engineering

Hydraulics

Hydraulics is a engineering topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Hydraulics rather than just read about it. In short: Hydraulics (from Ancient Greek ὕδωρ (húdōr) 'water' and αὐλός (aulós) 'pipe') is a technology and applied science using engineering, chemistry, and other sciences involving the mechanical properties and use of liquids. Rooted in fluid mechanics, hydraulics is used to govern the use of energy via pressurized liquids.

Key takeaways

Hydraulics belongs to engineering; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Hydraulics to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Hydraulics from memory before moving on to harder problems.

Reference excerpt

Hydraulics (from Ancient Greek ὕδωρ (húdōr) 'water' and αὐλός (aulós) 'pipe') is a technology and applied science using engineering, chemistry, and other sciences involving the mechanical properties and use of liquids. Rooted in fluid mechanics, hydraulics is used to govern the use of energy via pressurized liquids. It has been part of human history since ancient times. Hydraulic topics range through some parts of science and most engineering modules. Free surface hydraulics is the branch of hydraulics dealing with free surface flow, such as occurring in rivers, canals, lakes, estuaries and seas. Its sub-field, open-channel flow, studies the flow in open channels.

Overview Fluid mechanics provides the theoretical foundation for hydraulics, which focuses on applied engineering using the properties of fluids. In its fluid power applications, hydraulics is used for the generation, control, and transmission of power by the use of pressurized liquids. Hydraulic topics range through some parts of science and most of engineering modules, and they cover concepts such as pipe flow, dam design, fluidics, and fluid control circuitry. The principles of hydraulics are naturally in use in the human body within the vascular system and erectile tissue. Free surface hydraulics is the branch of hydraulics dealing with free surface flow, such as occurring in rivers, canals, lakes, estuaries, and seas. Its sub-field open-channel flow studies the flow in open channels. At a very basic level, hydraulics is the liquid counterpart of pneumatics, which concerns gases.

Early history

Early uses of water power date back to Mesopotamia and ancient Egypt, where irrigation has been used since the 6th millennium BC and water clocks have been used since the early 2nd millennium BC. Other early examples of water power include the Qanat system in ancient Persia, the Turpan water system in ancient Central Asia, and the Piedras Bolas aqueduct in ancient Mexico.

Maya The Maya at Palenque (in modern-day Chiapas, Mexico) engineered the first known pressurized water system in the Americas. By constructing a subterranean aqueduct (the Piedras Bolas aqueduct) that narrowed significantly at the downstream end, they utilized hydraulic principles to create water pressure capable of shooting water upwards to a height of 6 meters (20 ft). This system was likely used for fountains or sanitary purposes, operating without the need for mechanical pumps.

Persian Empire and Urartu In the Persian Empire or previous entities in Persia, the Persians constructed an intricate system of water mills, canals and dams known as the Shushtar Historical Hydraulic System. The project, commenced by Achaemenid king Darius the Great and finished by a group of Roman engineers captured by Sassanian king Shapur I, has been referred to by UNESCO as "a masterpiece of creative genius". They were also the inventors of the Qanat, an underground aqueduct, around the 9th century BC. Several of Iran's large, ancient gardens were irrigated thanks to Qanats. The Qanat spread to neighboring areas, including the Armenian highlands. There, starting in the early 8th century BC, the Kingdom of Urartu undertook significant hydraulic works, such as the Menua canal. The earliest evidence of water wheels and watermills dates back to the ancient Near East in the 4th century BC, specifically in the Persian Empire before 350 BC in the regions of Iraq, Iran, and Egypt.

China In ancient China there were Sunshu Ao (6th century BC), Ximen Bao (5th century BC), Du Shi (circa 31 AD), Zhang Heng (78 – 139 AD), and Ma Jun (200 – 265 AD), while medieval China had Su Song (1020 – 1101 AD) and Shen Kuo (1031–1095). Du Shi employed a waterwheel to power the bellows of a blast furnace producing cast iron. Zhang Heng was the first to employ hydraulics to provide motive power in rotating an armillary sphere for astronomical observation.

Sri Lanka

In ancient Sri Lanka, hydraulics were widely used in the ancient kingdoms of Anuradhapura and Polonnaruwa. The discovery of the principle of the valve tower, or valve pit, (Bisokotuwa in Sinhalese) for regulating the escape of water is credited to ingenuity more than 2,000 years ago. By the first century AD, several large-scale irrigation works had been completed. Macro- and micro-hydraulics to provide for domestic horticultural and agricultural needs, surface drainage and erosion control, ornamental and recreational water courses and retaining structures and also cooling systems were in place in Sigiriya, Sri Lanka. The citadel on the massive rock at the site includes cisterns for collecting water. Large ancient reservoirs of Sri Lanka are Kalawewa (King Dhatusena), Parakrama Samudra (King Parakrama Bahu), Tisa Wewa (King Dutugamunu), and Minneriya (King Mahasen).

Greco-Roman world In Ancient Greece, the Greeks constructed sophisticated water and hydraulic power systems. An example is a construction by Eupalinos, under a public contract, of a watering channel for Samos, the Tunnel of Eupalinos. An early example of the usage of a hydraulic wheel, likely the earliest in Europe, is the Perachora wheel (3rd century BC). In Greco-Roman Egypt, the construction of the first hydraulic machine automata by Ctesibius (flourished c. 270 BC) and Hero of Alexandria (c. 10 – 80 AD) is notable. Hero describes several working machines using hydraulic power, such as the force pump, which is known from many Roman sites as having been used for raising water and in fire engines.

In the Roman Empire, different hydraulic applications were developed, including public water supplies, innumerable aqueducts, power using watermills and hydraulic mining. They were among the first to make use of the siphon to carry water across valleys, and used hushing on a large scale to prospect for and then extract metal ores. They used lead widely in plumbing systems for domestic and public supply, such as feeding thermae. Hydraulic mining was used in the gold-fields of northern Spain, which was conquered by Augustus in 25 BC. The alluvial gold mine of Las Medulas was one of the largest of their mines. At least seven long aqueducts worked it, and the water streams were used to erode the soft deposits, and then wash the tailings for the valuable gold content.

… excerpt ends here. Continue reading the full article.

Illustrations

Worked examples

Example 1 — a first encounter with Hydraulics

Start with the simplest possible case. Write down what Hydraulics claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In engineering, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Hydraulics before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Hydraulics ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Hydraulics

In research: Hydraulics appears in engineering research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Hydraulics in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Hydraulics is common in secondary-school and first-year university syllabi. It links to neighbouring topics Ancient inventions, Hellenistic engineering, Hydraulic engineering, so understanding it makes those chapters shorter.
In everyday life: Look for Hydraulics outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Hydraulics in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Hydraulics means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Hydraulics out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Hydraulics in simple terms?

Why does Hydraulics matter?

Because it connects several engineering ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Hydraulics?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Hydraulics.