Abstract: A gaseous fuel-air premix combustion burner is disclosed wherein the production of oxides of nitrogen can be inhibited. By blowing secondary air onto at least a maximum temperature region of a secondary reaction region of a gaseous fuel-air premix combustion flame, it is possible to minimize the production of oxides of nitrogen not only in regions of the flame where the volume of primary air is smaller or larger than the theoretical volume of air but also in the vicinity of a region of the theoretical volume of air, whereby the area of a region where the production of oxides of nitrogen is reduced can be increased.

Abstract: A gas burner of a low noise, high load combustion type, which produces a flame of a mixture gas prepared or mixed preliminarily. In this burner, an inner flame of a laminar flow is formed and then secondary air of a turbulent flow is supplied to an outer flame portion of a trailing stream of the inner flame from secondary air ports. The inner flame is provided in the form of a laminar flame, and secondary air is thus supplied to an outer flame portion of the inner flame, so that combustion takes place at a low noise level. In addition, since the secondary air is supplied at a turbulent flow, the secondary air may be fixed with an outer flame quickly, thus enabling high load burning or combustion. Furthermore, in case secondary air is supplied from secondary air ports in the form of a laminar flow at a relatively high flow velocity, and then rendered turbulent, downstream of the secondary air ports, then the size of a burner may be reduced, with an accompanying simplified construction.

Abstract: The disclosure is concerned with an axial fan having a casing. Unacceptably high level of noise and low discharge pressure inherent in axial fans are attributable to a counter flow of fluid taking place through the gap between the radially outer ends of the rotating blades and the casing. The invention is directed to preventing the counter flow by providing guide vanes disposed in the gap and inclined symmetrically with the rotating blade, thereby to provide enhanced output flow rate and discharge pressure, as well as to reduce the level of noise. The invention is applicable also to such axial fan as having a baffle plate on the suction side of the rotating blade in the proximity thereof.

Abstract: A safety test circuit for a combustion control apparatus. This safety test circuit is used to check the off-failure of a safety transistor actuating a safety relay which acts to stop the operation of controlled units in the event of mal-combustion or the like, and also to check the on-failure of a control transistor actuating a control relay which controls the controlled units. An operation instruction signal and the collector potential of the safety transistor are applied to a logic circuit including a flip-flop and logic gates so that the off-failure of the safety transistor can be driven to check, utilizing the electrical signal propagation delay time of the elements constituting the logic circuit, before the propagation delay time has elapsed. The logic circuit is also used for similarly checking the on-failure of the control transistor.