Draft Controllers

A draft controller for furnaces comprises an auxiliary channel in communication both with ambient air and the flue of the furnace, a main draft control means for regulating the entrance of ambient, auxiliary draft air into the flue, and auxiliary draft control means mounted in the auxiliary channel for dampening the effect of extreme changes in external conditions on the main draft control means. Thus, uniform draft and efficient combustion is maintained in the furnace under a wide variety of conditions. The main draft control means comprises counter-balanced draft control plates which are initially set in an open position so that they can either open or close in order to efficiently regulate the draft in the flue. The auxiliary draft control means comprises, in one embodiment, an isolation damper plate rotationally mounted in the auxiliary channel, or, in a second embodiment, a set of louvred panels.

Improper draft control has been the major contributing factor in inefficient furnace operation. Changes in the draft volume or velocity may be caused by many external factors, such as the amount of crude oil fed into the furnace or changes in the ambient condition surrounding the furnace. Also, a decrease in temperature of the surrounding air will increase its density, again resulting in excess oxygen conditions. It is common to compensate for these changes in draft intensity by providing a furnace with a damper plate in the flue to control the velocity of the draft. However, these flue dampers must be manually operated. Therefore, their position must be adjusted with each change in furnace operating conditions, whether it is a change in fuel rate or ambient conditions. This method of draft control increases the labor costs associated with furnace operation. Furthermore, since these flue dampers are exposed to the hot flue gases, their bearings deteriorate very rapidly, causing the damper to stick and become inoperable. The draft controller of the present invention overcomes the shortcomings of the prior art by providing both main and auxiliary draft control means which maintain efficient control over the combustion in the furnace regardless of both mild and extreme changes in furnace operating conditions, both slight and extreme.

The draft controller is comprised of an auxiliary channel in communication with the main flue of the furnace, a draft box mounted at the end of the auxiliary channel and open to ambient air, a main draft control means mounted in the draft box, and an auxiliary draft control means mounted in the auxiliary channel. The main draft control means, which preferably is comprised of one or more counter-balanced draft control plates rotationally mounted at the mouth of the draft box, is sufficient to maintain uniform draft control under slight to moderate changes in operating conditions. That is, if the furnace operating conditions vary moderately due to light winds, changes in atmospheric pressure, or small changes in the rate of fuel consumption, the present main draft control means provides an even draft control for efficient combustion conditions.