system employing an intelligent transient eliminator provides a secondary relay across the pressure switch. The secondary relay is controlled by a signal to an ignitor in the furnace. The secondary switch is tested before energizing the inducer blower in the system.

Abstract: A heat activated flue damper actuator employing an assembly of shape memory alloy springs with linkages to a conventionally designed contemporary flue damper. The combination of the spring material, spring configuration and dimensions, linkage/fastening scheme to the flue damper shaft and placement in the water heater's heating chamber are all controlled to optimize the energy efficiency of a conventionally designed, pilot-lit or pilotless ignition, contemporary gas water heater.

Abstract: A heat activated flue damper actuator employing an assembly of shape memory alloy springs with linkages to a conventionally designed contemporary flue damper. The combination of the spring material, spring configuration and dimensions, linkage/fastening scheme to the flue damper shaft and placement in the water heater's heating chamber are all controlled to optimize the energy efficiency of a conventionally designed, pilot-lit or pilotless ignition, contemporary gas water heater.

Abstract: An actuator employing a unidirectional electric motor driving a first rotating member connected to a second rotating member through a pivotable link of which a first end is connected to the first rotating member at a smaller distance from its axis of rotation than the distance between the point at which the second end is connected to the second rotating member and its axis of rotation. An enegerization circuit includes first and second limit switches through which the motor is alternately energized to rotate the second men%her in opposite directions to first and second limiting positions respectively.

Abstract: A pilot pressure switch for a furnace detects the fluid pressure within the pilot line for a pilot flame, and upon the fluid pressure in the pilot line exceeding a predetermined value, an electrical signal from a thermostat may be passed to a furnace blower control to operate the furnace main blower and furnace vent blower.

Abstract: A method and apparatus for applying exhaust gas analysis to simple combustion control systems wherein the fuel flow and air flow control devices are interconnected with fixed mechanical linkage, or interconnected by a single specific signal, between the fuel flow and air flow control devices. An apparatus and method are disclosed to automatically compensate the air-to-fuel ratio, pre-calibrated on a volume basis, for uncontrolled variations of air or fuel quality such as density, BTU content and the like so that the calibration of the rate of combustion air flow relative to the rate of fuel flow will always be substantially correct even while these flow rates are changing.

Abstract: A stack damper control apparatus for positioning a stack damper and controlling a fuel source in response to closing of a temperature sensitive switch. Limit switches comprising drop cams are coupled to the drive shaft of the damper. In response to a call for heat, a motor turns the damper, coupling a source of energy to a fuel source when the damper is open and the limit switches transfer. A relay coil is energized to hold open a switch providing a parallel energization path for the motor. When the call for heat has been met and the temperature sensitive switch opens, the relay de-energizes closing the parallel energizing path and allowing the motor to close the damper. Provision is made for a safety interlock to ensure the fuel source is not activated when the damper is closed. Provision is also made for interface to a blocked vent shutoff system.

Abstract: A coffee bean roasting device for roasting coffee beans by applying hot air to the coffee beans. The coffee bean roasting device includes a detector for detecting a factor exerting influence upon the roasting state of coffee beans, and a controller for controlling the hot air supplier and/or exhaust discharger in accordance with a detection signal input from the discharger. The controller may be, for example, an electronic control portion such as computer including a pressure sensor for detecting a pressure value of the roasting space as a factor exerting influence upon the roasting state of coffee beans and adapted to record a pressure value input from the pressure sensor in a particular roasting state of coffee beans as a particular pressure value and control the exhaust discharger to regulate the amount of exhaust gas on a basis of the pressure value input from the pressure sensor, such that the pressure value of the roasting space becomes such recorded particular pressure value as a target value.

