Nature.

THE DISTRIBUTION OF HYDRAULIC POWER IN LONDON.

At a recent meeting of the Institution of Civil Engineers, a paper on the above subject was read by Mr. Edward Bayzand Ellington, M. Inst. C. E. The author observed that water power was no new force, but that, as formerly understood, it was limited in its application to systems of mechanism suitable for the low pressures found in nature. The effects obtained by the use of high pressure were so different in degree from all previous experience, that a new name was needed, and had been found in the term "hydraulic power." Bramah's genius produced the hydraulic press, and he clearly foresaw the future development and great capabilities of his system; but it was reserved for Lord Armstrong to work out and superintend the intricate details that had to be developed before the system could be made fully serviceable. The public supply of hydraulic power in London constituted the latest development of this system. The hydraulic power was supplied through mains charged by pumping at a pressure of 700 lb. per square inch. The first and largest pumping station had been erected on a site known as Falcon Wharf, about 200 yards east of Blackfriars Bridge. The engine house at present contained four sets of pumping engines, each set being capable of exerting 200 I. H. P.

The engines were vertical compound, of a type comprising the advantages of a three-throw pump with direct connection between the pump plungers and the steam pistons. Each set of engines would deliver 240 gallons of water per minute into the accumulators at 750 lb. pressure per square in. at a piston speed of 200 ft. per minute. This was the normal speed of working; but, when required, they could be worked at 250 ft. per minute, the maximum delivery being 300 gallons per minute. The condensing water was obtained from storage tanks over the engine house, and was returned by circulating pumps to one or other of those tanks. The water delivered into the mains was maintained all the year round at temperatures of between 60° and 85°. The boilers were of the double flued Lancashire type, and were made of steel. All were fitted with Vicars' mechanical stokers. At the back of the boilers was a Green's economizer, consisting of ninety-six tubes. The economizer and the stoker gear and worm were driven by a Brotherhood three cylinder hydraulic engine. The reservoir of power consisted of accumulators. The accumulators at the pumping station were two in number, each having a ram 20 in. in diameter and 23 ft. stroke.

The weight cases were of wrought iron, and were filled with iron slag. The total weight of the case and load on each ram was approximately 106 tons, corresponding to a pressure of 750 lb. per square in. The storage tanks formed the roofs for the engine and boiler houses. The water for the power supply was obtained from the river Thames, and was pumped into the tank over the engines. The water passed through the filtering apparatus by gravity into the filtered water tank over the boiler house, which was 7 ft. below the level of the unfiltered water tank. The filters consisted of cast iron cylinders, and each contained a movable perforated piston and a perforated diaphragm, between which was introduced a quantity of broken sponge; the sponge was compressed by means of hydraulic pressure from the mains. The delivery of power water from the Falcon Wharf pumping station was through four 6 in. mains. The most distant point of the mains from the accumulators was at the west end of Victoria Street, and was 5,320 yards, or just over three miles. To provide for all frictional loss in the pipes and valves, the accumulators had been loaded to 750 lb., the stated pressure supplied being 700 lb. per square in. The total length of the mains at present laid was nearly twenty-seven miles. The mains were laid in circuit, and there were stop valves at about every 400 yards, so that any such section of main could be isolated.

The method employed for detecting leakage was based upon an automatic record of the number of gallons delivered into the mains, and in cases of abnormal increase during the night, if found to arise during the early hours of the morning, the mains were tested. The power water used was invariably registered through meters on the exhaust pipes from the machines, and from the meters passed to the drains. There was a sliding scale of charges from 8s. to 2s. per 1,000 gallons at 700 lb. pressure per square inch, designed to meet, as nearly as possible, the variable conditions and requirements of consumers. The more continuous the use, the lower the charges. The scale was intended chiefly for intermittently acting machinery, and experience had fully proved that these rates were sufficiently low to effect a large saving to the consumer in almost all cases, whether for a large or a small plant. The author believed any idea of supplying power from a central source at rates much below these to be chimerical. The practical efficiency of the hydraulic system might be fixed at from 50 to 60 per cent. of the power developed at the central station. No other method of transmission would, he thought, show a better result; and the general convenience and simplicity of the hydraulic system were such that its use would hardly be affected, even if there were no direct economy in the cost of working.

In addition to the general supply of hydraulic power, in the City and adjoining districts, to the six hundred and fifty machines at present worked, a new departure had been taken by the application of hydraulic power to an estate at Kensington Court—the name given to an area of about seven acres opposite Kensington Gardens. Seventy houses and dwellings were to be built on this estate, of which thirty had been already erected. Each house was fitted with a hydraulic lift, taking the place of a back staircase, and the power supply was provided on the estate expressly for working these lifts. The driven machinery was of as great importance to an economical and satisfactory result as

the distributing plant, but this obvious fact was not always understood. General regulations had been prepared by the author, defining the conditions to be observed by manufacturers in fitting up machinery for connection to the power mains.

They were intended to secure safety, and an efficient registration of the quantity of power used; but they left the question of the economy and of the efficiency of the machines to be settled between the consumers and the makers. In London more lifts were working from the mains and more power was used by them than by any other description of machinery. The number of all classes at present at work was over four hundred. The principal types in use were fully described. In some cases there had been, by adopting the public supply, a saving in the cost of working of about 30 per cent., as compared with the steam pumping plant previously in use.

Lifts were now becoming so general, and the number of persons who used them was so great, that the author considered it necessary to urge the importance of securing the greatest possible safety in their construction, by the general adoption of the simple ram. Suspended lifts depended on the sound condition of the ropes or chains from which the cages hung. As they became worn and unreliable after a short period, it was usual to add safety appliances to stop the fall of the cage in case of breakage of the suspending ropes; but they could not be expected to act under all circumstances. As an indication of the important part which lifts occupied in a modern hotel, it might be mentioned that at the Hotel Metropole there were, including the two passenger lifts and that for the passengers' luggage, no less than seventeen hydraulic lifts in use day and night, while the work done represented about 2,000 tons lifted 40 ft. in this time. The next largest use of the power was for working hydraulic cranes and hoists of various kinds along the