The issue of downward displacement in reciprocating machines
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For the reciprocating machine 2D45, the downward displacement sensor is installed right above the piston rod. After the major repair in 2019, the downward displacement remained stable at around -0.20. After the major repair in 2021, the primary downward displacement fluctuated between -0.45 and -0.49 upon startup, before stabilizing at around -0.40 after a few days. The secondary downward displacement was around -0.20 upon startup, rose to around -0.35 after a few days, and then stabilized at around -0.30 during operation. What causes the different levels of settlement during the two maintenance sessions? Why was there fluctuation in the settlement level at the beginning of operation after the maintenance in 2021, and why did it stabilize later on?
First, check whether the displacement probe is loose; it is quite common for the vibrations generated by the reciprocating machine to cause the probe to become loose. The second reason is looseness at the connection between the crosshead and the piston rod; in such cases, slight abnormal noises may be heard from the middle part of the device, so it’s important to pay close attention. The third reason is wear of the guide ring on the piston (also known as a support ring).
The above common causes should all be ruled out. 1. If the probe is loose, why has it become stable now? 2. Hydraulic threaded connections are used at the joints; if they were loose, there should be abnormal noises or vibrations. 3. The newly installed components underwent a running-in period during the first few days after startup, but they shouldn’t wear out that quickly. If they did wear out so fast, why hasn’t there been any change in displacement even after several months of operation?
Have the instrumentation technician check whether the probe is loose.
If it has just been overhauled, the changes in settlement displacement may be due to installation issues or the setting of the zero point. In my opinion, it is more important to pay attention to the changes that occur after the displacement stabilizes; the fluctuations in the initial stage can be ignored
Yes, there must be a reason for the displacement changes in the early stage; if the exact cause can be identified, it will be possible to resolve these issues during the next maintenance session
Check to see if there are any issues with ground subsidence.
It is necessary to check the foundation settlement; this has happened to us before, as uneven settlement caused excessive vibration in the compressor.
1. After the maintenance is completed, are parameters such as piston rod play, clearance at the bottom of the piston, and cylinder ellipticity measured? These values should be compared with those after the major repair in 2019 to determine whether there are any issues related to installation or the equipment itself； 2. After the probe is installed, should a feeler gauge be used to check the gap between the probe and the piston rod? There may be differences in the probe’s installation position after the two maintenance sessions in 2019 and 2021. You can also check the gauge for the gap voltage value of the probe at the time of installation. 3. Personally, I think the possibility of a sinking base is very low. The fluctuations may be due to the following reasons: Firstly, the contact between the support ring and the cylinder might not be good; after some time of operation and wear, the contact improves, and thus stability is achieved. Secondly, there are differences in the installation positions of the instruments; thirdly, there may be debris at the bottom of the probe, such as lubricating oil and powder resulting from worn packing
It is likely that there are deposits on the piston rod of the instrument probe; the base is positioned relative to the ground, and the probe is installed on the compressor, so it has little to do with the base