Abstract: A method of controlling the pressure in an incinerator for incinerating municipal refuse, industrial waste, etc. Exhaust gas from an incinerator typically passes through an exhaust gas cooler and an exhaust gas treating device and then discharged into the atmosphere by the action of an induced draft fan. In a method of controlling the pressure in such an incinerator for incinerating municipal refuse, industrial waste, etc. gas, e.g., part of the flow of exhaust gas induced by the induced draft fan or air taken in from the atmosphere, is added to a gas flow path upstream of the inlet of the induced draft fan through an addition gas line provided with an addition gas control damper. The addition gas control damper is controlled on the basis of an output from a furnace pressure controller such that when the furnace pressure is relatively high, the flow rate of the addition gas is reduced, whereas, when the furnace pressure is relatively low, the flow rate of the addition gas is increased.

Abstract: A HVAC system (10) employs a gas valve (20) to supply gas for combustion within a heating portion (12) of the system. An exhaust (22) removes combustion products using a motor (28) driven exhaust fan (24). An apparatus (34) controls combustion and uses a sensor (36) for sensing the rotational speed of a motor shaft (26). A switch (T1) is responsive to sensed motor speed to open and close the valve, the valve being opened only if the motor is operating within a predetermined speed range. A first speed discriminator (48A) enables of the switch to open the valve when the motor speed exceeds a first predetermined value. A second speed discriminator (48B) disables the switch to close the valve when motor speed exceeds a second and higher predetermined speed which is indicative of a blocked exhaust, or a fan blade is loose. This latter action insures that a build-up of potentially dangerous exhaust gases cannot occur.

Abstract: The present invention provides a water heater capable of exhausting flue gases from an interior space of a building to an exterior space and is adapted for installation through an upstanding wall. The water heater has an insulated tank with a water inlet and a water outlet together with a flue pipe opening at one end thereof beneath the tank upon a combustion chamber containing a fuel burner. The other end of the flue pipe opens at the top of the tank upon a flue gas collector and has a flue gas restricter for restricting the outward flow of flue gases from the flue pipe. The collector includes a collector box connected to the top of the water heater above and in alignment with the flue pipe, a blower and a low temperature flue gas exhaust line. The collector box has at least one air inlet for mixing air from the interior space of the building with flue gases exiting the flue pipe to inhibit condensation and reduce the temperature of the flue gases flowing through the exhaust line.

Abstract: A control system for a gas fired, direct ignition, induced draft furnace includes a radiant heat sensing switch responsive to a hot surface igniter and burner flame, a single-pole, double-throw pressure switch responsive to fluid flow effected by the inducer, and a plurality of relays responsive to the radiant heat sensing switch, the pressure switch, and various other connected switching means.

Abstract: A fuel-fired, forced draft heating appliance includes a draft inducer fan having an inlet connected to a vent hood, an outlet connectable to a vent pipe, and an interior housing region in which a negative pressure is generated during normal appliance operation. The vent hood receives hot combustion gases generated by the appliance, and has an inlet for receiving ambient dilution air that mixes with and cools the combustion gases entering the hood and subsequently discharged into the vent pipe by the fan. A combination pressure and temperature limit control is used to sense the presence of an obstruction in either the vent pipe or the vent hood inlet and responsively shut down the appliance. The control includes a vacuum switch external to the fan, a bimetallic disc-type temperature sensor disposed within the negative pressure fan region, and a conduit interconnecting the switch and the temperature sensor.

Abstract: A flue gas closure system for a furnace which includes a burner and a heat exchanger through which flue gas flows. The system includes a closure member which in an open position permits the flow of flue gas through the heat exchanger and in a closed position prevents the flow of air through the heat exchanger and means for causing said closure member to be in an open position when the burners are on and to be in a closed position when the burners are off. The closure member includes a closure plate which is slidably connected to the heat exchanger. An actuator is connected to said closure member for moving said closure member to at least one of the open and closed positions.

Abstract: The present invention relates generally to pulse combustion furnaces, and more particularly to an improved air flapper valve assembly for use in association therewith, such improved air flapper valve assembly having a valve body formed from an elastomeric material which results in significant reduction in air valve sound and vibration.

