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Piston valves are one form of valve used to control the flow of steam within a steam engine or locomotive. They control the admission of steam into the cylinders and its subsequent exhausting, enabling a locomotive to move under its own power. The valve consists of two piston heads on a common spindle moving inside a steam chest, which is ...
A locomotive's direction of travel and cut-off are set from the cab by using a reversing lever or screw reverser actuating a rod reaching to the valve gear proper. Some larger steam engines employ a power reverse, which is a servo mechanism, usually powered by steam. This makes control of the reversing gear easier for the driver.
An expansion valve is a secondary valve within a steam engine. They represent an intermediate step between steam engines with non-expansive working and later valve gears that could provide for expansion by controlling the motion of a single valve. Expansion valves were used for stationary engines and marine engines. [1]
Double-beat poppet valves became widely used during the nineteenth century. Francis Stevens invented the Stevens valve gear, a double beat poppet valve, in 1839. It was used throughout the nineteenth century and in the early years of the 20th, on side-wheel paddle steamer engines, including the grasshopper engine, in the United States. [4]
During the 1830s, the most popular valve drive for steam locomotives was known as gab motion in the United Kingdom and V-hook motion in the United States. [3] The gab motion incorporated two sets of eccentrics and rods for each cylinder; one eccentric was set to give forward and the other backwards motion to the engine and one or the other could accordingly engage with a pin driving the ...
As the piston descends, the valve moves upwards to admit steam below the piston and release exhaust from above. The slide valve is a rectilinear valve used to control the admission of steam into and emission of exhaust from the cylinder of a steam engine. The image description page explains how this SVG animation can be viewed
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The Hackworth valve gear is a design of valve gear used to regulate the flow of steam to the pistons in steam engines. It is a radial gear , with an actuating lever driven from the crank. The drive may be taken directly from the crank or indirectly via a return crank (as in all pictures).