The Severn Tunnel/Appendix
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Appendix. Description of the large pumps by Messrs. Harvey, of Hayle Foundry.
DESCRIPTION OF THE LARGE PUMPS BY MESSRS. HARVEY, OF HAYLE FOUNDRY.
Six engines, with a stroke of 10 feet in the cylinder, of the type known as the Single-Acting Cornish Beam Engine, are erected in one house—three on either side of a pit, which is 29 feet in diameter, and 180 feet deep. Those on one side are connected to three pumps of the plunger type; those on the other, to three drawing-lifts, or bucket-pumps.
These engines, as well as all the other permanent engines at this station, were erected by Messrs. Harvey and Co., Limited, of Hayle, Cornwall; as the six engines are similar in every respect, and represent very fairly the type of engine adopted throughout, a description of one will serve for the whole.
All parts of the engines are duplicates, thus any one piston-rod or valve will serve for either engine.
The pumps, valve-boxes, and valves of either type, are also duplicates.
Only a few spare parts, therefore, are required in case any unforeseen accident should disable one of the engines.
Cylinder.The cylinder is of 70 inches internal diameter, by 12 feet long. It is securely fixed in an outer case, leaving a space of 1½ inches between the two, which, when working, is filled with steam direct from the boiler, thus preventing undue condensation in the working cylinder. The condensed steam from this case is conducted through the drain-pipes back again to the boilers.
Cylinder Bottom.The cylinder and case are mounted on a strong cast-iron bottom, and attached thereto by 36-1⅜ inch bolts.
The cylinder bottom has cast on it the aperture to which the exhaust nozzle is attached, and is secured by five long hold-down bolts to a massive foundation of masonry 15 feet in depth.
Piston.The piston is of the ordinary metallic kind, having a deep spring ring, packed at the back with rubber or gasket, and secured by a joint ring ground in true on piston and ring.
The rod, of wrought-iron, is connected to the piston by a deep cone, and secured by a wrought-iron cotter and fore-lock.
Cylinder Cover.The cylinder-cover is of cast-iron, fitted with a deep stuffing-box, in which provision is made for a circulation of steam at boiler pressure, which prevents the possibility of air leaking through into the cylinder.
The cover is also fitted with an outer case of polished cast-iron, and with suitable arrangements for lubricating the piston and cylinder.
Nozzles and Valves.The steam, in its passage through the cylinder, is regulated by four valves, three of which—the governor, steam, and equilibrium—are fixed in the top nozzle, and the fourth—the exhaust valve—is fixed in the bottom nozzle.
All these valves are of the Cornish double-beat pattern, and are cast of gun-metal.
The governor valve is entirely under the control of the engine-driver, who can regulate the flow of steam according to any distinct variation of the pressure in the boiler.
The steam equilibrium and exhaust valves are worked by the Cornish valve-gear.
The engine load being constant, no variation is required in the expansion, and the point of cut-off is therefore definitely fixed at about one-fourth of the length of stroke. Provision is made for cutting off the steam at from one-eighth to three-quarters of the stroke if required.
The top and bottom nozzles are connected by two vertical polished pipes, one of which is used as a steam-pipe, and the other conducts the steam—on the opening of the equilibrium valve—from top to bottom of piston. This pipe is fitted with a throttle-valve (under the control of the driver) which regulates the speed of the engine on the return or outdoor stroke.
Cataract. The number of strokes performed by the engine is controlled by the cataract, which automatically regulates it from one to about fifteen strokes per minute.
By an ingenious contrivance the speed of the six engines is regulated by two cataracts, which, although allowing each engine to perform the same number of strokes per minute, so regulates them that no two engines make their stroke at the same moment, this insures uniform pressure of steam, and an even discharge of water into the culverts. Provision is made in case either of the engines remains idle.
Engine Beam.The engine-beam is of wrought-iron throughout, being built up of plates and angles having a web of strong section, and made of double faggoted iron secured to, and entirely surrounding, the outer edge. This web alone is sufficiently strong to resist the entire load. The centres are all accurately bored to receive the respective pins. The main pin, or gudgeon, is secured by two keys placed at the quarters, and rests in two massive gun-metal bearings, supported by heavy cast-iron stools and wall-plate. The wall-plate is secured to the main wall of building.
Parallel Motion.A parallel motion of polished wrought-iron is fitted to each end of the beam, which parallelizes the path of piston and pump-rods, the anchorage of same being attached to strong wrought-iron spring beams and girders extending across the building, and secured to the wall.
The piston and pump-rods are attached to these motions by strong wrought-iron caps.
Condenser.The condenser is of the surface-condensing type, consisting of about 400 galvanized wrought-iron tubes, secured by screwed ends into wrought-iron plates above and below. These plates are bolted on to a cast-iron head and bottom-piece, the latter also carrying the air-pump, which is of the ordinary type.
