On the issue of severe increase in crosshead vibration after load switching in reciprocating compressors
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The 2D45 Faraday reciprocator machine features two-stage compression, with a normal load of 100%. When the machine is shut down and the load drops to 50%, vibration in the crosshead of the second-stage cylinder as well as in the crankcase increases suddenly, accompanied by a banging sound. After shutdown, it was checked that the big end bearings of the connecting rods were in good condition, and there was no signs of looseness in the crosshead or piston bodies; the cause of this issue is unknown.
Reduce the load to 50 percent; the imbalance in forces on the piston rod is the cause
Align the motor and check the foot bolts.
Check whether the fuselage is level and the cylinders are also level? Is there wavy wear on the cylinder liner?
It may be related to unit alignment and uneven pressure on the piston surface
After the load is adjusted to 50%, it is caused by the changes in force acting on the piston
I don’t think this has much to do with a decrease in flow rate; it’s likely that changes in pressure or rotational speed cause variations in piston force. Under certain conditions, the imbalance in piston force increases, leading to heightened vibration
In the past, when shutting down, it was normal for it to drop from 100 to 50
It is also possible that, after the piston assembly and crosshead assembly reach force equilibrium at 50% load, they collide back and forth with the crosshead pin under the action of oil pressure