Hydraulic motor: what is it ?
The hydraulic engine is a hydraulic power machine which transforms the energy of a liquid into the energy of a solid body using in order to do so pistons, gear wheels or vane rotors.
The hydraulic motors can be generally speaking linear or rotary engines. The linear ones are also called hydraulic cylinders and use the pressure of a liquid to produce the linear movement of a solid body, the rotary engines instead use the pressure of a liquid to produce a rotary movement of a solid body.
Hydraulic engines also called hydro motors, are reversible machines, meaning that once a mechanical energy is applied on them, they transfer it to the liquid augmenting liquid pressure. If the liquid in discussion is water then the effect is raising it’s hydraulic power exponentially.
How does it work ?
Most of hydraulic pumps are reversible machines, this means that they can also work as hydraulic motors. Similarly to the case of electric engines, to which the speed modification is made by modifying rotary’s power, for hydraulic motors speed is correlated to the liquid flow rate which operates the engine, speed being adjustable by modifying it or by regulating the volume of suction and relief.
William Armstrong : a little history never killed nobody
One of the first rotary hydraulic motors to be developed was that constructed by William Armstrong for his Swing Bridge over the River Tyne. Two motors were provided, for reliability. Each one was a three-cylinder single-acting oscillating engine. Armstrong developed a wide range of hydraulic motors, linear and rotary, that were used for a wide range of industrial and civil engineering tasks, particularly for docks and moving bridges.
William George Armstrong, 1st Baron Armstrong (26 November 1810 – 27 December 1900) was an English engineer and industrialist. He was also an eminent scientist, inventor and philanthropist. In collaboration with the architect Richard Norman Shaw, he built Cragside in Northumberland, the first house in the world to be lit by hydroelectricity. He is regarded as the inventor of modern artillery. Armstrong was knighted in 1859 after giving his gun patents to the government. In 1887, in Queen Victoria’s golden jubilee year, he was raised to the peerage as Baron Armstrong of Cragside.
Armstrong was a very keen angler, and while fishing on the River Dee at Dentdale in the Pennines, he saw a waterwheel in action, supplying power to a marble quarry. It struck Armstrong that much of the available power was being wasted. When he returned to Newcastle, he designed a rotary engine powered by water, and this was built in the High Bridge works of his friend Henry Watson.
Unfortunately, little interest was shown in the engine. Armstrong subsequently developed a piston engine instead of a rotary one and decided that it might be suitable for driving a hydraulic crane. In 1846 his work as an amateur scientist was recognized when he was elected a Fellow of the Royal Society.
The evolution of the hydraulic motor
The first simple fixed-stroke hydraulic motors had the disadvantage that they used the same volume of water whatever the load and so were wasteful at part-power. Unlike steam engines, as water is incompressible, they could not be throttled or their valve cut-off controlled. To overcome this, motors with variable stroke were developed.
Adjusting the stroke, rather than controlling admission valves, now controlled the engine power and water consumption. One of the first of these was Arthur Rigg’s patent engine of 1886. This used a double eccentric mechanism, as used on variable stroke power presses, to control the stroke length of a three cylinder radial engine. Later, the swashplate engine with an adjustable swashplate angle would become a popular way to make variable stroke hydraulic motors.
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