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HYDRAULIC POWER
Syllabus Statements
Archimedes’ Principle
Pascal’s Principle
Hydrostatic Pressure
Outcomes
This unit of work addresses aspects of the following syllabus outcomes:
H2.2 analyses and synthesises engineering applications in specific fields and reports on the importance of these to society.
H3.1 demonstrates proficiency in the use of mathematical methods to analyse and solve problems of engineering practice
H4.1 investigates the extent of technological change in engineering.
H4.2 applies knowledge of history and technological change to engineering based problems
H4.3 appreciates social, environmental and cultural implications of technological change in engineering and applies them to the analysis of specific problems.
Extract from Stage 6 Industrial Technology Syllabus © Board of Studies NSW 1999.
Fluid Mechanics - People and Principles
We cannot really study the operation of machines or devices that involve fluids without first understanding the fundamental principles relating to the behaviour of fluids.
Historically, three men set down the principles of fluid mechanics that form the basis of hydraulics today. The first of these was Archimedes who lived in the second century BC. Read about his life and contribution to engineering and mathematics by visiting the web site at http://web01.shu.edu/projects/reals/history/archimed.html 
, a history of Archimedes (287-212BC).
Visit the following web site to read a statement of Archimedes’ principle http://www.infoplease.com/ce6/sci/A0804583.html and explain how a submarine floating on the surface can be made to dive.
The second person to study and quantify the behaviour of fluids was Blaise Pascal. He lived in the 17th century AD, and you can read about his life and contribution to society at the following web site http://en.wikipedia.org/wiki/Blaise_Pascal , a history of Blaise Pascal (1623-1662)
Visit the following web site and use Pascal’s principle to explain how hydraulic brakes work in a motor vehicle http://webphysics.davidson.edu/physlet_resources/bu_semester1/c23_pressure_pascal.html .
Another concept developed by Pascal was that of hydrostatic pressure. Visit the web site http://en.wikipedia.org/wiki/Pressure#Hydrostatic_pressure_.28head_pressure.29 to gain an understanding of hydrostatic pressure. This concept will be focussed on in the next section of this unit of work.
The third important person to contribute to the study of fluids was Jacob Bernouli A summary of Jacob’s life can be found at http://www-history.mcs.st-andrews.ac.uk/Biographies/Bernoulli_Jacob.html , a history of Jacob Bernouli (1654-1705).
Visit the web site http://home.earthlink.net/~mmc1919/venturi.html to view an explanation and demonstration of Bernouli’s principle.
Hydraulic Power
Coal had been a source of energy since the early days in colonial Sydney, mainly as a source of heat and to raise steam in industrial boilers. Town Gas, produced from coal, was introduced in the early nineteenth century primarily as a source of light for street lamps and homes.
While the application of steam to produce mechanical power (linear and rotative) was reaching its peak in the middle of the nineteenth century, the development of gas powered engines was still on the horizon. Petroleum was relatively unknown, and whilst experiments with electricity were producing new applications, industrial power from electricity was still far in the future.
The smoke and smog being produced from hundreds of small steam boiler plants was beginning to choke big cities and something had to be done. The solution for many big cities such as London, Boston, Melbourne and Sydney was the development of centralised steam powered pumps producing high pressure water which was reticulated throughout the city to power cranes, lifts and other machinery.
Read more about Why Cities needed Hydraulic Power
Read more about Hydraulic power in Sydney
Hydraulic Power – How did the system work?
Most students will recognise that water under pressure (hydrostatic pressure) can be used to do useful work.
The essentials of a hydraulic power system are the water supply (dam), high pressure pumps, an accumulator, and a reticulation system as shown in the following diagram
Diagram of the Sydney Hydraulic System
1. The water supply – this was usually from a dam or the city’s own water supply system. Water was pumped from the supply to the pumping station at low pressure.
2. High pressure pumps – these were initially steam driven, later electrically driven, reciprocating pumps capable of pressures of up to 5 MPa. They pumped water into the accumulator.
HP Water Pump at Walsh Bay, Sydney
3. The accumulator – this is probably the most important component in the system as it developed the high pressure and allowed the storage of quantities of high pressure water for use throughout the city. The accumulator consisted of a long fixed cylinder with a vertical piston in it. Fixed to the piston was a large weight. Water from the pumps was forced into the cylinder thus forcing the piston to rise against the weight.
