A hydraulic press is a machine using a hydraulic cylinder to generate a compressive force. It uses the hydraulic equivalent of a mechanical lever, and was also known as a Bramah press after the inventor, Joseph Bramah, of England. He invented and was issued a patent on this press in 1795. As Bramah (who is also known for his development of the flush toilet) installed toilets, he studied the existing literature on the motion of fluids and put this knowledge into the development of the press.
Joseph Bramah (13 April 1748 – 9 December 1814), born Stainborough Lane Farm, Stainborough, Barnsley Yorkshire, England, was an inventor and locksmith. Along with William George Armstrong, he can be considered one of the two fathers of hydraulic engineering.
He was educated at the local school in Silkstone and on leaving school he was apprenticed to a local carpenter. On completing his apprenticeship he moved to London, where he started work as a cabinet-maker. In 1783 he married Mary Lawton of Mapplewell, nearBarnsley, and the couple set up home in London.
He found that the current model being installed in London houses had a tendency to freeze in cold weather. Although it was Allen who improved the design by replacing the usual slide valve with a hinged flap that sealed the bottom of the bowl, Bramah obtained the patent for it in 1778, and began making toilets at a workshop in Denmark Street, St Giles. The design was a success and production continued well into the 19th century.
His original water closets are still working in Osbourne House, Queen Victoria's home on the Isle of Wight.
The hydraulic press depends on Pascal's principle: the pressure throughout a closed system is constant. One part of the system is a piston acting as a pump, with a modest mechanical force acting on a small cross-sectional area; the other part is a piston with a larger area which generates a correspondingly large mechanical force. Only small-diameter tubing (which more easily resists pressure) is needed if the pump is separated from the press cylinder.
Pascal's law: Pressure on a confined fluid is transmitted undiminished and acts with equal force on equal areas and at 90 degrees to the container wall. A fluid, such as oil, is displaced when either piston is pushed inward. The small piston, for a given distance of movement, displaces a smaller amount of volume than the large piston, which is proportional to the ratio of areas of the heads of the pistons.
Therefore, the small piston must be moved a large distance to get the large piston to move significantly. The distance the large piston will move is the distance that the small piston is moved divided by the ratio of the areas of the heads of the pistons. This is how energy, in the form of work in this case, is conserved and the Law of Conservation of Energy is satisfied. Work is force applied over a distance, and since the force is increased on the larger piston, the distance the force is applied over must be decreased.
Bramah's basic idea is also exploited in hydroforming.
Hydraulic presses are commonly used for forging, clinching, moulding, blanking, punching, deep drawing, and metal forming operations.
Bramah designed a lock of his own, receiving a patent for it in 1784. The locks produced by his company were famed for their resistance to lock picking and tampering, and the company famously had a "Challenge Lock" displayed in the window of their London shop from 1790 mounted on a board containing the inscription:
The artist who can make an instrument that will pick or open this lock shall receive 200 guineas the moment it is produced.
The challenge stood for over 67 years until, at the Great Exhibition of 1851, the American locksmith Alfred Charles Hobbs was able to open the lock and, following some argument about the circumstances under which he had opened it, was awarded the prize. Hobbs' attempt required some 51 hours, spread over 16 days. The Challenge Lock is in the Science Museum in London. An examination of the lock shows that it has been rebuilt since Hobbs picked it. Originally it had 18 iron slides and 1 central spring; it now has 13 steel slides, each with its own spring.
Bramah received a second patent for a lock design in 1798. He was a very prolific inventor, though not all of his inventions were as important as his hydraulic press. They included: a beer engine (1797), a planing machine (1802), a paper-making machine (1805), a machine for automatically printing bank notes with sequential serial numbers (1806), and a fountain pen (1809). He also patented the first extrusion process for making lead pipes and also machinery for making gun stocks (Patent No. 2652). His greatest contribution to engineering was his insistence on quality control. He realised that for engines to succeed, they would have to be machined to a much better standard than was the practice. He taught Arthur Woolf to machine engines to a close tolerance. This enabled Cornish engines to run with high-pressure steam, vastly increasing their output. Woolf became the leading Cornish steam engineer and his designs were adopted by all the engine designers of the day. The 15-HP engines of Watt and others of circa 1800 gave way to 450-HP engines by 1835. Bramah can be viewed as a founding father in industrial quality control.
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