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Part 9 - Pumps

Pumps move fluids (liquids or gases) such as water, natural gas or oil from wells, or for fire-fighting, sewage handling, water-cooling and hydraulic brakes and fuel supply in automobiles. They inflate tires and drive refrigerators and a wide range of industrial, chemical and medical processes. They include positive-displacement pumps such as piston pumps and rotary-types such as gear, screw, flexible vane and sliding vane pumps.

At a given speed, positive-displacement pumps produce the same flow of a (substantially incompressible) liquid regardless of discharge pressure but, if the discharge line is blocked the pressure will increase, forcing the pump to slow or stop suddenly causing the line or the pump to be severely damaged. A relief or safety valve is therefore essential. Centrifugal pumps have the advantage that they can still operate when the output is restricted by valves or blockages.

Piston pumps may be single cylinder, double acting or single acting (delivering liquid or gas on both strokes of the piston), or may have up to four cylinders. They were traditionally one of the first pumps and were used for fire fighting and boiler feed water pumps for steam engines but now are typically use to pump highly viscous fluids like concrete and heavy oils that require low flow rates against high resistance.

Joseph Michel Montgolfier, co-inventor of the hot air balloon, invented the first self-acting ram pump in 1796 to raising water for his paper mill. His friend Matthew Boulton (James Watt's partner) took out a British patent on his behalf in 1797. This hydraulic ram pump is still occasionally used in remote areas, where there is a source of low-head hydropower, and a need to pump water to a higher elevation. It takes in water at relatively low pressure and high flow-rate and uses the water hammer effect to develop pressure that lifts a portion of the input water to a point higher than where the water started. It requires no outside source of power other than the kinetic energy of flowing water.

The first centrifugal pump was described in 1475 CE by Francesco di Giorgio Martini, as one of the first pumps that would not be damaged by a blockage on the output side of the pump.

Many pumps for liquids, such as centrifugal pumps, will not pump air and must be first primed by filling it with the liquid that requires pumping. These should always be placed lower than the suction point, otherwise the pump must be filled with liquid manually. This is not a problem for positive displacement pumps, which typically have tight sealing between the moving parts and are self-priming by creating a partial vacuum that sucks water into the cylinders.

Another rotary pump, the sliding vane water pump was designed in 1588 by Agostino Ramelli and in 1593, Nicolas Grollier de Servière invented a gear pump. In 1636, a German engineer, Pappenheim, improve on the idea with a double, deep-toothed rotary gear pump powered by an overshot water wheel and used it to supply water fountains. This type of pump is still used to lubricate engines.

1650 Otto von Guericke invented the first piston vacuum pump, which used leather washers to prevent air leakage between the cylinder and the piston and leather check valves. He also demonstrated air pressure by attempting to pull apart two hollow hemispheres held together by a vacuum.

The plunger pump, patented by Sir Samuel Moreland in 1675, was similar to a piston pump but the cylinder was much larger than the plunger and the seal was on the cylinder, instead of the piston, allowing it to be used at higher pressure.

In 1687 French-born inventor Denis Papin developed the first true centrifugal pump with straight vanes for local drainage. Curved vanes were introduced by British inventor John Appold in 1851. Modern electrically powered well pumps are typically designed to operated when immersed in water and are installed at the bottom of a well hole.

In 1738 Dutch-Swiss mathematician Daniel Bernoulli described the principles of fluid dynamics. Bernoulli's equation states that if the speed of a fluid increases, the pressure will drop thereby decreasing the fluid's potential energy.

In 1790 Britain, Thomas Simpson used steam engine driven pumps for municipal water supplies. In 1845 Henry R. Worthington invented a steam powered pump to drive canal boats and U.S. naval vessels with a water jet. He later pioneered pump designs for boiler feed, oil pipeline and hydro-electric applications.

In 1849 In Seneca Falls, N.Y., Seabury S. Gould made the world's first all-metal pump.

Modern municipal systems typically supply water with a pressure of 40 psi (pounds per square inch) not only for domestic use but also to fire hydrants used for fire fighting. The pressure is maintained by continuously running pumps and by a water reservoir built on high ground or on a tower. Fire engine pumps may increase this pressure when necessary to propel water jets higher or further.