Accumulator – Walsh Bay, Sydney
If the mass on the accumulator piston was 102 tonne, and the piston diameter was 508 mm, calculate the water pressure,
4. T he reticulation system – this comprised a series of mains and sub-main cast iron pipes with control valves outside the customer’s premises. In Sydney the system covered roughly the area between Woollomoloo, Pyrmont and Ultimo.
Valve cover outside 160 Clarence St, Sydney
At the Customer’s end
Typical applications for hydraulic power in Sydney were wharf cranes, wool presses, goods/bullion lifts, passenger lifts, and hydraulic machinery.
If we use a passenger lift in a department store as an example, two main possibilities existed – a direct acting system, or an indirect acting system.
In a direct acting system the passenger car rests on top of a piston in a cylinder connected to the high pressure water mains (refer to the diagram below). Water is let into a valve control system from ropes in the lift cage.
Direct Acting Hydraulic Passenger Lift c.1900
Note – the cylinder extends below the ground the same distance as the length of the piston.
As the high pressure water fills the cylinder it pushes the piston up, thus raising the cage. When at the required floor in the building, the operator closed the valve to stop the lift. To go down, another valve was opened that allowed the water in the cylinder to exhaust into a drain.
Some smaller hydraulic lift systems recirculated the exhaust water back to the pumps.
The speed of these lifts was quite low and limited to the rate of water supply.
Analyse a typical lift system and describe some of its limitations.
If the lift in the diagram above serviced three floors at 3 m each, the piston was 127 mm in diameter and the pressure 5 MPa. What is the maximum load that can be carried?
In an indirect system the piston is attached to a pulley system arranged as a “block and tackle”. This increases the speed of the lift and the overall height capability, but limits the maximum load.
Indirect Hydraulic Lift System
In the system shown in the diagram above lets assume there are three pulleys on the fixed sheave and three pulleys on the travelling sheave. The pulley system has a velocity ratio of six. In practical systems it was possible to use 2 - 5 pulley block and tackle giving a velocity ratio from 4 -10.
Another advantage of the indirect system is that the cylinder can be either horizontal or vertical.
Let’s see how the indirect system worked. We have a piston of 127 mm diameter, and we will assume that the piston travels 3 m in one minute. So a direct system lift would rise 9 m floors in three minutes. Its load would be limited to 63 kN (activity 6).
In the indirect system if the piston moves 1 m then the travelling sheave will move 1 m, but the hoisting rope will actually move six metres. The velocity ratio of the block and tackle is 6.
VR = distance the load moves / distance the effort moves
load (lift) distance is 6 m / effort (piston) moves 1 m
VR = 6 / 1
= 6
The lift will cover the 9 m in a half a minute.
However, what is the effect of the indirect system on the maximum load able to be carried in the lift.
The efficiency of a perfect machine is given by MA / VR = 1.
Therefore the block and tackle connected to the piston has a mechanical advantage of 1 / VR.
MA = 1 / VR = load / effort
load = effort / VR
= 63000 / 6
10500 N or 10.5 kN.
Therefore, using the indirect system the speed of the lift is increased, the lift can service taller buildings, BUT the load is restricted
Why was grey cast iron the main material used for the production of cylinders for hydraulic systems, and why were the cylinder walls relatively thick?
Hydraulic Passenger Lift. 1 Kent St., Sydney.
Without the water based hydraulic system the height restriction on ‘modern’ buildings would have lasted well into the 20th century until electrically powered lifts became common thus giving rise to the skyscraper.
Hydraulic power, using oil based hydraulics is used in many application to power machinery and equipment. In fact some smaller lifts being installed at suburban railway stations in Sydney are hydraulically powered using a direct acting system. Height limitations have been overcome using multi-stage concentric pistons. An example of such a system is at Wynyard and Town Hall.
Hydraulic Lift, Woolloomooloo Finger Wharf.
Hydraulic Power – Why did Cities need Hydraulic Power?
By the 1870s in Sydney, NSW the predominant sources of energy for industry were coal, and gas. Coal had been a source of energy since the early days of the colony, mainly as a source of heat and to raise steam in industrial boilers. Gas was introduced in 1841 by the Australian Gas Light Co (AGL) primarily as a source of light for streetlamps and homes.
