[Mechanical Equipment Technology Edition] Daily Question 20171120: Lubrication System of Screw Compressor Units (9)
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This post was last edited by YORK Industrial Refrigeration on 2017-11-23 at 08:20. Starting from now, in order to enhance communication among users, a \"Question of the Day\" activity has been launched on the Mechanical Equipment Technology forum. We hope everyone will participate actively to progress and improve together! ! ! Rewards: 3 points for active participation, 10-15 points for correct answers. This question is valid for two days; no scoring will be given after that period. Last time we discussed the methods of supplying oil to screw compressors. Why do some screw compressors require oil to be supplied only by an oil pump, while others can use either an oil pump or a pressure difference mechanism? What factors on the compressor determine the method of oil supply? Answer: It mainly depends on the type of bearing; for example, Yantai Binglun has always used oil pumps to supply oil. Why is that? He uses shaft bearings (sliding bearings), whereas the sliding bearings used in compressors that are fed with oil by an auxiliary oil pump or directly through pressure differences are roller bearings; there is no such thing as a shaft bearing type in those cases. ================================ High-quality promotions: Mechanical equipment——Maintenance procedures for York screw compressors https://bbs.hcbbs.com/thread-1806833-1-1.html Mechanical equipment——Upgrading of York Quinton control centers https://bbs.hcbbs.com/thread-1804837-1-1.html Mechanical equipment——Major repairs for GEA Grasox screw compressors https://bbs.hcbbs.com/thread-1800467-1-1.html Mechanical equipment——Disassembly and maintenance of British HOWDEN screw compressors https://bbs.hcbbs.com/thread-1832529-1-1.html Mechanical equipment——Disassembly and maintenance of Japanese Maekawa MYCOM screw compressors https://bbs.hcbbs.com/forum.php?mod=viewthread&tid=1786445
Equipment equipped with oil pumps generally operates at high speeds, has a wide range of load adjustments, and requires timely lubrication of its components. It is a relatively high-end device. There are two scenarios involving an oil pump: one is pre-lubrication at startup. Stopping the oil pump after the system starts up or once the oil pressure is established has the advantage of lubricating the compressor bearings and worn components before operation, thereby creating an oil film that reduces the likelihood of failures. Second scenario: The compressor has to operate under various operating conditions, and the system cannot ensure the establishment of an oil pressure oil film; therefore, forced lubrication is required. In cases such as high-temperature components, operation under low-temperature conditions or in special operating environments, the parts inside the compressor require continuous lubrication by an oil film; therefore, an oil pump must operate continuously to ensure the proper functioning of the machine. It depends on factors such as the material components of the equipment, the system design, and the operating conditions. Oil-free pumps generally require stable operating conditions, have a limited range of load adjustment, and are considered standard equipment.
Semi-hermetic compressors generally have a small capacity, with relatively light bearing loads; they usually use rolling bearings and do not require much lubricating oil. Oil return can be achieved through the pressure difference once it is established, which is usually sufficient to meet the lubrication needs during operation. But most of the time, a small pre-lubrication oil pump is still required when starting up. Open-type units generally have a large capacity, resulting in high bearing loads; sliding bearings are mostly used in such units. Pre-lubrication is required before starting up to protect the bearings, and a significant amount of lubricating oil is needed. Relying solely on pressure differences to supply oil may not be sufficient to meet the lubrication requirements, so an oil pump is necessary to provide the oil.
Oil-screw compressors use a forced-circulation oil injection lubrication method, in which cooled lubricating oil is directly injected into the compressor chamber during the compression process. The amount of oil injected is much greater than that used for lubrication in piston compressors, as well as in other rotary compressors that do not utilize oil injection. All the lubricating oil injected into the chamber mixes with the compressed gas and is then discharged from the chamber; it passes through an oil-gas separator to enable maximum recovery and recycling of the lubricating oil. Large multi-stage oil-injected compressors are equipped with a separate oil supply system (using an oil pump), while small single-stage oil-injected compressors rely on the pressure difference of gases to achieve oil injection for lubrication!
The oil supply for compressors depends mainly on factors such as the material components of the equipment, different types of system configurations, and the design operating conditions.
In open-type screw compressors, the capacity is large and the load on the bearings is high; therefore, sliding bearings are more commonly used, which requires forced lubrication, that is, oil supply through an oil pump. In semi-closed screw compressors, rolling bearings are generally used, and the amount of lubricating oil required is not large, so differential pressure lubrication can be employed; oil pump supply can also be used if conditions permit.