Editing Scroll compressor (section)

==Engineering comparison to other pumps==
[[File:Scroll compressor.jpg|thumb|Scroll compressors with air tanks]]

These devices are known for operating more smoothly, quietly, and reliably than conventional compressors in some applications.<ref>{{cite web |url=http://www.poweredbythepeople.com/categories/hvac.php |title=HVAC Compressor |publisher=Powered by the People Resources Company |date=July 2010 |access-date=July 21, 2010 |archive-date=October 20, 2014 |archive-url=https://web.archive.org/web/20141020211254/http://www.poweredbythepeople.com/categories/hvac.php |url-status=live }}</ref>

===Rotations and pulse flow===
[[File:Scroll Compressor.jpeg|thumb|Open-type scroll compressor]]

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 compressors 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.

===Valves===
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).<ref>{{cite journal |author=Jim Wheeler |date=November 1988 |title=Scroll Compressors: The Inside Story |journal=Contracting Business |pages=36 |publisher=Penton Media }}</ref><ref>{{cite journal |first1=James W. |last1=Bush |first2=John P. |last2=Elson |title=Scroll Compressor Design Criteria for Residential Air Conditioning and Heat Pump Applications |journal=Proceedings of the 1988 International Compressor Engineering Conference |volume=1 |pages=83–92 |date=July 1988 }}</ref>

===Efficiency===
The [[isentropic]] efficiency of scroll compressors is slightly higher than that of a typical reciprocating compressor when the compressor is designed to operate near one selected rating point.<ref>{{cite conference|last1=Elson|first1=John P.|last2=Kaemmer|first2=Norbert|last3=Wang|first3=Simon|last4=Perevozchikov|first4=Michael|title=Scroll Technology: An Overview of Past, Present, and Future Developments|conference=International Compressor Engineering Conference|date=July 14–17, 2008|url=https://docs.lib.purdue.edu/icec/1871|access-date=May 9, 2019|archive-date=May 9, 2019|archive-url=https://web.archive.org/web/20190509180632/https://docs.lib.purdue.edu/icec/1871/|url-status=live}}</ref> The scroll compressors are more efficient in this case because they do not have a dynamic discharge valve that introduces additional throttling losses. However, the efficiency of a scroll compressor that does not have a discharge valve begins to decrease as compared to the reciprocating compressor at higher pressure ratio operation. This is a result of under-compression losses that occur at high pressure ratio operation of the positive displacement compressors that do not have a dynamic discharge valve.

The scroll compression process is nearly 100% [[volumetric]]ally efficient in pumping the trapped fluid. The suction process creates its own volume, separate from the compression and discharge processes further inside. By comparison, reciprocating compressors leave a small amount of compressed gas in the cylinder, because it is not practical for the piston to touch the head or valve plate. That remnant gas from the last cycle then occupies space intended for suction gas. The reduction in capacity (i.e. volumetric efficiency) depends on the suction and discharge pressures with greater reductions occurring at higher ratios of discharge to suction pressures.

===Size===
Scroll compressors tend to be very compact and smooth running and so do not require spring suspension. This allows them to have very small shell enclosures which reduces overall cost but also results in smaller free volume.<ref>{{cite web |title=Scanning for Ideas: Air Squared Developed World's Smallest Continuous-Duty Scroll Compressor |url=https://www.machinedesign.com/news/scanning-ideas-air-squared-developed-world-s-smallest-continuous-duty-scroll-compressor |website=[[Machine Design]] |publisher=[[Penton Media]] |access-date=November 16, 2021 |date=May 19, 2011 |archive-date=May 9, 2019 |archive-url=https://web.archive.org/web/20190509165012/https://www.machinedesign.com/news/scanning-ideas-air-squared-developed-world-s-smallest-continuous-duty-scroll-compressor |url-status=live }}</ref>