Model (scale 1:4) of Edwards air pump in section

Model (scale 1:4) of Edwards air pump in section, worked by hand. One wood cut of three throw do., framed 7" x 5 3/4"

In this construction of air pump for a condensing steam engine, which was patented in 1894 by Mr. F. Edwards, there are neither foot nor bucket valves, a simplification which reduces the vertical height of the pump and increases the practical working speed. The pump is either attached to the side of the condenser and driven by rocking beams or is entirely separate from the engine and driven by an overhead crankshaft combined with it. The lower opening into the casing communicates with the bottom of the condenser while the upper one leads to the hot-well ; a side door near the top gives access to the delivery valves, and there is a safety valve to prevent any pressure accumulating when blowing through," or if the condenser should become hot. 66 The cover of the casing has a gland for the pump rod, but the use of a second gland is avoided by prolonging the stuffing box downward till it makes a joint with the internal cover carrying the delivery valves. The working pump barrel is a separate liner fixed to and supported by the casing. The bucket of the pump is a complete piston which during its down-stroke is forming a vacuum above it, but when nearly at the bottom of its stroke, it passes over radial ports through the barrel, through which passages the water and air from the condenser rush into the vacuum above the piston; the piston at the same time acts as a displacer in removing the fluids accumulated below it to its upper side. In the following up-stroke these fluids are discharged through the delivery valves in the cover as the piston approaches the top of its stroke; the piston is not packed, except by the water upon it, and the clearance volume at the top of its stroke is small. The bottom of the piston is made conical to avoid shock when displacing the water beneath it, and, owing to the way this water is thrown on to the upper side of the piston and there entrapped, the arrangement will work even without valves. The valves are of the disc type and are water sealed, but they can be easily removed or replaced when the pump is at work.