Do reciprocating compressors not require an auxiliary oil pump?

(One of the reciprocating air compressors in our installation does not have an auxiliary oil pump; it only has an end-drive pump.) The air compressor does not operate continuously; it is started via interlock only when the pressure in the air storage tank drops to a certain low level. What types of reciprocating compressors or equipment do not require an auxiliary oil pump? ) Based on whether lubricant is used in reciprocating compressors, they can be divided into oil-lubricated and oil-free compressors. Oil-free compressors do not have oil injected into their cylinders; materials such as piston rings are self-lubricating. Generally, the large and small ends of the connecting rods still require oil lubrication, and there is oil in the crankcase. In some small oil-free compressors, there is no oil in the crankcase, they lack a crosshead structure, and their bearings are self-lubricating. Such compressors do not need an auxiliary oil pump. As LZ mentioned, in terms of lubrication, some compressors use auxiliary oil pumps, while others use shaft-end pumps. This is mainly related to the structure of the compressor, its size, and the lubrication requirements. Many air compressors with a power rating of less than 200 KW use shaft-mounted pumps, which are compact in structure and simple to operate!

Large reciprocating compressors do not have shaft-mounted pumps; instead, there are two oil pumps at the oil station, operating as one primary pump and one backup pump.

Whether a compressor requires an auxiliary oil pump is usually determined by the manufacturer during design, based on factors such as the equipment’s structure and lubrication method, to decide whether a shaft pump or an auxiliary oil pump is needed.

No way, can it work without a booster pump? How is the bearing lubricated when it first starts up?

Some small compressors are equipped with a hand pump

Ordinary piston machines are not equipped with auxiliary oil pumps. Abroad, a hand-cranked oil pump is used before starting. Based on the manufacturer’s design, structure, lubrication method, and production process.

For low-power piston engines, pump units with shaft ends are used. Due to their compact design and short oil circuits (with the length of the oil pipes generally being within 1 meter), the bearings in the crankcase are lubricated by splashing during startup. The copper sleeves on the connecting rods and crossheads are lubricated through a shaft-end pump driven by the motor, which supplies lubricating oil to various lubrication points along the oil holes in the crankshaft and connecting rods.

Reply to 8# lucy751b: Smaller compressors, such as V-type air compressors, do not have an auxiliary oil pump. During normal operation, due to their small size, low working pressure, and short oil circuits, the oil pressure is quickly generated as soon as the compressor starts up. Since these compressors are not started frequently, this approach is sufficient. Additionally, the oil in the crankcase can be forced into motion by the crankshaft, providing lubrication at first. The compressors in your factory are not started that often; therefore, the motor is likely equipped with variable frequency control, and its speed also varies. This can have adverse effects on the crankshaft and bearings. It is recommended that you install an auxiliary pump for your compressors. If you conduct an inspection, you will find that under such operating conditions, the large and small bearing shells should be damaged!

Whether there is an auxiliary oil pump is determined during the compressor’s design based on the requirements of that compressor; it is not decided based on whether it is a reciprocating or centrifugal compressor as to whether an oil pump is needed, what type of oil pump to use, or whether an auxiliary oil pump is required. Some small compressors don’t even have an oil pump!

A shaft head pump or auxiliary oil pump is used to lubricate the gaps in the transmission parts and the sealing rings; if lubrication is required inside the cylinders, a vacuum oil injection pump must be installed. Small units may not be equipped with auxiliary oil pumps (they are generally oil-free lubricated units with two rows of rolling bearings for the main bearings); since there are few parts that require lubrication, it is still necessary to turn the shaft before starting up. This action allows the shaft end pump to inject a small amount of oil into the lubrication points, thereby preventing issues such as bearing burnout.