The whole is contained in a large cast-iron cistern, supplied with a continuous stream of cold water by a pump worked from the main pump-rod.
The exhaust steam passes from the cylinder through the tubes, and being condensed by the action of the cold water without, collects at the bottom of the condenser, and is pumped back into the boilers.
Pumps.The pumps are of two kinds, three being of the bucket-lift type and three of the plunger, all with a stroke of 9 feet.
Bucket-Pump.The bucket-lift has a working barrel of 35 inches internal diameter, with a gun-metal lining throughout, and fitted with a gun-metal bucket, carrying Husband’s patent four-beat valve on same. The bucket is made extra deep, and without packing.
It is connected with cotter and cap connections to the wrought-iron rods 6½ inches diameter.
The bottom valve is also of gun-metal of the four-beat type, seated in a strong cast-iron valve-box, and secured thereto by a suitable steel crosshead. A large circular door is provided for the ready removal of valves. The valve-box rests on a strong cast-iron windbore, having from two to three thousand 1¼ inch holes in it, the whole being supported by, and secured to, massive foundation-plates at the bottom of well.
The rising-main is of cast-iron of 39 inches diameter, in sections 9 feet long, having a wrought-iron collar-launder at the head for the delivery of the water into the culverts. The pump-head is provided with a suitable guide for the pump-rods.
Plunger Lift.Each plunger-lift has a plunger-pole, 35 inches diameter, accurately turned, and working into a pole-case, having a suitable stuffing-box with gun-metal bushings.
Plunger.This plunger-pole is surmounted with a large load-box, which is filled with cast-iron weights, which, together with the rods, balance the column of water in the rising main. The pump-rods are of wrought-iron similar to those in the bucket-lift, and are guided at four equidistant points in the shaft by suitable guides, secured to strong iron girders built into the walls of the pit.
Valves. The suction and delivery valves are of gun-metal and of the four-beat type, as before described, seated in strong cast-iron valve-boxes, having windbores and bed-plates similar to those of the bucket-lift.
The pole-cases are mounted on, and secured to, a strong wrought-iron box-girder filled with concrete, and built into the walls of the pit.
The rising-main is of cast-iron 32 inches diameter, and in sections 9 feet long.
The flanges are all accurately faced, and those of the valve-boxes and pole-cases have a strong wrought-iron ring shrunk on them as an extra precaution against sudden shocks.
All pumps and valve-boxes, with valves in place, were tested by hydraulic pressure on the contractor’s works to upwards of four times the working load.
Fresh-water Pumps.To supply the condensers with cold water, there are six 12-inch house-lifts in the 29 feet pit, worked by a set-off from the iron pump-rods, one to each engine. These are of the plunger type, and take their supply from the respective pump-heads of the rising-mains, and deliver same into the several condensing cisterns.
There are also two 12-inch fresh-water pumps in the same pit. They are worked off the 35-inch plunger-lifts by a set-off placed immediately over the plunger-pole, and they take their supply from a fresh-water spring, cut at or about the bottom of the well.
They are also of the plunger type, having gun-metal four-beat valves and cast-iron rising-mains, delivering fresh-water into a reservoir at the surface to supply the neighbourhood.
The pit is amply provided with various ladders and stages, affording easy access to all parts of the pump-work. The valve-boxes being all about the same level, and the most important part of the system, a platform is placed there, on which are stored the spare valves.
A simple contrivance is also provided by which the valves can be changed very rapidly.
The engine-house is traversed in its entire length by a powerful traveller, capable of handling any part of the engine or pumps.
Boilers.Steam is supplied to the engines from a battery of twelve double furnace Lancashire boilers placed in an adjoining building.
Two main steam-pipes connect the boilers with the engines. These pipes are arranged with sluice-valves, so that the engines can be worked singly or all together.
Temporary Pumps.The temporary pumps used during the construction of the works are as follows:
At the Iron Pit, Sudbrook, two 26-inch plungers (the Bulls), with 10-foot stroke, raising 231 gallons per stroke each, or 462 the two together.
Also one 35-inch bucket-pump, with 9-foot stroke, raising 376 gallons per stroke.
At the New (12-foot) Pit at Sudbrook, a 28-inch plunger-pump, with 10-foot stroke, raising 267 gallons per stroke; also two 18-inch plunger-pumps, with 10-foot stroke, raising 110 gallons per stroke each, or 220 gallons the two together.
At the Old (15-foot) Pit at Sudbrook, erected specially to pump the Great Spring, a 37-inch plunger-pump, with 10-foot stroke, raising 467 gallons per stroke; also a 35-inch bucket, with 9-foot stroke, raising 376 gallons per stroke; and a 31-inch bucket, with 9-foot stroke, raising 298 gallons per stroke.
