The reverse angle problem of reciprocating compressors
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The reverse angle issue in reciprocating compressors: A imported compressor with three-stage compression experienced frequent damage to the small bushings of the crossheads in the third stage during operation. Tests conducted by specialized firms revealed that this problem was caused by a reverse angle of zero under certain operating conditions. What improvements can be made, and what are the relevant regulations?
Check for any scratches on the connecting rod and the crosshead, as well as whether there are any issues with the crosshead pins moving up and down during operation； As the crankshaft rotates one full circle, check whether the centerlines of the large and small connecting rod bearings are aligned, and whether there are any issues with the crosshead pins in the left or right direction.
The poster’s question has been identified as being caused by a zero reverse angle, which led to the burnout of the small-end bearing shells. API618 specifies that for slotless stub bushings, the reverse angle must be at least 45°, and the reverse peak must be at least 20% ； For slotted small-end bushings, the reverse angle must be at least 15°, and the reverse peak must be at least 3%. Because during the startup phase, the inlet pressure, back pressure, etc., are different from the design conditions, resulting in a reverse angle of zero. The parameters for the startup operating condition can be recalculated for the reverse angle; if they do not meet the requirements, the operating conditions should be adjusted before attempting to start up again.
This is a design-related issue; it is recommended to ask the manufacturer to make adjustments as soon as possible.
To address this issue, it was resolved by adding a third-stage tail rod; however, leaks in the tail rod gasket are difficult to handle
This post was last edited by zhangya*ong on 2015-8-19 at 15:43. The issue of piston force balance has been taken into account in the compressor design. Through the proper arrangement of cylinders (such as a symmetrically balanced compressor), the piston forces can essentially be kept in balance. If balance cannot be achieved, additional tail rods or balance sections must be used to achieve it; otherwise, the compressor will experience vibration during operation. The balance section only serves to counteract the force of the piston; it does not consume any work.
Prevents failure of the shaft-side intake valve, prevents failure of the cover-side exhaust valve, adds a third-stage tail rod, and minimizes the impact of the variable air volume control system.
Special operating conditions need to be mentioned at the time of purchase; the manufacturer will conduct an assessment. If they are not mentioned, subsequent modifications will be rather troublesome
For such issues, it’s sufficient to report them to the manufacturer in a timely manner and adjust the manufacturing process accordingly