Scroll compressor

A scroll compressor (also called spiral compressor, scroll pump and scroll vacuum pump) is a device for compressing air or refrigerant. It is used in air conditioning equipment, as an automobile supercharger (where it is known as a scroll-type supercharger) and as a vacuum pump. Many residential central heat pump and air conditioning systems and a few automotive air conditioning systems employ a scroll compressor instead of the more traditional rotary, reciprocating, and wobble-plate compressors. A scroll compressor (also called spiral compressor, scroll pump and scroll vacuum pump) is a device for compressing air or refrigerant. It is used in air conditioning equipment, as an automobile supercharger (where it is known as a scroll-type supercharger) and as a vacuum pump. Many residential central heat pump and air conditioning systems and a few automotive air conditioning systems employ a scroll compressor instead of the more traditional rotary, reciprocating, and wobble-plate compressors. A scroll compressor operating in reverse is known as a scroll expander, and can be used to generate mechanical work from the expansion of a fluid, compressed air or gas. Léon Creux first patented a scroll compressor in 1905 in France and the US (Patent number 801182).Creux invented the compressor as a rotary steam engine concept, but the metal casting technology of the period was not sufficiently advanced to construct a working prototype, since a scroll compressor demands very tight tolerances to function effectively. In the 1905 patent, Creux defines a co-orbiting or spinning reversible steam expander driven by a fixed radius crank on a single shaft. However, the scroll expander engine could not overcome the machining hurdles of radial compliance inherit to achieving efficiency in scroll operation that would not be adequately addressed until the works of Niels Young in 1975. The first practical scroll compressors did not appear on the market until after World War II, when higher-precision machine tools enabled their construction. In 1981, Sanden began manufacturing the first commercially available scroll compressors for automobile air conditioners. They were not commercially produced for air conditioning until 1983 when Hitachi launched the world's first air conditioner with a scroll compressor. A scroll compressor uses two interleaving scrolls to pump, compress or pressurize fluids such as liquids and gases. The vane geometry may be involute, Archimedean spiral, or hybrid curves. Often, one of the scrolls is fixed, while the other orbits eccentrically without rotating, thereby trapping and pumping or compressing pockets of fluid between the scrolls. Another method for producing the compression motion is co-rotating the scrolls, in synchronous motion, but with offset centers of rotation. The relative motion is the same as if one were orbiting. Another variation is with flexible (layflat) tubing where the archimedean spiral acts as a peristaltic pump, which operates on much the same principle as a toothpaste tube. They have casings filled with lubricant to prevent abrasion of the exterior of the pump tube and to aid in the dissipation of heat, and use reinforced tubes, often called 'hoses'. This class of pump is often called a 'hose pumper'. Since there are no moving parts in contact with the fluid, peristaltic pumps are inexpensive to manufacture. Their lack of valves, seals and glands makes them comparatively inexpensive to maintain, and the hose or tube is a low-cost maintenance item compared to other pump types. These devices are known for operating more smoothly, quietly, and reliably than conventional compressors in some applications. Unlike pistons, the orbiting scroll’s mass can be perfectly counterbalanced, with simple masses, to minimize vibration. (An orbiting scroll cannot be balanced if Oldham coupling is used.) The scroll’s gas processes are more continuous. Additionally, a lack of dead space gives an increased volumetric efficiency. The compression process occurs over approximately 2 to 2½ rotations of the crankshaft, compared to one rotation for rotary compressors, and one-half rotation for reciprocating compressors. The scroll discharge and suction processes occur for a full rotation, compared to less than a half-rotation for the reciprocating suction process, and less than a quarter-rotation for the reciprocating discharge process. Reciprocating compressor have multiple cylinders (typically, anywhere from two to six), while scroll compressors only have one compression element. The presence of multiple cylinders in reciprocating compressors reduces suction and discharge pulsations. Therefore, it is difficult to state whether scroll compressors have lower pulsation levels than reciprocating compressors as has often been claimed by some suppliers of scroll compressors. The more steady flow yields lower gas pulsations, lower sound and lower vibration of attached piping, while having no influence on the compressor operating efficiency. Scroll compressors never have a suction valve, but depending on the application may or may not have a discharge valve. The use of a dynamic discharge valve is more prominent in high pressure ratio applications, typical of refrigeration. Typically, an air-conditioning scroll does not have a dynamic discharge valve. The use of a dynamic discharge valve improves scroll compressor efficiency over a wide range of operating conditions, when the operating pressure ratio is well above the built-in pressure ratio of the compressors. If the compressor is designed to operate near a single operating point, then the scroll compressor can actually gain efficiency around this point if there is no dynamic discharge valve present (since there are additional discharge flow losses associated with the presence of the discharge valve as well as discharge ports tend to be smaller when the discharge is present).