At Five-mile-four-chain Pit, one 31-inch bucket-pump, 9-foot stroke, raising 298 gallons per stroke ; one 28-inch bucket, 9-foot stroke, raising 240 gallons per stroke; two 18-inch plungers, 8-foot stroke, raising 88 gallons each per stroke, or 176 gallons the two; also a 5-inch and an 8-inch plunger, the two raising 25 gallons per stroke.
At the Marsh Pit, two 15½-inch plunger-pumps, with 7-foot stroke, the two raising 114 gallons per stroke, and a 15-inch bucket, raising 54 gallons per stroke.
At the Hill Pit, two 15½-inch plunger-pumps, the two raising 114 gallons per stroke.
At Benacre Bridge, two 15-inch bucket-pumps, raising 108 gallons the two.
Taking the average number of strokes per minute as ten, these pumps represent 36,000 gallons per minute. The actual delivery will be about 20 per cent. less than the theoretical, so that these pumps would raise about 27,000 gallons per minute.
On the Gloucestershire side, at Sea-wall Shaft, there were two 15½-inch plungers and two 15-inch bucket-pumps, raising in all 224 gallons per stroke.
At Green Lane, for the open cutting, two 15-inch bucket-pumps, raising 108 gallons per stroke.
At Ableton Lane, for the bridge, the same.
The total number of pumps provided during construction was thirty, and these were capable of raising 44 million gallons per day.
Four of these pumps—the 37-inch plunger, the 35-inch bucket, and the two 26-inch plungers (the Bulls)—are now permanent pumps.
Permanent Pumps.The permanent pumps provided for the Great Spring and the drainage of the tunnel and cuttings are:
At the Iron Pit, Sudbrook—two 26-inch plungers, with 10-foot stroke, raising 231 gallons per stroke each, the steam cylinders being 50 inches diameter, stroke same as pump; horse-power per stroke from water raised 13·2 per engine, or 15·9 from indicator; ordinary strokes per minute 7, maximum 12; lift for water 190 feet. Also one 35-inch bucket-pump, with 9-foot stroke, raising 376 gallons per stroke; the steam cylinder 75 inches diameter, stroke 10 feet; beam engine, horse-power per stroke from water raised 21·7, from indicator 25·7; ordinary strokes per minute 10, maximum 12; lift 190 feet.
In the 12-foot Shaft, Sudbrook, one 37-inch plunger-pump, with 10-foot stroke, raising 467 gallons per stroke; the steam cylinder 70 inches diameter, stroke 10 feet; beam engine, horse-power per stroke from water raised 27, from indicator 32·5; ordinary strokes per minute 6½, maximum 9; lift 192 feet.
These three pumps pump tunnel water only—the drainage from the 5-foot culvert—and in dry weather one of them working at the ordinary rate is sufficient.
At the 29-foot Shaft, Sudbrook, three 35-inch plungers, with 9-foot stroke, each raising 376 gallons per stroke (the three 1,128 gallons), and three 34-inch plungers, each raising 355 gallons per stroke (the three 1,065 gallons)—the engines have already been described; steam cylinders 70 inches diameter, 10-foot stroke; horse-power per stroke from water raised, plunger-pump 20, bucket 19; ordinary strokes per minute 7 and 8½, maximum 10 and 12; lift 167 feet. In dry weather only three of these pumps work at one time; one plunger-pump, at least, is among the number, on account of the fresh-water lift.
At 5 miles 4 chains, one 35-inch plunger, with 9-foot stroke, raising 376 gallons per stroke, and one 34-inch bucket, 9-foot stroke, raising 355 gallons per stroke; the steam cylinders 65 inches diameter, 10-foot stroke; beam engine, horse-power from water lifted 15·30 and 14·4; ordinary strokes per minute 7½, maximum plunger 10 and bucket 12; lift 134 feet. Generally only one pump works at a time.
At Benacre, two 20-inch plungers, with 6-foot stroke, raising 82 gallons per stroke, or 164 gallons the two; the steam cylinders 22 inches diameter, stroke same as pump; Bull engines, horse-power per stroke from water lifted 1·32; ordinary strokes per minute 9, maximum 18; lift 56 feet. These pumps drain the cutting, and do not work in summer, the water being raised from 5 miles 4 chains.
On the Gloucestershire side, at Sea-wall Shaft, one 29-inch plunger and one 29-inch bucket, 9-foot stroke, each raising 258 gallons per stroke; steam cylinders 41 inches diameter, 10-foot stroke; beam engines, horsepower per stroke from water lifted 7·66 each pump; ordinary strokes per minute average 5½, maximum plunger 10, bucket 12; lift 98 feet. These pumps take water from cutting and a length of tunnel; as a rule, one only works at a time.
Where the horse-power from water raised only is given, there were no indicators on the engines. The indicated horse-power will be about 25 per cent, more than the actual horse-power.
The deliveries of the pumps given above are theoretical The actual deliveries will be about 20 per cent. less. The pumps, therefore, are capable of raising about 6 million gallons per day, as stated in Colonel Rich’s report.