# Hydraulics Book Excerpt

Also see hydraulic power.

Excerpt from http://books.google.com/books?id=emYJAAAAIAAJ&pg=PA233&dq=hydraulic+accumulator&as_brr=1#PPA240,M1

Capacity of Accumulators. 235

overcome by a pressure of 12^ Ibs. per square inch, 1 per cent, of the energy being wasted in charging, and 1 per cent, in discharging, or the efficiency of the accumulator as a store-house for energy is 98 per

cent.

Storage Capacity Of Accumulators.

The energy stored when the weight W Ibs. is at the top of its stroke of h feet is W h ft.-Ibs.

If the accumulator discharges at / Ibs. per square inch, its usual storage is 62-4 X 2-3/A/ / ft.-Ibs., A being the area of the ram

cross-section in square feet, and its capacity ^ -* X. p \ k

33,000 X 60

< horse-power hours, nearly.

13,80° An accumulator performs several useful functions. Thus it acts

as a store-house for energy, but is useful more in the nature of a fly-wheel to level up inequalities of supply and demand than to provide a large store. Thus each large accumulator of the London Hydraulic Power Company stores 106 X 2240 X 23 = 5,461,120 ft.-Ibs., but since 1 horse-power for an hour requires 1,980,000 ft.- Ibs., the accumulator only has a storage capacity of about 2 - 8 horsepower hours. It can, however, give out a great power for a short time, say, 160 horse-power for one minute. Compare even a number of these accumulators with a storage reservoir, such as that at Zurich, which contains 353,000 cubic feet at an elevation of 475 feet above the motors, having therefore a capacity of 5284 horse-power hours.

The accumulator acts as a pressure regulator, keeping the pressure in the mains constant and nearly equal (in Ibs. per square inch) to

W

—, where a is the area of the ram in square inches, W being in Ibs. &

It provides the elastic arrangement necessary in such a system, for if all the machines in the system stop suddenly, the pumps merely raise the accumulator weight, whereas if no such arrangement were provided, something must be broken.

It also has the fourth use of providing an automatic system, the pumps being controlled by the accumulator as already described.

Loading...Loading...Capacity of Accumulators. 235

overcome by a pressure of 12^ Ibs. per square inch, 1 per cent, of the energy being wasted in charging, and 1 per cent, in discharging, or the efficiency of the accumulator as a store-house for energy is 98 per

cent.

Storage Capacity Of Accumulators.

The energy stored when the weight W Ibs. is at the top of its stroke of h feet is W h ft.-Ibs.

If the accumulator discharges at / Ibs. per square inch, its usual storage is 62-4 X 2-3/A/ / ft.-Ibs., A being the area of the ram

cross-section in square feet, and its capacity ^ -* X. p \ k

33,000 X 60

< horse-power hours, nearly.

13,80° An accumulator performs several useful functions. Thus it acts

as a store-house for energy, but is useful more in the nature of a fly-wheel to level up inequalities of supply and demand than to provide a large store. Thus each large accumulator of the London Hydraulic Power Company stores 106 X 2240 X 23 = 5,461,120 ft.-Ibs., but since 1 horse-power for an hour requires 1,980,000 ft.- Ibs., the accumulator only has a storage capacity of about 2 - 8 horsepower hours. It can, however, give out a great power for a short time, say, 160 horse-power for one minute. Compare even a number of these accumulators with a storage reservoir, such as that at Zurich, which contains 353,000 cubic feet at an elevation of 475 feet above the motors, having therefore a capacity of 5284 horse-power hours.

The accumulator acts as a pressure regulator, keeping the pressure in the mains constant and nearly equal (in Ibs. per square inch) to

W

—, where a is the area of the ram in square inches, W being in Ibs. &

It provides the elastic arrangement necessary in such a system, for if all the machines in the system stop suddenly, the pumps merely raise the accumulator weight, whereas if no such arrangement were provided, something must be broken.

It also has the fourth use of providing an automatic system, the pumps being controlled by the accumulator as already described.

Loading...Loading...Capacity of Accumulators. 235

overcome by a pressure of 12^ Ibs. per square inch, 1 per cent, of the energy being wasted in charging, and 1 per cent, in discharging, or the efficiency of the accumulator as a store-house for energy is 98 per

cent.

Storage Capacity Of Accumulators.

The energy stored when the weight W Ibs. is at the top of its stroke of h feet is W h ft.-Ibs.

If the accumulator discharges at / Ibs. per square inch, its usual storage is 62-4 X 2-3/A/ / ft.-Ibs., A being the area of the ram

cross-section in square feet, and its capacity ^ -* X. p \ k

33,000 X 60

< horse-power hours, nearly.