Abstract: An exhaust fan blower is provided for use in induced draft furnaces. An integrally molded fan housing and exhaust conduit is provided of a material impervious to the corrosive effects of exhaust gas condensates. The conduit is of a round cross section to mate with an associated flue pipe. The fan blower includes a conduit in communication with a pilot light for constantly venting the pilot light irrespective of operation of the blower. A first bore in the fan blower housing provides means for monitoring the vacuum developed therein, while another bore provides a means for thermally sensing a blocked or restricted flue condition. A flange and mounting lugs about the periphery of the fan blower housing provide a means for mounting the system to the side of a furnace panel, while sealing such mounting engagement. A motor mounting bracket for the fan blower serves as a cooling fan guard and heat sink, having a bearing contact mounting seat cast integrally to the bracket.

Abstract: The present invention involves a two stage furnace and a method of controlling the fans. In the furnace, a high pressure switch indicates whether sufficient air is present to support high combustion. Normally the furnace operates at one of the combustion settings. The circulator fan operates at the high speed setting when the high pressure switch indicates that sufficient air is present for high combustion, and operates at the low speed setting when the high pressure switch indicates that insufficient air is present for high combustion.

Abstract: In an inducted draft, fuel-fired furnace a flow restriction in the external exhaust flue is detected, and the furnace burners responsively deactivated, by a thermal sensing switch mounted in a spaced relationship with a small flow opening formed in a sensor housing externally secured to the inducer fan outlet section over a wall opening therein. During normal burner combustion product discharge flow through the exhaust flue, a small vane within the inducer fan outlet section creates a venturi therein which draws ambient air within the furnace housing across the temperature sensing switch and into the fan outlet section through the sensor housing opening. The temperature of this ambient air is below the switch set point so that continued burner operation is permitted.

Abstract: Electronic control system for a gas-fired/hot air furnace includes a primary control unit which controls the flow of fuel to the furnace. The furnace has heating and cooling space thermostats and a comfort fan to supply heated or cooled air to the space being monitored by the thermostats and an induced draft blower which supplies combustion air into the furnace for heating. A first switch and associated relay drive selectively energizes the comfort fan for low speed heating operation and a second relay switch and associated relay drive selectively energizes the comfort fan for high speed cooling operation. Actuation of the heating thermostat energizes a third switch and associated relay drive which energizes the induced draft blower. A high temperature thermostat located to sense excessive furnace temperatures is also connected to actuate the third relay to energize the induced draft blower in an excessive temperature condition.

Abstract: A microprocessor control determines, in the course of initiating a heating cycle, whether the blower is operating in the continuous mode, and if it is, the control prompts the blower to be turned off prior to the ignitor being turned on. In this way, the blower and ignitor are never on at the same time and the instantaneous total current draw is limited to thereby reduce the occurrence of burned out fuses or circuit breaker trips.

Abstract: Damper position of a damper in a heating system is monitored. The damper is movable between end positions in response to movement of a motor shaft. The motor shaft moves in response to a movement request signal. A shaft position signal is received by a position detector and has a value representative of position of the motor shaft. When the damper reaches an end position, it is determined whether the value of the shaft position signal is within a predetermined tolerance. If it is outside of the tolerance, then the system is shut down as unreliable; otherwise, the shaft position signal is recalibrated to maintain accuracy.

Abstract: The present invention includes an exhaust fan for exhausting combustion gases from a gas fired water heater, a gas pressure diaphragm switch for operating the exhaust fan in response to fuel flowing to the burner of the water heater, and a safety device for preventing fuel flow to the burner upon detecting undesirable changes in combustion gases. The apparatus further includes a time delay to continue operation of the exhaust fan and exhaust residual combustion gases for a short time after fuel flow to the burner has ceased. In one form the time delay is a time delay relay switch and in another form it is a flow restricting orifice that restricts the flow of fuel from the gas pressure diaphragm switch, thereby maintaining a closed circuit to the exhaust fan.

Abstract: Provision is made for sensing when the gas valve relay contacts are welded, or stuck, in the closed position and for responsively turning off the inducer motor when that occurs. This in turn causes the pressure switch to open to thereby cut off the power to the gas valve and cause it to move to the closed position.

