Sir William George Armstrong in 1836 observed an overshot water-wheel which employed about 20 feet of the fall of a small stream, while several hundred feet of the entire descent remained unproductive. It naturally occurred to him that if the stream were conducted in a pipe from the highest available point, and the pressure of the contained column were caused to act mechanically at the bottom, the power afforded might be increased in proportion to the greater fall brought into operation. The question how this object could be accomplished took a lasting hold of his mind, and he applied himself to devise a machine which would answer the purpose.
This first water pressure engine machine consisting of a wheel with a flat rim, containing four equidistant pistons folding into circular apertures, and intersecting longitudinally a curved tube
open at the lower end, and communicating at the upper end with the supply pipe. The pistons open out as they enter the tube and fold up on leaving it, and each piston takes the pressure of the
column before the preceding one loses it. The opening and closing of the pistons in the order required is effected by external cams and slides giving motion to the pistons through the axles on
which they turn.
The scheme thus published shared the usual fate of mere pen and-ink inventions. It remained wholly unnoticed, and the Armstrong seeing that no one was likely to make trial of his machine resolved to do so himself. He accordingly got a working model made upon a scale sufficiently large to test the efficiency of the invention. It was completed in the latter part of 1839, and tried, first in Newcastle and afterwards in Gateshead, by connecting it with the town water pipes. From this source a supply of water was obtained under a pressure representing a column of 131 feet, and the wheel making thirty revolutions a minute developed about 5 HP.
The limited supply of water prevented a higher speed
being attained, but the machine only required a larger pipe to enable it to work at a higher velocity and yield a proportionately higher power. It worked extremely well, and its co-efficient of effect was high.
Armstrong continuing to invent hydraulic water engines, used [[http://www.machine-history.com/Armstrong%20Hydraulic%20Crane|piston and accumulator systems to power cranes]] and feed the growing industrial world.