Forced draft furnace safety system

Claim 2

The improvement in a forced draft furnace safety system for use with a furnace having a centrifugal blower for moving air and combustion gases through the furnace, comprising: air pressure sampling means including a tube connected so as to sense the air pressure at the input to the centrifugal blower, and means for controlling the flow of fuel to the furnace in response thereto so as to prevent such flow when there is insufficient draft and to allow such flow when there is sufficient draft.

Claim 3

The improvement as defined in claim 1 wherein: said tube has pressure sensing in its opening positioned at the lip of the opening into the blower on a radius from the center of that opening which makes an angle to the radius parallel to the direction of air flow from the blower as measured therefrom in the direction of rotation of the blower wheel, of about 45* to about 95*.

Claim 4

The improvement as defined in claim 2 wherein said angle is equal to approximately 70*.

Claim 5

A furnace comprising: a source of flammable gas, (12) a burner, (16) a control valve (14) for connecting or not connecting said source and said burner; a heat exchanger (18) mounted adjacent to said burner with passages for air and flue gases to pass therethrough; a gas collection box (20) connected to said heat exchanger for receiving the air and flue gases; a centrifugal blower (26) having a generally circular inlet coupled to said gas collection box for receiving air and flue gases therefrom, a rotary mounted blower wheel and an exit port for discharging propelled air and flue gases from the blower in a direction generally tangential to the blower wheel; an air pressure transmitting tube (34) having an inlet mounted so that the inlet is positioned adjacent to the blower generally circular inlet, an air pressure differential switch (36) coupled to said tube and to the ambient air pressure for activation in response thereto, and coupled to said control valve for controlling said valve so as to not connect said gas source to said burner in the absence of a sufficient difference in pressure between said tube and ambient air pressure.

Claim 6

A furnace comprising: a source of flammable gas, (12) a burner, (16) a control valve (14) for connecting or not connecting said source and said burner; a heat exchanger (18) mounted adjacent to said burner with passages for air and flue gases to pass therethrough; a gas collection box (20) connected to said heat exchanger for receiving the air and flue gases; a centrifugal blower (26) having a generally circular inlet coupled to said gas collection box for receiving air and flue gases therefrom, a rotary mounted blower wheel and an exit port for discharging propelled air and flue gases from the blower in a direction generally tangential to the blower wheel; an air pressure transmitting tube (34) having an inlet mounted so that the inlet is positioned adjacent to the blower generally circular inlet, an air pressure differential switch (36) coupled to said tube and to the ambient air pressure for activation in response thereto, and coupled to said control valve for controlling said valve so as to not connect said gas source to said burner in the absence of a sufficient difference in pressure between said tube and ambient air pressure.

Claim 7

The furnace as defined in claim 4 wherein: said tube is positioned so as to sample the drop in air pressure at said inlet at a point adjacent to and interior of the rim of said blower opening, along a radius from the center thereof which radius is at about 70* from, in the direction of travel of the blower wheel, the tangential direction of air flow from the exit port of said blower.