Abstract: A method of and apparatus for automatic flue damper control of a solid fuel burning stove has a driveshaft connected to the damper, a plurality of cams on the driveshaft, a plurality of thermoswitches on the chimney pipe, a plurality of selection switches operated by the cams, and an electric motor controlled by the thermoswitches and the selector switches for moving the damper to open, partial and closed positions in response to low, rising, and too high temperatures respectively.

Abstract: An integrated electronic control arrangement is disclosed in the illustrative environment of burner such as in a gas-fired furnace. The control incorporates a self-test feature which shuts down the furnace in the event of any one of a number of possible sensed faults. Self-testing occurs automatically before an attempt at ignition and during furnace operation. Proper functioning of the sensor which senses for induced air flow through the burner combustion chamber is tested prior to enabling a fan which causes that induced air flow. Air flow is confirmed by sending to and receiving back from the sensor a sequence of pulses. Should air flow not be sensed during a combustion period, combustion is terminated. A flame sensor is provided for determining the presence of a flame in the combustion chamber. During times when a flame should be present, pulse sequences are sent to and received back from the flame sensor to confirm that a flame is present.

Abstract: A catalytic bed has an upright forward surface openly exposed to the living space and generates a partially laminar flow and a partially turbulent flow of substantially smokeless gaseous combustion products upward along the bed surface, with laminar flow adjacent thereto and the turbulent flow positioned forward thereof. A collection chamber is positioned above the bed and has spaced apart lower and upper walls to define a rearward collection chamber and a forward inlet space. A negative pressure source is connected to the collection space to create an exhaust flow therefrom. A baffle wall extends laterally and projects upwardly from the lower wall toward the upper wall, terminating at a distance therefrom to create a pressure drop between the collection and inlet spaces sufficient to provide a substantially uniform draw along the length of the baffle wall.

Abstract: An improved power vent and associated control system for a heating apparatus such as a furnace. The invention utilizes a vent blower and a flow control orifice device permitting the use of a single size air moving device and motor with different size furnaces. The control is arranged to discontinue delivery of fuel to the furnace in the event of a blockage of the furnace flue or a failure of the air moving structure. In one form of the invention, a pressure condition is sensed downstream of the air moving structure to detect the failure conditions. In another form of the invention, the control utilizes structure to sense the speed of the air moving device. The invention comprehends the use of a motor for driving the air moving device which varies in speed substantially between the unloaded and loaded conditions. The air moving device preferably unloads under high discharge pressure conditions, such as by a blocked flue.

Abstract: A method and apparatus for stimulating a subsurface, oil-bearing reservoir, in which a fuel is burned in the presence of a combustion-supporting gas to produce an essentially uncontaminated flue gas at a pressure significantly above the reservoir pressure, water is intimately mixed with the flue gas, the water is vaporized to produce a mixture of flue gas and steam and the operating parameters of the water vaporization and, particularly, the fuel combustion are controlled by passing the mixture of flue gas and steam through an iris-type shutter having a variable diameter opening and varying the diameter of the variable diameter opening.

Abstract: An emergency heat bypass arrangement for a furnace in which the normal controller path is supplemented by an alternate path through a relay subject to an emergency heat switch controlling the solenoid of the relay, and the relay includes additional contacts for keeping power on the solenoid even after the furnace high pressure switch changes contacts to provide heating when said controller has malfunctioned.

Abstract: A gas burner control system for controlling operation of a furnace having a blower fluidically connected to the combustion chamber of the furnace utilizes a mass flow sensor for preventing or discontinuing burner operation in the event of a blower failure or a predetermined degree of blockage in the fluid flow path controlled by the blower. The mass flow sensor includes circuit means which enables use of unmatched sensors, enables establishing of a desired value of temperature difference between sensors, enables establishing a temperature difference that is not constant so as to compensate for different ambient air densities, and enables compensating for voltage variations at different ambient air temperatures.

Abstract: A housing supporting a signal-controlled, power operating unit for a damper is mounted internally within a duct by a tubular supporting sleeve in an angularly and axially adjusted position projecting from an open end of the duct. A shield fixed to the external end of the sleeve backs an annular sealing flange engaged by the damper element, which is enclosed by a flow deflecting hood slidably assembled on the shield.