While the application of steam to produce mechanical power (linear and rotative) was reaching its peak in the middle of the nineteenth century, the development of gas powered engines was still on the horizon. Petroleum was relatively unknown, and whilst experiments with electricity were producing new applications, industrial power from electricity was still far in the future.
The continued application of steam posed two significant problems to the industrialists (i) it could not be readily reticulated over large distances and (ii) it was polluting the town as John Birmingham in his book ‘Leviathan’ recorded - thousands of furnaces burnt millions of tons of wood and coal bringing with it the choking smog.
What was needed was a new, readily reticulated, reliable power source from a centralised supply. As pointed out above, gas could be reticulated but the engines for it to power did not exist. Steam could be reticulated but only to a limited extent as in hospitals.
The solutions available at the time were centralised power stations producing compressed air (pneumatics), or water power (hydraulics) with either power source being reticulated throughout the streets of the town. Each could be easily controlled and used in machines to produce linear or rotative mechanical power. Either of these solutions would see a significant reduction in the number of small steam boilers and hence a reduction in pollution and a theoretical rise in efficiency.
Experiments using hydraulics to power machinery had been carried out as early as 1802 in the United Kingdom. By the mid 1800s it was possible to supply water at pressures from 700 psi (4.8 MPa) upward over distances of up to 15 miles (24 km). The first public hydraulic power system commenced operation in Hull (UK) in 1876 and in London by 1884.
By 1878, only 2 years after the commencement of the Hull system, Edward Moriarty had produced a hydraulic system for the Newcastle dockyard (Bullock Island) in Australia. On 19 March 1878, the first shipment of coal loaded by hydraulic crane left Newcastle aboard the ship Downiemount. Subsequent systems in Australia commenced in Melbourne in 1889 and Sydney in 1891.
The public hydraulic power system in Sydney commenced in 1891 and closed down in 1975. It was used to power cranes on the wharves, public and goods lifts in department stores and commercial buildings, orchestra lifts in theatres such as the State Theatre, wool presses, bullion lifts in banks and a variety of machinery such as forges. Hydraulic lifts tended to be quite slow in operation and it is not surprising that faster electric motor driven lifts quickly replaced the water powered ones. Hydraulic lifts also had height limitations due to the limits on cylinder/piston combinations.
The Sydney and Suburban Hydraulic Power Co.
The government of NSW passed an Act of Parliament in 1888 authorising the establishment of an hydraulic power company to serve the business district. It commenced supply of power in January 1891 with Mr. George Swinburne as company engineer. By 1894 about 200 machines were connected to the system. Gradually the system expanded to cover roughly the area from Pyrmont to Woolloomooloo and south to Broadway. The system supplied power for dock cranes, whips, presses, doors, and passenger and goods lifts in department stores and commercial buildings.
The central powerhouse for the Sydney system still stands near the Entertainment Centre in Pier St.
SHPCo Pier St. Pumphouse
It is not known how many consumers were connected to the SHPC system at its peak, however, it was reported that by 1894 there were 149 lifts, 22 whips, 7 wool presses, 20 dock cranes and 2 motors connected – and this was just 3 years after commencing supply! The NSW Dept. of Labour and Industry reported that in 1903 it had registered 522 hydraulic lifts, and only 3 electric lifts, by 1919 this had risen to 2369 lifts and whips in the metropolitan area, most of which were operated hydraulically. It is also reported that SHPC had laid some 50 mile (80 km) of supply pipe throughout Sydney CBD at its closure.
Records suggest that the peak period for hydraulic power, under threat from diesel and electric power, was in the mid 1930s and that the profit and loss break-even point was reached in 1965. By 1968 there were no more than 150 customers on the system which ceased operation in 1975.
It is interesting to note that the Sydney system lasted from 1891 until 1975, and was the longest lasting system in the world.
Hydraulic whip on Campbell’s Stores, The Rocks, Sydney.
A number of SHPC valve covers still exist in Sydney streets today, particularly in Kent and Clarence Sts. You can see remains of the system on Campbell’s Stores, and Argyle Stores in the Rocks, and in the atrium of No.1 Kent St.
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