The date of the first patent on these pumps was September 7, 1841. It was issued on a small pump used for supplying feed water to a steam boiler, and consisted of one steam cylinder connected to a force pump, and so arranged that by the use of levers, trips, springs, and other connections between the piston rod and the slide valve, the movement of the piston rod controlled the movements of the slide valve to an extent that not only regulated the length of the stroke of the piston, but reversed its motion. This pump was placed alongside of the steam boiler, and was so connected by means of pipes and levers and floats within the boiler, that when the water fell below the proper level in the boiler, it would start the pump, and stop it when the water rose too high.
Note.—At the head of a list consisting of two names only, who, on the foremost pages of “The American Society of Mechanical Engineers,” are recorded as the “Honorary Members in Perpetuity” of that large society, and standing as well at the head of that long and increasing list of members who have accomplished their work on earth, may be seen the name of Henry Rossiter Worthington, the inventor and original builder of the “direct-acting steam pump.”
Feeling how incomplete was an invention which did not provide against the intermittent action of the pump, Mr. Worthington devoted much time and study to correct this trouble, and a few years later he brought out an improved pump which, in its simplicity of parts, certainty of action, and cheapness of construction more than rivaled the original invention itself. This pump is now universally known as the “Direct-Acting Duplex Steam Pump.”
In the main, the construction of the steam ends and the water ends of the duplex pump differs but slightly from those of the single-acting pump, but the mechanism which operates the steam valves is different, and the effect on the water column was marvelously different; the principle upon which it operates is this:
Two pumps of similar construction are placed side by side, a lever attached to the piston rod of each pump connects to the slide valve of the opposite steam cylinder; thus the movement of each piston, instead of operating its own slide valve as in the single pump, operates the slide valve of the opposite cylinder. The effect of this arrangement is, that as the piston or plunger of one pump arrives near the end of its stroke, the plunger or piston of the other begins its movement, thus alternately taking up the load of the water column, producing a regular, steady, onward flow of water, without the unusual strains induced by such a column when suddenly arrested or started in motion.
While the “duplex steam pump” overcame one of the greatest objections to the former single pump, there still remained in this class of pumping machinery one other difficulty. It did not use steam expansively.
This not only debarred it from competing with other engines where a large quantity of water was required to be raised, and where the cost of fuel was an item of importance, but as well prevented the pump from taking rank among the hydraulic appliances required in supplying towns and cities.
This objection was one which seemed insurmountable, steam in them could not be used economically. Applied to the propulsion of the plunger or piston of this pump it must be of sufficient quantity, and pressure, to overcome the height of the column of water on the pump, together with its friction through the pump and its connections, at the very beginning of the stroke; and it must be maintained, both as to its volume, and its pressure up to the very last part of the stroke. Any diminution, either of volume or pressure, during any part of the stroke would simply bring the pump to a stop. This apparent inability to cut off the steam in the steam cylinder, and to complete the stroke of the pump by the aid of the steam remaining in the cylinder, and by its expansive force, had debarred this pump from coming into general use for large water works. How this, the only remaining objection to their use for such purposes, was overcome, forms an interesting chapter in the history of the “Direct-Acting Steam Pump.”