Model of Leblanc air pump

Model in wood, full size, in section of Leblanc air pump

This is a form of rotary air pump, patented by Mons. M. Leblanc in 1905 and 1907; it is simple in construction and is capable of producing a high vacuum, such as is required in the condenser of a steam turbine where a large ratio of expansion is necessary for high efficiency. The pump consists of a cylindrical casing containing a turbine wheel, through which water flows radially outwards from a port or nozzle. This nozzle is mounted on a disc so curved as to give an easy passage to the water, which enters the casing by a pipe on one side of it. The shaft passes through stuffing boxes at each side, and outside these are the bearings supported by extensions of the casing. A pipe, formed in one with the main casing and placed tangentially to it, is connected with the condenser at its upper end, and contains a converging tube close to the wheel, while a diverging discharge pipe is fitted to its lower end. The wheel is rotated at a high speed, usually by a directly connected electric motor, in the opposite direction to which it would rotate if driven by the water, and it throws the water from the nozzle into the diffusing cone in a succession of thin sheets having a high velocity. These sheets com- pletely fill the tube, entrap between them the air and non-condensable gases coming from the condenser, and carry them out against the atmospheric pressure. A steam ejector is fitted to the discharge pipe to start the pump. The pump wheel is 15 in. diam., the air inlet 4 in. diam., and the water inlet 5 in. diam.; a pump of this size is suitable for a condenser dealing with 15,000 cub. ft. of steam per hour. It will produce a vacuum of 28.5 in., with cooling water at 15 deg. C., and runs at 960 rev. per min., requiring an expenditure of 9.5-10 brake h.p.