Abstract: Disclosed is a heating system having a combustion air blower, a fuel valve for providing fuel to a burner, and an exhaust stack for exhausting combustion products. Also disclosed is flow sensor apparatus operatively associated with the stack for providing control signals to a furnace control, the control signals being related to flow conditions in the stack.

Abstract: A movable wick type oil stove which comprises a wick for absorbing oil to provide a fire at the top of the wick, wick cylinders defining a space for disposing the wick therein means for moving the wick in the vertical direction along the wick cylinders, and a deodorizing device for absorbing or removing gas causing an undesirable smell and produced when the fire at the top of the wick is extinguished by lowering the wick to a predetermined position. The deodorizing device comprises a suction device, a movement-sensing element for sensing the movement of the wick, and a temperature-sensing element for sensing a temperature around the wick.

Abstract: A movable wick type oil stove which comprises a wick for absorbing oil to provide a fire at the top of the wick, wick cylinders defining a space for disposing the wick therein means for moving the wick in the vertical direction along the wick cylinders, and a deodorizing device for absorbing or removing gas causing an undesirable smell and produced when the fire at the top of the wick is extinguished by lowering the wick to a predetermined position. The deodorizing device comprises a suction device, a movement-sensing element for sensing the movement of the wick, and a temperature-sensing element for sensing a temperature around the wick.

Abstract: The present invention is an electronically controlled, automatically operated flue damper mechanism which is totally fail safe in operation. The mechanism is to be fitted within the draft hood of a thermostatically controlled heating device such as a gas or oil fired furnace. The electronic control circuitry of the damper being integrated with that of the heating device to which it is fitted. The action of the damper being to close the flue a sufficient time after combustion has stopped, to allow all noxious gases from combustion to have left the flue, and to open the flue before combustion can begin.

Abstract: A flue damper is rotated 360.degree. in a predetermined direction in 90.degree. increments to be selectively opened and closed in 90.degree. increments. The incremental rotation is accomplished by a motor driven timing mechanism with power to the motor being controlled by the timing mechanism and a single pole double throw relay.

Abstract: Disclosed is a fuel gas control for controlling the delivery of fuel gas. The present gas control comprises an inlet chamber having an inlet for receiving a supply of gas and an outlet chamber having an outlet for providing a supply of gas. The inlet and outlet chambers are connected by a valve opening. A valve is operatively associated with the opening. The valve has a closed position for preventing the flow of gas through the opening and an open position for permitting the flow of gas through the opening. The present control further comprises control chamber means for moving the valve between its open and closed positions in response to pressure variations within the control chamber means. The present control further comprises apparatus for directly connecting the control chamber means to a pressure signal from a power combustion air blower so that the valve is positioned in response to the pressure signal from the combustion air blower.

Abstract: A normally energized motor maintains a counterbalanced damper closed to block air inflow in a non-combustion condition of an appliance. Deenergization of the motor by thermostat control releases a rotor for displacement through a limited angular stroke. Through a lost-motion linkage connection the damper is displaced, in lagging relation to the rotor to the open position. The open position of the damper is detected by a sensor to open a fuel valve in the appliance.

Abstract: An integrated, closed loop system for controlling the fuel to air ratio in an induced draft combustion chamber which has a control pilot through which a draft is induced so that the fuel to air ratio in the control pilot chamber has a predetermined ratio to the fuel to air ratio in the primary combustion chamber.

Abstract: Apparatus for controlling the combustion of natural gas in a natural gas fired appliance is described. Exhaust gases are sampled and maintained at a predetermined constant temperature between the dew point and the steam point. The relative humity of the constant temperature gas is monitored by a hygrometer. Relative humidity deviations from a predetermined value result in output signals from the hygrometer to a control circuit. The control circuit is connected to regulators in the air intake or chimney of the appliance which regulate air intake to keep the relative humidity substantially constant and hence control combustion of the gas. In another embodiment the relative humidity of the exhaust gases and the combustion air intake are monitored by separate hygrometers which are linked to each other so that a change in the relative humidity of a gas affecting one hygrometer will compensate the other hygrometer and control combustion as before.

