Excerpt from Catalogue of Watt Centenary Exhibition About this date an important modification was made in the design of the cylinder. Watt's first engines had their cylinders enclosed in a steam case and the upper side of the piston was in constant communication with the boiler steam and with the case. The modification consisted in the introduction of an upper regulator valve, and in separating the jacket steam from the working steam. The regulator was used only when the engine was underloaded, either as a hand-adjusted throttle valve or as a mechanically operated valve to cut off the steam before the end of the stroke and to use the steam expansively. The pumping engines were usually made with unequal-armed beams so that the pump stroke would not exceed 6 ft. Or 7 ft which the Cornishmen found the best in practice. The valves are shown in detail; levers and pitch chains are used to lift them. (n. B. - The rack and sector came later). The exhaust valve consists of a cylinder with a closed top sliding on an internal guide and seating on the lower edge of its rim. In the top is a small conical pilot valve which opens first and admits the steam to the interior of the cylinder so as to balance it and render it easy to lift. A note on the drawing, in Watt's writing, shows that this was a new construction at this date it is an early instance of a balanced valve. About the Publisher Forgotten Books publishes hundreds of thousands of rare and classic books. Find more at www.forgottenbooks.com This book is a reproduction of an important historical work. Forgotten Books uses state-of-the-art technology to digitally reconstruct the work, preserving the original format whilst repairing imperfections present in the aged copy. In rare cases, an imperfection in the original, such as a blemish or missing page, may be replicated in our edition. We do, however, repair the vast majority of imperfections successfully; any imperfections that remain are intentionally left to preserve the state of such historical works.