The Paxman Drop-Valve Engine was offered as a cheaper alternative to the Company's Lentz engine. The latter was more expensive because of the licence fee payable for use of the Lentz patents. Relatively few of these Paxman Drop-Valve engines appear to have been built.
The description and specifications below are taken from a Paxman catalogue thought to have been issued in late 1913 or in 1914.
The drop-valve engine, with admission and exhaust valves of the double-beat type, actuated by trip-gear and eccentrics driven from a side shaft, superseded the old Corliss and similar engines in consequence of its greater economy, the higher rotary speeds possible by the trip valve gear, and the suitability of this engine for a higher degree of superheat than was permissible with the Corliss type.
Our own trip-gear engine is of very high-class design, adapted for high working pressures up to 140 lb. per square inch, and suitable for superheated steam. The bearing surfaces are large, and the whole design is of the most rigid and substantial construction.
Design. The single cylinder, coupled-compound and tandem-compound engines are shown on pages 26, 28 and 30. The frame of the engine is of the trunk girder type, capable of withstanding all the working strains of the engine. The illustration on page 32 shows a coupled-compound drop-valve engine mounted on a special girder frame to render the engine suitable for working upon a very bad foundation. This frame is charged for extra, and designed to suit each special condition.
Drop-Valve Coupled Compound Engine
Cylinders. These are cast of a special mixture of iron, free from imperfections, fitted with a hard, close-grained, cast-iron liner, truly bored and machined. They are covered with non-conducting composition, and neatly lagged with planished blue sheet steel.
Crankshaft. Is of the best forged steel, turned all over, the outer end, beyond the flywheel, being carried by an outside bearing.
Valve Gear. The valve gear is of the "trip" variety. Both admission and exhaust valves are of the circular double-seated type, the steam admission valves being operated through trip levers and rods working from eccentrics on the side shaft. The exhaust valves are placed at the bottom of the cylinder which they drain. They are quietly opened and closed by suitable rollers and levers worked from the side shaft.
Drop-Valve Tandem Compound Engine
Lubrication. The high-pressure cylinder is provided with sight-feed lubricator, the crank-pin with centrifugal oiler, and all other working parts with drop-feed lubricators.
Governor. This is of our improved high-speed type, driven from the side shaft by suitable chain, and carried on a neat cast-iron stand. It is extremely sensitive, and capable of controlling the engine under varying conditions of load.
Flywheel. This is of suitable size for giving off the full power of the engine, carefully machined, and when necessary cast in halves. Teeth are cast in the rim for receiving the barring gear. If required, it can be grooved for driving ropes at an extra charge.
Handrails. Polished handrails are provided to guard the crank.
Fittings. The fittings supplied with these engines are of the highest class, and comprise : Stop valve, sight-feed lubricator to high pressure cylinder, drop-feed lubricators, cylinder drain cocks, complete set of spanners, oil feeder, and foundation bolts and plates.
In the table below columns 9 and 10 show the diameters of steam and exhaust pipes respectively, columns 11 and 12 show the dimensions of flywheels turned for belt drive, columns 13 and 14 refer to flywheels grooved for rope drive showing the number and diameter of the rope grooves.
| Cylinder | Brake Horse-Power | Pipe dia. (inches) | Flywheel | Speed RPM |
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| Dia. (ins.) | Stroke (ins.) | 80 lbs | 100 lbs | 120 lbs | Turned | Grooved | ||||||||
| Nor. Load | Max. Load | Nor. Load | Max. Load | Nor. Load | Max. Load | Stm | Exh | Dia | Face | No | Dia | |||
| 9 | 21 | 26 | 38 | 29 | 42 | 32 | 45 | 3 | 3½ | 8' | 7" | 3 | 1¼" | 135 |
| 10½ | 24 | 38 | 56 | 42 | 60 | 45 | 62 | 3½ | 4 | 9' | 9" | 3 | 1½" | 125 |
| 12 | 27 | 52 | 75 | 56 | 80 | 60 | 83 | 3½ | 4½ | 10' | 12" | 4 | 1½" | 115 |
| 14 | 30 | 72 | 100 | 77 | 110 | 82 | 115 | 4 | 5 | 10' | 15" | 5 | 1½" | 105 |
| 16 | 33 | 98 | 140 | 105 | 150 | 112 | 156 | 5 | 6 | 12' | 18" | 5 | 1¾" | 100 |
| 18 | 36 | 125 | 180 | 135 | 195 | 145 | 200 | 6 | 7 | 13' | 22" | 6 | 1¾" | 95 |
| 20 | 42 | 170 | 230 | 185 | 260 | 200 | 275 | 6 | 7 | 14' | 29" | 7 | 1¾" | 90 |
The specifications given in the table below were common to both types. Columns 10 and 11 show the diameters of steam and exhaust pipes respectively, columns 12 and 13 show the dimensions of flywheels turned for belt drive, columns 14 and 15 refer to flywheels grooved for rope drive showing the number and diameter of the rope grooves.
| Cylinders | Brake Horse-Power | Pipe dia. (inches) | Flywheel | Speed RPM |
|||||||||||
| Diameters (inches) | Stroke (ins.) | 100 lbs | 120 lbs | 140 lbs | Turned | Grooved | |||||||||
| Nor. Load | Max. Load | Nor. Load | Max. Load | Nor. Load | Max. Load | Stm | Exh | Dia | Face | No | Dia | ||||
| 9 | 15 | 21 | 63 | 76 | 68 | 84 | 73 | 90 | 3 | 5 | 8' | 11" | 5 | 1¼" | 135 |
| 10½ | 17 | 24 | 86 | 104 | 93 | 114 | 100 | 125 | 3½ | 5½ | 9' | 15" | 5 | 1½" | 125 |
| 12 | 20 | 27 | 124 | 150 | 133 | 162 | 140 | 180 | 3½ | 7 | 10' | 18" | 7 | 1½" | 115 |
| 14 | 23 | 30 | 165 | 200 | 180 | 220 | 190 | 240 | 4 | 8 | 10' | 23" | 8 | 1½" | 105 |
| 16 | 26 | 33 | 220 | 265 | 240 | 290 | 255 | 320 | 5 | 8½ | 12' | 26" | 8 | 1¾" | 100 |
| 18 | 30 | 36 | 305 | 365 | 330 | 400 | 350 | 440 | 6 | 10 | 13' | 33" | 10 | 1¾" | 95 |
| 20 | 34 | 42 | 435 | 520 | 470 | 570 | 500 | 620 | 6 | 12 | 14' | 42" | 13 | 1¾" | 90 |
Page updated: 05 JAN 2009