Ashton Frost High And Low Pressure Cylinders
The steam engines are of the horizontal tandem compound rotative design. This description deserves a few words of explanation. Horizontal refers to the layout of the steam engine and pumps, tandem means that the two steam cylinders are arranged one behind the other on the same piston rod. Compound means that there is both a high pressure cylinder and a low pressure cylinder and rotative refers to the use of the flywheel to achieve continuous motion.
Steam from the boiler is admitted to the high pressure cylinder via one of two Corliss valves at the top of the cylinder. Operation of the valve is via a rod linkage connected to an eccentric on the flywheel crankshaft, which also operates the low-pressure cylinder inlet valves. The high pressure inlet valve gear is tripped and closed by spring-loaded dashpots, with the cut off point being automatically controlled by a linkage connected to the governor. Thus the volume of steam entering the high pressure cylinder is governed and in turn regulates the speed of the steam engine.
Two other eccentrics and rod linkages operate the exhaust valves that are located at the bottom of each cylinder. The valves on the low pressure cylinder are timed to open slightly earlier than the high pressure cylinder valves, in order to obtain the maximum benefit from the vacuum created by the condenser.
Steam is prevented from escaping from the cylinders by the use of a United States Metallic Packing at each end of the two cylinders. These packings were described by The United States Metallic Packing Company as "Automatic" "Self-Adjusting" and "Steam Setting", "been designed with the view to increasing the efficiency of Steam Engines by decreasing the friction on the piston rods."
For those who would like to find out more about these packings an advertising leaflet giving details can be downloaded below.
Click for United States Metallic Packing leaflet
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