Abstract: The present control system and method for controlling the combustion chamber pressure in a non-linear combustion process is operative in relation to one or more combustion chambers each having a flue gas damper. In the case of a plurality of such chambers, the outlet duct associated with each chamber is connected to a common exhaust stack. This operation is in relation to a desired damper position control characteristic provided by a combination of process signals in a microprocessor computer apparatus. Information in the form of the combustion and pressure levels as supplied in an anticipative feed-forward control manner by a particular combustion chamber is utilized in conjunction with a variable gain characteristic determined by the actual position of the damper operative with that combustion chamber to determine the correct damper position for that chamber.

Abstract: An auxiliary exhaust system for use with a flue includes a conduit communicating at one end with an opening formed in the flue wall and a blower operable to introduce auxiliary air into the flue through the conduit. The conduit is angled so that the auxiliary air enters the flue with a velocity component extending in the downstream direction of the flow of the products of combustion to aid in venting the combustion unit. A damper located within the conduit operates an on-off switch in a blower control circuit which starts and stops the blower when the damper is opened and closed, respectively. The blower control circuit also includes an automatic combustion control which is responsive to flue temperature to increase the speed of the blower whenever the flue temperature is below a predetermined value and to decrease the blower speed whenever the flue temperature is above a predetermined value. The blower includes an access port which enables a fire extinguishing chemical to be introduced into the flue.

Abstract: A burner control system for gas fired apparatus of the powered blower vent type wherein a diaphagm valve for controlling the supply of gas to the main burner of the apparatus is operated by a gas bleed line which is subject to pressure regulation by a servo regulator valve. The bleed line is also subject to on-off control by pneumatically operated bleed valve means which are responsive to the subatmospheric fluid pressure produced in the exhaust vent of the apparatus by an exhaust blower to permit opening of the diaphragm valve only when the fluid pressure level within the exhaust vent is sufficiently below atmospheric pressure. The control system preferably includes switching circuit means which are effective to energize the exhaust blower only during the existence of a pilot burner flame adequate to ignite the main burner.

Abstract: A flue gas heat recovery apparatus for a forced air type furnace of the type having a furnace heat exchanger, a return air duct and a heated air duct, and a blower for passing air from the return air duct over the furnace heat exchanger to the heated air duct. The heat recovery apparatus includes a secondary heat exchanger mounted in the return air duct having its inlet connected to the outlet of the furnace heat exchanger and an induced draft fan having its inlet connected to the outlet of the secondary heat exchanger and its outlet connected through an outlet flue pipe to the chimney. A vane is mounted in the outlet flue pipe in the path of flow from the induced draft fan and is moved between a closed position when the fan is not operating, to an open position when the fan is operating, and a switch is operated by the vane to operate the burner control after the induced draft is in operation.

Abstract: Air trim control actuator mechanically connects a fuel flow device to an air flow device for setting the air to fuel ratio in combustion apparatus. An air to fuel ratio control unit is responsive to electrical input signals from an oxygen sensor that monitors the combustion products in the stack emissions. The air trim actuator includes a pivotally mounted input arm that is mechanically connected to the control unit and is pivoted to a preselected position corresponding to the selected boiler load. The input arm is connected by a link to an output arm which is pivoted through a preselected range of movement to control the position of the damper. The output arm has an elongated arcuate slot for receiving the end of the link. The output arm is pivoted to a position corresponding to the pivoted position of the input arm for selectively positioning the damper to provide air flow to the boiler for the desired air/fuel ratio.

Abstract: A control system for an induced or forced draft combustion apparatus has a single pressure transducer for providing an electrical signal indicative of pressures by alternately responding to the fuel pressure to the combustion apparatus and the fuel pressure plus the induced draft lower suction pressure. The signal output of the transducer is connected to a controller for controlling the fuel flow to maintain a predetermined fuel/air ratio for efficient and safe combustion of the fuel in the combustion apparatus.