Todd, Leonard Jennett

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fl. 1885 London, England
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English (?) patentee of steam engines incorporating the uniflow principle.
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In a uniflow system, the steam enters a steam engine cylinder at one end, pushes the pistons along, and exhausts through a ring of ports at the centre of the cylinder that are uncovered by movement of the piston. The piston is returned by steam then entering the other end of the cylinder, moving the piston arrangement back, and again making its exit through the central ports. This gave the thermodynamic advantage of the cylinder ends remaining hot and the centre colder with reheating the ends of the cylinder through compression of the residual steam. The principle was first patented by Jacob Perkins in England in 1827 and was tried in America in 1856.
Little is known about Todd. The addresses given in his patent specifications show that he was living first at South Hornsey and then Stoke Newington, both in Middlesex (now in London). No obituary notices have been traced. He took out a patent in 1885 for a "terminal exhaust engine" and followed this with two more in 1886 and 1887. His aim was to "produce a double acting steam engine which shall work more efficiently, which shall produce and maintain within itself an improved gradation of temperature extending from each of its two Hot Inlets to its common central Cold Outlet". His later patents show the problems he faced with finding suitable valve gears and the compression developing during the return stroke of the piston. It was this last problem, particularly when starting a condensing engine, that probably defeated him through excessive compression pressures. There is some evidence that he hoped to apply his engines to railway locomotives.
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Bibliography
1885, British patent no. 7,301 (terminal exhaust engine). 1886, British patent no. 2,132.
1887, British patent no. 6,666.
Further Reading
R.L.Hills, 1989, Power from Steam. A History of the Stationary Steam Engine, Cambridge University Press (provides the fullest discussion of his patents). H.W.Dickinson, 1938, A Short History of the Steam Engine, Cambridge University Press.
J.Stumpf, 1912, The Una-Flow Steam Engine, Munich: R.Oldenbourg.
RLH

Biographical history of technology. - Taylor & Francis e-Librar. . 2005.

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