13,80° An accumulator performs several useful functions. Thus it acts

as a store-house for energy, but is useful more in the nature of a fly-wheel to level up inequalities of supply and demand than to provide a large store. Thus each large accumulator of the London Hydraulic Power Company stores 106 X 2240 X 23 = 5,461,120 ft.-Ibs., but since 1 horse-power for an hour requires 1,980,000 ft.- Ibs., the accumulator only has a storage capacity of about 2 - 8 horsepower hours. It can, however, give out a great power for a short time, say, 160 horse-power for one minute. Compare even a number of these accumulators with a storage reservoir, such as that at Zurich, which contains 353,000 cubic feet at an elevation of 475 feet above the motors, having therefore a capacity of 5284 horse-power hours.

The accumulator acts as a pressure regulator, keeping the pressure in the mains constant and nearly equal (in Ibs. per square inch) to

W

—, where a is the area of the ram in square inches, W being in Ibs. &

It provides the elastic arrangement necessary in such a system, for if all the machines in the system stop suddenly, the pumps merely raise the accumulator weight, whereas if no such arrangement were provided, something must be broken.

It also has the fourth use of providing an automatic system, the pumps being controlled by the accumulator as already described.

Loading...Loading...Capacity of Accumulators. 235

cent.

Storage Capacity Of Accumulators.

The energy stored when the weight W Ibs. is at the top of its stroke of h feet is W h ft.-Ibs.

cross-section in square feet, and its capacity ^ -* X. p \ k

33,000 X 60

< horse-power hours, nearly.

13,80° An accumulator performs several useful functions. Thus it acts

W

—, where a is the area of the ram in square inches, W being in Ibs. &

Loading...Loading...Capacity of Accumulators. 235

cent.

Storage Capacity Of Accumulators.

The energy stored when the weight W Ibs. is at the top of its stroke of h feet is W h ft.-Ibs.

cross-section in square feet, and its capacity ^ -* X. p \ k

33,000 X 60

< horse-power hours, nearly.

13,80° An accumulator performs several useful functions. Thus it acts

W

—, where a is the area of the ram in square inches, W being in Ibs. &

Engines.

In describing very briefly some of the details of the system which has been so successfully adopted in London, the engines, pumps and boilers may be first referred to. Figs. 160 and 161 show a side and Loading...Loading...front elevation of Mr. Ellington's engines, made by the Hydraulic Engineering Co., of Chester. Each engine has three inverted cylinders, the piston of each cylinder working directly a single-acting pump.

>

Fig. 160 balance of reciprocating parts. The high-pressure cylinder has a variable expansion valve on the back of the main slide, adjustable whilst the engine is .running, thus enabling the point of cut-off to be varied to suit the work and steam pressure.

All the cylinders are steam-jacketed arid provided with connections which allow the water of condensation to be returned to the boilers by gravitation. (The student is not to suppose that water can usually be forced into the boilers by gravitation—it is, however, in this case, as both the steam and return water pipes are under the boiler pressure.)

The cylinders are carried on four steel columns at the front, and three cast-iron columns at the back, incorporated with and forming part of the condenser. The pumps are attached to the cast-iron columns and stayed to the cylinders by steel bars, which also act as front guides for the engine cross-heads.

The air, circulating, and feed pumps are placed behind the condenser, and worked from the piston of the intermediate cylinder by rocking levers and links.

The engine is controlled by a high-speed governor; automatic gear is also provided by which the engine is controlled by the accumulator, somewhat in the way already described.

At a nine-hours' trial of a set of these engines at the Wapping station, with high-pressure cylinder 15 inches, intermediate cylinder 22 inches, and low-pressure 36 inches in diameter, all 2 feet stroke, 160,880 gallons of water were pumped against an accumulator pressure of 7 95 Ibs. per square inch. The indicated horse-power of the engines was 206'55, steam consumption 15-26 Ibs. per horse-power per hour, and coal consumption 1 - 49 Ibs. per indicated horse-power per hour.

Of this steam consumption 1'16 Ibs. per indicated horse-power per hour were accounted for by steam-pipe condensation and loss. The coal used contained 8J per cent, of clinker and ash.

The London Hydraulic Power Company have nineteen sets of engines of this type at work. They are very compact, and it will be seen from the results given above that the efficiency is high.

Another type of engine-—made by the same firm—is shown in elevation and plan in Figs. 162 and 163, and is the engine adopted at the Hull Docks to supply water for the mains of the Dock machinery, the pressure being 800 Ibs. per square inch. This, as will be seen, is a horizontal engine with two high-pressure cylinders 20 inches in diameter, and two low-pressure cylinders 38 inches in diameter, arranged tandem fashion, with pumps of the piston and