Excessive jumping of the piston rod in reciprocating compressors
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Our factory recently carried out major repairs on the secondary cylinder of the secondary reciprocating compressor, replacing the piston rod, support rings, and packing box. After reinstallation, a vibration test was conducted on the piston rod; the vertical and horizontal vibrations were around 30 microns, compared to around 8 microns before disassembly. The piston rod is connected to the crosshead via flange hydraulic bolts, which are tightened symmetrically. Someone suggested replacing the cross-head adjustment bolt, but the play was within acceptable limits before removal; it increased after the replacement, so no action was taken. I suspect that either the piston rod is deformed or there is uneven wear on the cylinder surface, and the position changed after installing a new support ring.
Anything is possible; the key issues lie in the inspections before assembly and the problems that occur during the assembly process.
The piston rod is a load-bearing component with high strength; it cannot deform without intentional striking during maintenance. I suspect it’s a problem with the newly installed support ring or piston rod, either in terms of quality or installation accuracy. You can try using an old support ring or piston rod to find out.
Please verify whether the thickness of the piston support ring has been compared with that of the original parts. Additionally, check the clearance between the crosshead slider and the guide rails
Incomplete measurements were taken before disassembly; no issues could be identified after reassembly
Check the clearance of the rod journal bearings.
First, loosen the crosshead lock nut and the packing gland fixing bolts, and measure the play of the piston rod. If this value decreases, it may be due to insufficient flatness of the lock nut surface; if it remains high, try rotating the piston rod together with the piston by about 90 degrees before measuring again to see if there is any change. If there is a change, it could be because the piston rod is bent or because the piston rod and piston are not aligned properly when assembled
It is recommended not to tighten the super nut that connects the piston to the crosshead at first; by measuring the deviation of the piston rod before and after tightening the nut, if the deviation remains the same, it is possible to adjust the thickness of the shims under or above the crosshead in order to correct this deviation. A deviation of 30 microns is not considered too large – a value of 18 microns or less meets the requirements. If there is a significant difference in the deviation of the piston rod before and after tightening the nut connecting it to the crosshead, it is very likely that the center of the thread hole in the crosshead does not align with the centerline of the piston rod.
I’m not sure if you were able to identify any issues in the end. I also wonder whether the components were checked and measured properly before installation, and whether all parameters were within the standard range after installation; it seems that the alignment is quite poor